En Route Operations
3-1The en route phase of flight has seen some of the most
dramatic improvements in the way pilots navigate
from departure to destination. Developments in technology have played a significant role in most of these
improvements. Computerized avionics and advanced
navigation systems are commonplace in both general
and commercial aviation.
The procedures employed in the en route phase of flight
are governed by a set of specific flight standards established by Title 14 of the Code of Federal Regulations
(14 CFR), Federal Aviation Administration (FAA)
Order 8260.3, United States Standard for Terminal
Instrument Procedures (TERPS), and related publications. These standards establish courses to be flown,
obstacle clearance criteria, minimum altitudes, navigation performance, and communications requirements.
For the purposes of this discussion, the en route phase of
flight is defined as that segment of flight from the termination point of a departure procedure to the origination
point of an arrival procedure.
EN ROUTE NAVIGATION
Part 91.181 is the basis for the course to be flown. To
operate an aircraft within controlled airspace under
instrument flight rules (IFR), pilots must either fly
along the centerline when on a Federal airway or, on
routes other than Federal airways, along the direct
course between navigational aids or fixes defining the
route. The regulation allows maneuvering to pass well
clear of other air traffic or, if in visual flight rules
(VFR) conditions, to clear the flight path both before
and during climb or descent.
En route IFR navigation is evolving from the ground
based navigational aid (NAVAID) airway system to a
sophisticated satellite and computer-based system that
can generate courses to suit the operational requirements of almost any flight. Although the promise of
the new navigation systems is immense, the present
system of navigation serves a valuable function and is
expected to remain for a number of years.
The procedures pilots employ in the en route phase of
flight take place in the structure of the National
Airspace System (NAS) consisting of three strata. The
first, or lower stratum is an airway structure that
extends from the base of controlled airspace up to but
not including 18,000 feet mean sea level (MSL). The
second stratum is an area containing identifiable jet
routes as opposed to designated airways, and extends
from 18,000 feet MSL to Flight Level (FL) 450. The
third stratum, above FL 450 is intended for random,
point-to-point navigation.
AIR ROUTE TRAFFIC CONTROL CENTERS
The Air Route Traffic Control Center (ARTCC)
encompasses the en route air traffic control system
air/ground radio communications, that provides safe
and expeditious movement of aircraft operating on IFR
within the controlled airspace of the Center. ARTCCs
provide the central authority for issuing IFR clearances
and nationwide monitoring of each IFR flight. This
applies primarily to the en route phase of flight, and
includes weather information and other inflight services. There are 20 ARTCCs in the conterminous United
States (U.S.), and each Center contains between 20 to
80 sectors, with their size, shape, and altitudes determined by traffic flow, airway structure, and workload.
Appropriate radar and communication sites are connected to the Centers by microwave links and telephone
lines.
The CFRs require the pilot in command under IFR in
controlled airspace to continuously monitor an appropriate Center or control frequency. When climbing after
takeoff, an IFR flight is either in contact with a radarequipped local departure control or, in some areas, an
ARTCC facility. As a flight transitions to the en route
phase, pilots typically expect a handoff from departure
control to a Center frequency if not already in contact
with the Center. The FAA National Aeronautical
Charting Office (NACO) publishes en route charts
depicting Centers and sector frequencies, as shown in
Figure 3-2 on page 3-2. During handoff from one Center
to another, the previous controller assigns a new frequency. In cases where flights may be still out of range,
the Center frequencies on the face of the chart are very
helpful. In Figure 3-2 on page 3-2, notice the boundary
between Memphis and Atlanta Centers, and the
remoted sites with discrete very high frequency (VHF)
and ultra high frequency (UHF) for communicating
with the appropriate ARTCC. These Center frequency
boxes can be used for finding the nearest frequency
within the aircraft range. They also can be used
3-2
for making initial contact with the Center for clearances.
The exact location for the Center transmitter is not
shown, although the frequency box is placed as close as
possible to the known location.
During the en route phase, as a flight transitions from
one Center facility to the next, a handoff or transfer of
control is required as previously described. The handoff procedure is similar to the handoff between other
Cleveland
Center
Albuquerque
Center
Seattle
Center
Atlanta Center
Chicago
Center
Boston Center
Washington Center (DC)
Denver Center
Fort Worth Center
Houston Center
Indianapolis
Center
Jacksonville Center
Kansas City Center
Los Angeles Center
Salt Lake City
Center
Miami Center
Memphis
Center
Minneapolis Center
New York
Center
ZID
ZMP
ZOB
ZBW
ZNY
ZNY
ZDC
ZAU
ZKC
ZME
ZTL
ZJX
ZMA
ZHU
ZFW
ZAB
ZDV
ZLA
ZOA
ZLC
ZSE
Oakland Center
Honolulu
Center
ZHN
Anchorage
Center
ZAN
Figure 3-1. Air Route Traffic Control Centers.
Figure 3-2. ARTCC Centers and Sector Frequencies.
3-3
radar facilities, such as departure or approach control.
During the handoff, the controller whose airspace is
being vacated issues instructions that include the name
of the facility to contact, appropriate frequency, and
other pertinent remarks.
Accepting radar vectors from controllers does not relieve
pilots of their responsibility for safety of flight. Pilots
must maintain a safe altitude and keep track of their position, and it is their obligation to question controllers,
request an amended clearance, or, in an emergency, deviate from their instructions if they believe that the safety
of flight is in doubt. Keeping track of altitude and position when climbing, and during all other phases of flight,
are basic elements of situational awareness. Aircraft
equipped with an enhanced ground proximity warning
system (EGPWS) or terrain awareness and warning system (TAWS) and traffic alert and collision avoidance
system (TCAS) help pilots detect and correct unsafe altitudes and traffic conflicts. Regardless of equipment,
pilots must always maintain situational awareness
regarding their location and the location of traffic in their
vicinity.
PREFERRED IFR ROUTES
A system of preferred IFR routes helps pilots, flight
crews, and dispatchers plan a route of flight to minimize route changes, and to aid in the efficient, orderly
management of air traffic using Federal airways.
Preferred IFR routes are designed to serve the needs of
airspace users and to provide for a systematic flow of
air traffic in the major terminal and en route flight environments. Cooperation by all pilots in filing preferred
routes results in fewer air traffic delays and better efficiency for departure, en route, and arrival air traffic
service.
Preferred IFR routes are published in the
Airport/Facility Directory for the low and high altitude
stratum. If they begin or end with an airway number, it
indicates that the airway essentially overlies the airport
and flights normally are cleared directly on the airway.
Preferred IFR routes beginning or ending with a fix
indicate that pilots may be routed to or from these fixes
via a standard instrument departure (SID) route, radar
vectors, or a standard terminal arrival route (STAR).
Routes for major terminals are listed alphabetically
under the name of the departure airport. Where several
airports are in proximity they are listed under the principal airport and categorized as a metropolitan area;
e.g., New York Metro Area. One way preferred IFR
routes are listed numerically showing the segment fixes
and the direction and times effective. Where more than
one route is listed, the routes have equal priority for
use. Official location identifiers are used in the route
description for very high frequency omnidirectional
ranges (VORs) and very high frequency omnidirectional ranges/tactical air navigation (VORTACs), and
intersection names are spelled out. The route is direct
where two NAVAIDs, an intersection and a NAVAID, a
NAVAID and a NAVAID radial and distance point, or
any navigable combination of these route descriptions
follow in succession.
SUBSTITUTE EN ROUTE FLIGHT PROCEDURES
Air route traffic control centers are responsible for specifying essential substitute airway and route segments and
fixes for use during VOR/VORTAC shutdowns.
Scheduled shutdowns of navigational facilities require
planning and coordination to ensure an uninterrupted
flow of air traffic. A schedule of proposed facility shutdowns within the region is maintained and forwarded as
far in advance as possible to enable the substitute routes
to be published. Substitute routes are normally based on
VOR/VORTAC facilities established and published for use in
the appropriate altitude strata. In
the case of substitute routes in
the upper airspace stratum, it may
be necessary to establish routes
by reference to VOR/VORTAC
facilities used in the low altitude
system. Nondirectional radio beacon (NDB) facilities may only be
used where VOR/VORTAC coverage is inadequate and ATC
requirements necessitate use
of such NAVAIDs. Where
operational necessity dictates,
navigational aids may be used
beyond their standard service
volume (SSV) limits, provided that the routes can be
given adequate frequency protection.
Figure 3-3. Preferred IFR Routes.
3-4
The centerline of substitute routes must be contained
within controlled airspace, although substitute routes
for off-airway routes may not be in controlled airspace. Substitute routes are flight inspected to verify
clearance of controlling obstacles and to check for
satisfactory facility performance. To provide pilots
with necessary lead time, the substitute routes are submitted in advance of the en route chart effective date. If
the lead time cannot be provided, the shutdown may be
delayed or a special graphic NOTAM may be considered. Normally, shutdown of facilities scheduled for 28
days (half the life of the en route chart) or less will not
be charted. The format for describing substitute routes
is from navigational fix to navigational fix. A minimum
en route altitude (MEA) and a maximum authorized
altitude (MAA) is provided for each route segment.
Temporary reporting points may be substituted for the
out-of-service facility and only those other reporting
points that are essential for air traffic control. Normally,
temporary reporting points over intersections are not
necessary where Center radar coverage exists. A minimum reception altitude (MRA) is established for each
temporary reporting point.
TOWER EN ROUTE CONTROL
Within the NAS it is possible to fly an IFR flight without leaving approach control airspace, using tower en
route control (TEC) service. This helps expedite air
traffic and reduces air traffic control and pilot communication requirements. TEC is referred to as “tower en
route,” or “tower-to-tower,” and allows flight beneath
the en route structure. Tower en route control reallocates airspace both vertically and geographically to
allow flight planning between city pairs while remaining with approach control airspace. All users are
encouraged to use the TEC route descriptions in the
Airport/Facility Directory when filing flight plans. All
published TEC routes are designed to avoid en route
airspace, and the majority are within radar coverage.
The graphic depiction of TEC routes is not to be used
for navigation or for detailed flight planning. Not all
city pairs are depicted. It is intended to show geographic areas connected by tower en route control.
Pilots should refer to route descriptions for specific
flight planning. The word “DIRECT” appears as the
route when radar vectors are used or no airway exists.
Also, this indicates that a SID or STAR may be
assigned by ATC. When a NAVAID or intersection
identifier appears with no airway immediately preceding or following the identifier, the routing is understood
to be direct to or from that point unless otherwise
cleared by ATC. Routes beginning and ending with an
airway indicate that the airway essentially overflies
the airport, or radar vectors will be issued. Where
more than one route is listed to the same destination,
ensure that the correct route for the type of aircraft
classification has been filed. These are denoted after
the route in the altitude column using J (jet powered),
M (turbo props/special, cruise speed 190 knots or
greater), P (non-jet, cruise speed 190 knots or
greater), or Q (non-jet, cruise speed 189 knots or less).
Although all airports are not listed under the destination column, IFR flights may be planned to satellite
airports in the proximity of major airports via the
same routing. When filing flight plans, the coded
route identifier, i.e., BURL1, VTUL4, or POML3,
may be used in lieu of the route of flight.
AIRWAY AND ROUTE SYSTEM
The present en route system is based on the VHF airway/route navigation system. Low frequency (LF) and
integrated LF/VHF airways and routes have gradually
been phased out in the conterminous U.S., with some
remaining in Alaska.
MONITORING OF NAVIGATION FACILITIES
VOR, VORTAC, and instrument landing system (ILS)
facilities, as well as most nondirectional radio beacons (NDBs) and marker beacons installed by the
FAA, are provided with an internal monitoring feature. Internal monitoring is provided at the facility
through the use of equipment that causes a facility
shutdown if performance deteriorates below established tolerances. A remote status indicator also may
be provided through the use of a signal-sampling
receiver, microwave link, or telephone circuit. Older
FAA NDBs and some non-Federal NDBs do not have
the internal feature and monitoring is accomplished
by manually checking the operation at least once each
hour. FAA facilities such as automated flight service
stations (AFSSs) and ARTCCs/sectors are usually the
control point for NAVAID facility status. Pilots can
query the appropriate FAA facility if they have questions in flight regarding NAVAID status, in addition to
checking notices to airmen (NOTAMs) prior to flight,
since NAVAIDs and associated monitoring equipment
are continuously changing.
LF AIRWAYS/ROUTES
Numerous low frequency airways still exist in Alaska,
as depicted in this NACO en route low altitude chart
excerpt near Nome, Alaska. Colored LF
east and west airways G7, G212 (green), and R35 (red),
are shown, along with north and south airways B2, B27
(blue), and A1 (amber), all based upon the Fort Davis
NDB en route NAVAID. The nearby Nome VORTAC
VHF en route NAVAID is used with victor airways
V452, V333, V507, V506, and V440.
3-5
Figure 3-4. Tower En Route Control.
Figure 3-5. LF and VHF Airways — Alaska.
3-6
VHF AIRWAYS/ROUTES
Figure 3-6 depicts numerous arrowed, single direction
jet routes on this excerpt from a NACO en route high
altitude chart, effective at and above 18,000 feet MSL
up to and including FL 450. Notice the MAAs of 41,000
and 29,000 associated with J24 and J193, respectively.
Additionally, note the BAATT, NAGGI, FUMES, and
MEYRA area navigation (RNAV) waypoints.
Waypoints are discussed in detail later in this chapter.
VHF EN ROUTE OBSTACLE CLEARANCE AREAS
All published routes in the NAS are based on specific
obstacle clearance criteria. An understanding of en
route obstacle clearance areas helps with situational
awareness and may help avoid controlled flight into terrain (CFIT). Obstacle clearance areas for the en route
phase of flight are identified as primary, secondary, and
turning areas.
The primary and secondary area obstacle clearance criteria, airway and route widths, and the ATC separation
procedures for en route segments are a function of
safety and practicality in flight procedures. These flight
procedures are dependent upon the pilot, the aircraft,
and the navigation system being used, resulting in a
total VOR system accuracy factor, along with an associated probability factor. The pilot/aircraft information
component of these criteria includes pilot ability to
track the radial and the flight track resulting from turns
at various speeds and altitudes under different wind
conditions. The navigation system information
includes navigation facility radial alignment displacement, transmitter monitor tolerance, and receiver
accuracy. All of these factors were considered during
development of en route criteria. From this analysis,
the computations resulted in a total system accuracy
of ±4.5° 95 percent of the time and ±6.7° 99 percent
of the time. The 4.5° figure became the basis for primary area obstacle clearance criteria, airway and
route widths, and the ATC separation procedures. The
6.7° value provides secondary obstacle clearance area
dimensions. Figure 3-7 depicts the primary and secondary obstacle clearance areas.
PRIMARY AREA
The primary obstacle clearance area has a protected
width of 8 nautical miles (NM) with 4 NM on each
side of the centerline. The primary area has widths of
route protection based upon system accuracy of a
±4.5° angle from the NAVAID. These 4.5° lines
extend out from the NAVAID and intersect the boundaries of the primary area at a point approximately 51
NM from the NAVAID. Ideally, the 51 NM point is
where pilots would change over from navigating away
from the facility, to navigating toward the next facility, although this ideal is rarely achieved.
If the distance from the NAVAID to the changeover
point (COP) is more than 51 NM, the outer boundary
of the primary area extends beyond the 4 NM width
along the 4.5° line when the COP is at midpoint. This
Figure 3-6. VHF Jet Routes.
3-7
means the primary area, along with its obstacle clearance criteria, is extended out into what would have
been the secondary area. Additional differences in the
obstacle clearance area result in the case of the effect of
an offset COP or dogleg segment. For protected en
route areas the minimum obstacle clearance in the primary area, not designated as mountainous under Part
95 — IFR altitude is 1,000 feet over the highest obstacle.
Mountainous areas for the Eastern and Western U.S.
are designated in Part 95, as shown in Figure 3-9 on
page 3-8. Additional mountainous areas are designated for Alaska, Hawaii, and Puerto Rico. With some
exceptions, the protected en route area minimum
obstacle clearance over terrain and manmade obstacles in mountainous areas is 2,000 feet. Obstacle
clearance is sometimes reduced to not less than 1,500
feet above terrain in the designated mountainous areas
of the Eastern U.S., Puerto Rico, and Hawaii, and may
be reduced to not less than 1,700 feet in mountainous
areas of the Western U.S. and Alaska. Consideration is
given to the following points before any altitudes providing less than 2,000 feet of terrain clearance are
authorized:
• Areas characterized by precipitous terrain.
• Weather phenomena peculiar to the area.
• Phenomena conducive to marked pressure differentials.
• Type of and distance between navigational facilities.
• Availability of weather services throughout the
area.
• Availability and reliability of altimeter resetting
points along airways and routes in the area.
Altitudes providing at least 1,000 feet of obstacle clearance over towers and/or other manmade obstacles may
be authorized within designated mountainous areas if
the obstacles are not located on precipitous terrain where
Bernoulli Effect is known or suspected to exist.
4.5°
4.5°
51
51
4.5°
4.5°
4 NM
4 NM
4 NM
4 NM
2 NM
2 NM
6.7°
6.7°
6.7°
6.7°
51
51
Primary Obstacle Clearance Area
Secondary Obstacle Clearance Area
Figure 3-7. VHF En Route Obstacle Clearance Areas.
1,000 Feet Above
Highest Obstacle
Primary En Route
Obstacle Clearance Area
Nonmountainous Area
Figure 3-8. Obstacle Clearance - Primary Area.
3-8
Bernoulli Effect, atmospheric eddies, vortices, waves,
and other phenomena that occur in conjunction with disturbed airflow associated with the passage of strong
winds over mountains can result in pressure deficiencies
manifested as very steep horizontal pressure gradients.
Since downdrafts and turbulence are prevalent under
these conditions, potential hazards may be multiplied.
SECONDARY AREA
The secondary obstacle clearance area extends along a
line 2 NM on each side of the primary area. Navigation
system accuracy in the secondary area has widths of
route protection of a ±6.7° angle from the NAVAID.
These 6.7° lines intersect the outer boundaries of the secondary areas at the same point as primary lines, 51 NM
from the NAVAID. If the distance from the NAVAID to
the COP is more than 51 NM, the secondary area
extends along the 6.7° line when the COP is at midpoint. In all areas, mountainous and nonmountainous,
obstacles that are located in secondary areas are considered as obstacles to air navigation if they extend
above the secondary obstacle clearance plane. This
plane begins at a point 500 feet above the obstacles
upon which the primary obstacle clearance area is
based, and slants upward at an angle that causes it to
intersect the outer edge of the secondary area at a point
500 feet higher.
The obstacle clearance areas for LF airways and routes
are different than VHF, with the primary and secondary
area route widths both being 4.34 NM. The accuracy
lines are 5.0° in the primary obstacle clearance area and
7.5° in the secondary area. Obstacle clearance in the
primary area of LF airways and routes is the same as
that required for VHF, although the secondary area
obstacle clearance requirements are based upon distance from the facility and location of the obstacle
relative to the inside boundary of the secondary area.
Figure 3-9. Designated Mountainous Areas.
Puerto Rico
Mountainous Area
67° 66°30' 66°
20°
25°
67° 66°30' 66°
30°
35°
40°
45°
75°
85°
95° 105°
115°
125°
45°
40°
35°
30°
25°
20°
125°
115°
105°
95°
85°
75°
LEGEND
WASHINGTON
OREGON
MONTANA
IDAHO
NEVADA
WYOMING
UTAH
COLORADO
CALIFORNIA
ARIZONA
NEW MEXICO
NORTH
DAKOTA
SOUTH
DAKOTA
NEBRASKA
KANSAS
OKLAHOMA
TEXAS
LA
MS
FL
GEORGIA
SC
MD
DE
RI
ME
VT
NH
MA
CT
NEW YORK
PA
WV
VIRGINA
MI
IN
OHIO
WISCONSIN
MINNESOTA
IOWA
ILLINOIS
MISSOURI
ARKANSAS
KENTUCKY
NJ
NO CAROLINA
TENNESSEE
AL
(NOT DRAWN TO SCALE)
Mountainous
Areas
Nonmountainous
Area
Mountainous
Area
Primary Area
Secondary Area
500 Feet
Total Width
of Secondary
Area
Distance from
Obstacle to
Outer Edge of
Secondary Area
Figure 3-10. Obstacle Clearance - Secondary Area.
When a VHF airway or route terminates at a NAVAID or
fix, the primary area extends beyond that termination
point. Figure 3-11 and its inset show the construction of
the primary and secondary areas at the termination
point. When a change of course on VHF airways and
routes is necessary, the en route obstacle clearance
turning area extends the primary and secondary
obstacle clearance areas to accommodate the turn
radius of the aircraft. Since turns at or after fix passage may exceed airway and route boundaries, pilots
are expected to adhere to airway and route protected
airspace by leading turns early before a fix. The
turn area provides obstacle clearance for both turn
anticipation (turning prior to the fix) and flyover
protection (turning after crossing the fix). This does
not violate the requirement to fly the centerline of the
airway. Many factors enter into the construction and
application of the turning area to provide pilots with
adequate obstacle clearance protection. These may
include aircraft speed, the amount of turn versus
NAVAID distance, flight track, curve radii, MEAs,
and minimum turning altitude (MTA). A typical protected airspace is shown in Figure 3-11. Turning area
system accuracy factors must be applied to the most
adverse displacement of the NAVAID or fix and the
airway or route boundaries at which the turn is made.
If applying nonmountainous en route turning area criteria graphically, depicting the vertical obstruction
clearance in a typical application, the template might
appear as in Figure 3-12 on page 3-10.
Turns that begin at or after fix passage may exceed the
protected en route turning area obstruction clearance.
Figure 3-13 on page 3-10 contains an example of a
flight track depicting a turn at or after fix passage,
together with an example of an early turn. Without
leading a turn, an aircraft operating in excess of 290
knots true airspeed (TAS) can exceed the normal airway or route boundaries depending on the amount of
course change required, wind direction and velocity,
the character of the turn fix (DME, overhead navigation aid, or intersection), and pilot technique in making
a course change. For example, a flight operating at
17,000 feet MSL with a TAS of 400 knots, a 25° bank,
and a course change of more than 40° would exceed the
width of the airway or route; i.e., 4 NM each side of
centerline. Due to the high airspeeds used at 18,000
feet MSL and above, additional IFR separation protection for course changes is provided.
NAVAID SERVICE VOLUME
Each class of VHF NAVAID (VOR/DME/TACAN)
has an established operational service volume to
ensure adequate signal coverage and frequency protection from other NAVAIDs on the same frequency.
The maximum distance at which NAVAIDs are usable
varies with altitude and the class of the facility. When
using VORs for direct route navigation, the following
guidelines apply:
• For operations above FL 450, use aids not more
than 200 NM apart. These are High Altitude (H)
class facilities and are depicted on en route high
altitude charts.
Figure 3-11. Turning Area, Intersection Fix, NAVAID Distance less than 51 NM.
Radii
Center
Secondary
Arcs
Primary
Arcs
Primary
Indexes
"Outside"
"Inside"
Termination
Areas
CENTERLINE
CENTERLINE
En Route
Facility Facility
Providing
Intersection
Radial
Fix
Displacement
Area
4.5°
3.6°
3-9
3-10
• For operations that are off established airways
from 18,000 feet MSL to FL 450, use aids not
more than 260 NM apart. These are High Altitude
(H) class facilities and are depicted on en route
high altitude charts.
• For operations that are off established airways
below 18,000 feet MSL, use aids not more than
80 NM apart. These are Low Altitude (L) class
facilities and are shown on en route low altitude
charts.
• For operations that are off established airways
between 14,500 feet MSL and 17,999 feet MSL
in the conterminous United States, use H-class
facilities not more than 200 NM apart.
The use of satellite based navigation systems has
increased pilot requests for direct routes that take the
aircraft outside ground based NAVAID service volume
limits. These direct route requests are approved only in
a radar environment, and approval is based on pilot
responsibility for staying on the authorized direct route.
ATC uses radar flight following for the purpose of aircraft separation. On the other hand, if ATC initiates a
direct route that exceeds NAVAID service volume limits, ATC also provides radar navigational assistance as
necessary. More information on direct route navigation
is located in the En Route RNAV Procedures section
later in this chapter.
NAVIGATIONAL GAPS
Where a navigational course guidance gap exists,
referred to as an MEA gap, the airway or route segment
may still be approved for navigation. The navigational
gap may not exceed a specific distance that varies
directly with altitude, from zero NM at sea level to 65
NM at 45,000 feet MSL and not more than one gap may
exist in the airspace structure for the airway or route
segment. Additionally, a gap usually does not occur at
any airway or route turning point. To help ensure the
maximum amount of continuous positive course guidance available when flying, there are established en
route criteria for both straight and turning segments.
Where large gaps exist that require altitude changes,
MEA “steps” may be established at increments of not
less than 2,000 feet below 18,000 feet MSL, or not less
than 4,000 feet at 18,000 MSL and above, provided that
a total gap does not exist for the entire segment within
the airspace structure. MEA steps are limited to one
step between any two facilities to eliminate continuous
or repeated changes of altitude in problem areas. The
allowable navigational gaps pilots can expect to see
Secondary Area
Primary Area
500 Feet
500 Feet
Figure 3-12. Turning Area Obstruction Clearance.
Airway Route Boundary
Airway Route Boundary
Turning
Fix
Early Turn
Turn at or after
Fix Passage
Figure 3-13. Adhering to Airway/Route Turning Area.
3-11
are determined, in part, by reference to the graph
depicted in Figure 3-14. Notice the en route chart
excerpt depicting that the MEA is established with a
gap in navigation signal coverage northwest of the
Carbon VOR/DME on V134. At the MEA of 13,000,
the allowable navigation course guidance gap is
approximately 18.5 NM, as depicted by Sample 2. The
navigation gap area is not identified on the chart by
distances from the navigation facilities.
CHANGEOVER POINTS
When flying airways, pilots normally change frequencies midway between navigation aids, although there
are times when this is not practical. If the navigation
signals cannot be received from the second VOR at the
midpoint of the route, a changeover point (COP) is
depicted and shows the distance in NM to each NAVAID,
as depicted in Figure 3-15 on page 3-12. COPs indicate
the point where a frequency change is necessary to
receive course guidance from the facility ahead of the
aircraft instead of the one behind. These changeover
points divide an airway or route segment and ensure
continuous reception of navigation signals at the prescribed minimum en route IFR altitude. They also
ensure that other aircraft operating within the same portion of an airway or route segment receive consistent
azimuth signals from the same navigation facilities
regardless of the direction of flight.
Where signal coverage from two VORs overlaps at the
MEA, the changeover point normally is designated at
the midpoint. Where radio frequency interference or
other navigation signal problems exist, the COP is
placed at the optimum location, taking into consideration the signal strength, alignment error, or any other
known condition that affects reception. The changeover
point has an effect on the primary and secondary obstacle clearance areas. On long airway or route segments,
if the distance between two facilities is over 102 NM
and the changeover point is placed at the midpoint,
the system accuracy lines extend beyond the minimum widths of 8 and 12 NM, and a flare or spreading
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
MEA OF AIRWAY OR
ROUTE SEGMENT
(THOUSANDS OF FEET)
Sample 1: Enter with MEA of 27,000 Feet.
Read Allowable Gap 39 NM
Sample 2: Enter with MEA of 13,000 Feet.
Read Allowable Gap 18.5 NM
ALLOWABLE NAVIGATION COURSE GUIDANCE GAP (NM)
Figure 3-14. Navigational Course Guidance Gaps.
3-12
outward results at the COP, as shown in Figure 3-16.
Offset changeover points and dogleg segments on airways or routes can also result in a flare at the COP.
IFR EN ROUTE ALTITUDES
Minimum en route altitudes, minimum reception altitudes, maximum authorized altitudes, minimum
obstruction clearance altitudes, minimum crossing
altitudes, and changeover points are established by
the FAA for instrument flight along Federal airways,
as well as some off-airway routes. The altitudes are
established after it has been determined that the navigation aids to be used are adequate and so oriented
on the airways or routes that signal coverage is
acceptable, and that flight can be maintained within
prescribed route widths.
For IFR operations, regulations require that pilots operate their aircraft at or above minimum altitudes. Except
when necessary for takeoff or landing, pilots may not
operate an aircraft under IFR below applicable minimum altitudes, or if no applicable minimum altitude is
prescribed, in the case of operations over an area designated as mountainous, an altitude of 2,000 feet above
the highest obstacle within a horizontal distance of 4 NM
from the course to be flown. In any other case, an altitude
of 1,000 feet above the highest obstacle within a horizontal distance of 4 NM from the course to be flown must be
maintained as a minimum altitude. If both a MEA and a
minimum obstruction clearance altitude (MOCA) are
prescribed for a particular route or route segment, pilots
may operate an aircraft below the MEA down to, but not
below, the MOCA, only when within 22 NM of the VOR.
When climbing to a higher minimum IFR altitude (MIA),
pilots must begin climbing immediately after passing the
point beyond which that minimum altitude applies,
except when ground obstructions intervene, the point
beyond which that higher minimum altitude applies must
be crossed at or above the applicable minimum crossing
altitude (MCA) for the VOR.
If on an IFR flight plan, but cleared by ATC to maintain
VFR conditions on top, pilots may not fly below minimum en route IFR altitudes. Minimum altitude rules
are designed to ensure safe vertical separation between
the aircraft and the terrain. These minimum altitude
rules apply to all IFR flights, whether in IFR or VFR
Figure 3-16. Changeover Point Effect on Long Airway or Route Segment.
4 NM
4 NM
2 NM
2 NM
6.7°
4.5°
4.5°
6.7°
70
70
Secondary Areas
Primary Area
Flare
Flare
Figure 3-15. Changeover Points.
22
45
13,000 ft
13,000
V 344
3-13
weather conditions, and whether assigned a specific
altitude or VFR conditions on top.
MINIMUM EN ROUTE ALTITUDE
The minimum enroute altitude (MEA) is the lowest
published altitude between radio fixes that assures
acceptable navigational signal coverage and meets
obstacle clearance requirements between those fixes.
The MEA prescribed for a Federal airway or segment,
RNAV low or high route, or other direct route applies
to the entire width of the airway, segment, or route
between the radio fixes defining the airway, segment,
or route. MEAs for routes wholly contained within
controlled airspace normally provide a buffer above the
floor of controlled airspace consisting of at least 300
feet within transition areas and 500 feet within control
areas. MEAs are established based upon obstacle clearance over terrain and manmade objects, adequacy of
navigation facility performance, and communications
requirements, although adequate communication at the
MEA is not guaranteed.
MINIMUM OBSTRUCTION
CLEARANCE ALTITUDE
The minimum obstruction clearance altitude (MOCA)
is the lowest published altitude in effect between fixes
on VOR airways, off-airway routes, or route segments
that meets obstacle clearance requirements for the entire
route segment. This altitude also assures acceptable navigational signal coverage only within 22 NM of a VOR.
The MOCA seen on the NACO en route chart, may have
been computed by adding the required obstacle clearance (ROC) to the controlling obstacle in the primary
area or computed by using a TERPS chart if the controlling obstacle is located in the secondary area. This figure
is then rounded to the nearest 100 - foot increment, i.e.,
2,049 feet becomes 2,000, and 2,050 feet becomes 2,100
feet. An extra 1,000 feet is added in mountainous areas,
in most cases. The MOCA is based upon obstacle clearance over the terrain or over manmade objects, adequacy
of navigation facility performance, and communications
requirements.
ATC controllers have an important role in helping pilots
remain clear of obstructions. Controllers are instructed
to issue a safety alert if the aircraft is in a position that, in
their judgment, places the pilot in unsafe proximity to
terrain, obstructions, or other aircraft. Once pilots inform
ATC of action being taken to resolve the situation, the
controller may discontinue the issuance of further alerts.
A typical terrain/obstruction alert may sound like this:
“Low altitude alert. Check your altitude immediately.
The MOCA in your area is 12,000.”
MINIMUM VECTORING ALTITUDES
Minimum vectoring altitudes (MVAs) are established
for use by ATC when radar ATC is exercised. The MVA
provides 1,000 feet of clearance above the highest
obstacle in nonmountainous areas and 2,000 feet above
the highest obstacle in designated mountainous areas.
Because of the ability to isolate specific obstacles, some
MVAs may be lower than MEAs, MOCAs, or other
minimum altitudes depicted on charts for a given
location. While being radar vectored, IFR altitude
assignments by ATC are normally at or above the
MVA.
Controllers use MVAs only when they are assured an
adequate radar return is being received from the aircraft. Charts depicting minimum vectoring altitudes
are normally available to controllers but not available
to pilots. Situational awareness is always important,
especially when being radar vectored during a climb
into an area with progressively higher MVA sectors,
similar to the concept of minimum crossing altitude.
Except where diverse vector areas have been established, when climbing, pilots should not be vectored
into a sector with a higher MVA unless at or above the
next sector’s MVA. Where lower MVAs are required
in designated mountainous areas to achieve compatibility with terminal routes or to permit vectoring to an
instrument approach procedure, 1,000 feet of obstacle
clearance may be authorized with the use of Airport
Surveillance Radar (ASR). The MVA will provide at
least 300 feet above the floor of controlled airspace.
The MVA charts are developed to the maximum radar
range. Sectors provide separation from terrain and
obstructions. Each MVA chart has sectors large
enough to accommodate vectoring of aircraft within
the sector at the MVA.
MINIMUM RECEPTION ALTITUDE
Minimum reception altitudes (MRAs) are determined by FAA flight inspection traversing an entire
route of flight to establish the minimum altitude the
navigation signal can be received for the route and
for off-course NAVAID facilities that determine a fix.
When the MRA at the fix is higher than the MEA, an
MRA is established for the fix, and is the lowest altitude at which an intersection can be determined.
MINIMUM CROSSING ALTITUDE
A minimum crossing altitude (MCA) is the lowest altitude at certain fixes at which the aircraft must cross when
proceeding in the direction of a higher minimum en route
IFR altitude, as depicted in Figure 3-18 on page 3-14.
MCAs are established in all cases where obstacles intervene to prevent pilots from maintaining obstacle clearance
during a normal climb to a higher MEA after passing a
point beyond which the higher MEA applies. The same
protected en route area vertical obstacle clearance requirements for the primary and secondary areas are considered
in the determination of the MCA. The standard for determining the MCA is based upon the following climb
gradients, and is computed from the flight altitude:
• Sea level through 5,000 feet MSL—150 feet per
NM
3-14
Figure 3-17. Example of an Air Route Traffic Control Center MVA Chart.
10,000
RIW
15,800
14,500
12,000
13,700
10,700
11,000
12,400
12,000
15,500
14,200
11,000
13,800
13,300
12,300
CKW
VEL
FBR
RKS
RKS 325
RKS 003
070
065
243
RKS 269
211
RKS 080
270
001
065
110
180
RKS 160
20
40
60
80
100
120
14,500
0 00
70
00 0
2, 2, 00
142
14
5
C
00 0
X
V 361
5900
V 361
5200
V 361 5900 E
SQWID
Figure 3-18. Minimum Crossing Altitude.
3-15
• 5000 feet through 10,000 feet MSL — 120 feet
per NM
• 10,000 feet MSL and over — 100 feet per NM
To determine the MCA seen on a NACO en route
chart, the distance from the obstacle to the fix is computed from the point where the centerline of the en
route course in the direction of flight intersects the
farthest displacement from the fix, as shown in Figure
3-19. When a change of altitude is involved with a
course change, course guidance must be provided if
the change of altitude is more than 1,500 feet and/or if
the course change is more than 45 degrees, although
there is an exception to this rule. In some cases, course
changes of up to 90 degrees may be approved without
course guidance provided that no obstacles penetrate
the established MEA requirement of the previous airway or route segment. Outside U. S. airspace, pilots
may encounter different flight procedures regarding
MCA and transitioning from one MEA to a higher
MEA. In this case, pilots are expected to be at the higher
MEA crossing the fix, similar to an MCA. Pilots must
thoroughly review flight procedure differences when flying outside U.S. airspace. On NACO en route charts,
routes and associated data outside the conterminous U.S.
are shown for transitional purposes only and are not part
of the high altitude jet route and RNAV route systems.
Figure 3-19. MCA Determination Point.
3200'
700'
2000'
2000'
6 NM
4620' MSL
120' per NM Required
Multiply by 6 NM -720 Ft.
Maximum Displacement
MSL
Obstacle Line
Obstruction Height 4620'
Required Clearance +2000'
MOCA At Obstruction = 6620'
Climb Value* - 720'
MCA Required = 5900'
* Based upon 6 NM @ 120 Feet Per NM
X
MEA 5200'
MCA 5900' E
Figure 3-20. Crossing a Fix to a Higher MEA in Canada.
3-16
MAXIMUM AUTHORIZED ALTITUDE
A maximum authorized altitude (MAA) is a published
altitude representing the maximum usable altitude or
flight level for an airspace structure or route segment. It
is the highest altitude on a Federal airway, jet route,
RNAV low or high route, or other direct route for which
an MEA is designated at which adequate reception of
navigation signals is assured. MAAs represent procedural limits determined by technical limitations or other
factors such as limited airspace or frequency interference of ground based facilities.
IFR CRUISING ALTITUDE OR FLIGHT LEVEL
In controlled airspace, pilots must maintain the altitude
or flight level assigned by ATC, although if the ATC
clearance assigns “VFR conditions on-top,” an altitude
or flight level as prescribed by Part 91.159 must be
maintained. In uncontrolled airspace (except while in a
holding pattern of 2 minutes or less or while turning) if
operating an aircraft under IFR in level cruising flight,
an appropriate altitude as depicted in the legend of
NACO IFR en route high and low altitude charts must
be maintained.
When operating on an IFR flight plan below 18,000 feet
MSL in accordance with a VFR-on-top clearance, any
VFR cruising altitude appropriate to the direction of
flight between the MEA and 18,000 feet MSL may be
selected that allows the flight to remain in VFR conditions. Any change in altitude must be
reported to ATC and pilots must comply
with all other IFR reporting procedures.
VFR-on-top is not authorized in Class A
airspace. When cruising below 18,000
feet MSL, the altimeter must be adjusted
to the current setting, as reported by a
station within 100 NM of your position.
In areas where weather-reporting stations are more than 100 NM from the
route, the altimeter setting of a station
that is closest may be used. During IFR
flight, ATC advises flights periodically
of the current altimeter setting, but it
remains the responsibility of the pilot or
flight crew to update altimeter settings
in a timely manner. Altimeter settings
and weather information are available
from weather reporting facilities operated or approved by the U.S. National
Weather Service, or a source approved
by the FAA. Some commercial operators have the authority to act as a
government-approved source of
weather information, including
altimeter settings, through certification under the FAA’s Enhanced
Weather Information System.
Flight level operations at or above 18,000 feet MSL
require the altimeter to be set to 29.92. A flight level
(FL) is defined as a level of constant atmospheric pressure related to a reference datum of 29.92 in. Hg. Each
flight level is stated in three digits that represent hundreds of feet. For example, FL 250 represents an
altimeter indication of 25,000 feet. Conflicts with
traffic operating below 18,000 feet MSL may arise
when actual altimeter settings along the route of flight
are lower than 29.92. Therefore, Part 91.121 specifies
the lowest usable flight levels for a given altimeter
setting range.
LOWEST USABLE FLIGHT LEVEL
When the barometric pressure is 31.00 inches of mercury or less and pilots are flying below 18,000 feet
MSL, use the current reported altimeter setting. This is
important because the true altitude of an aircraft is
lower than indicated when sea level pressure is lower
than standard. When an aircraft is en route on an instrument flight plan, air traffic controllers furnish this
information at least once while the aircraft is in the controller’s area of jurisdiction. According to Part 91.144,
when the barometric pressure exceeds 31.00 inches
Hg., the following procedures are placed in effect by
NOTAM defining the geographic area affected: Set
31.00 inches for en route operations below 18,000 feet
MSL and maintain this setting until beyond the affected
area. Air traffic control issues actual altimeter settings
Figure 3-21. IFR Cruising Altitude or Flight Level.
3-17
and advises pilots to set 31.00 inches in their altimeter,
for en route operations below 18,000 feet MSL in
affected areas. If an aircraft has the capability of setting
the current altimeter setting and operating into airports
with the capability of measuring the current altimeter
setting, no additional restrictions apply. At or above
18,000 feet MSL, altimeters should be set to 29.92
inches of mercury (standard setting). Additional procedures exist beyond the en route phase of flight.
The lowest usable flight level is determined by the
atmospheric pressure in the area of operation. As local
altimeter settings fall below 29.92, pilots operating in
Class A airspace must cruise at progressively higher
indicated altitudes to ensure separation from aircraft
operating in the low altitude structure as follows:
Current Altimeter Setting Lowest Usable
Flight Level
• 29.92 or higher 180
• 29.91 to 29.42 185
• 29.41 to 28.92 190
• 28.91 to 28.42 195
• 28.41 to 27.92 200
When the minimum altitude, as prescribed in Parts
91.159 and 91.177, is above 18,000 feet MSL, the lowest usable flight level is the flight level equivalent of
the minimum altitude plus the number of feet specified
according to the lowest flight level correction factor as
follows:
Altimeter Setting Correction Factor
• 29.92 or higher none
• 29.91 to 29.42 500 Feet
• 29.41 to 28.92 1000 Feet
• 28.91 to 28.42 1500 Feet
• 28.41 to 27.92 2000 Feet
• 27.91 to 27.42 2500 Feet
OPERATIONS IN OTHER COUNTRIES
When flight crews transition from the U.S. NAS to
another country’s airspace, they should be aware of differences not only in procedures but also airspace. For
example, when flying into Canada regarding altimeter
setting changes, as depicted in Figure 3-22 on page 3-18,
notice the change from QNE to QNH when flying northbound into the Moncton flight information region
(FIR), an airspace of defined dimensions where flight
information service and alerting service are provided.
Transition altitude (QNH) is the altitude in the vicinity
of an airport at or below which the vertical position of
the aircraft is controlled by reference to altitudes (MSL).
The transition level (QNE) is the lowest flight level
available for use above the transition altitude. Transition
height (QFE) is the height in the vicinity of an airport at
or below which the vertical position of the aircraft is
expressed in height above the airport reference datum.
The transition layer is the airspace between the transition altitude and the transition level. If descending
through the transition layer, set the altimeter to local station pressure. When departing and climbing through the
transition layer, use the standard altimeter setting (QNE)
of 29.92 inches of Mercury, 1013.2 millibars, or 1013.2
hectopascals. Remember that most pressure altimeters
are subject to mechanical, elastic, temperature, and
installation errors. Extreme cold temperature differences
also may require a correction factor.
REPORTING PROCEDURES
In addition to acknowledging a handoff to another
Center en route controller, there are reports that should
be made without a specific request from ATC. Certain
reports should be made at all times regardless of
whether a flight is in radar contact with ATC, while
others are necessary only if radar contact has been lost
or terminated. Refer to Figure 3-23 on page 3-19 for a
review of these reports.
NONRADAR POSITION REPORTS
If radar contact has been lost or radar service terminated, the CFRs require pilots to provide ATC
with position reports over designated VORs and
intersections along their route of flight. These
compulsory reporting points are depicted on
NACO IFR en route charts by solid triangles.
Position reports over fixes indicated by open triangles are noncompulsory reporting points, and are
only necessary when requested by ATC. If on a
direct course that is not on an established airway,
report over the fixes used in the flight plan that
define the route, since they automatically become
compulsory reporting points. Compulsory reporting points also apply when conducting an IFR
flight in accordance with a VFR-on-top clearance.
Whether a route is on airways or direct, position
reports are mandatory in a nonradar environment,
and they must include specific information. A typical
position report includes information pertaining to aircraft position, expected route, and estimated time
of arrival (ETA). Time may be stated in minutes
only when no misunderstanding is likely to occur.
3-18
COMMUNICATION FAILURE
Two-way radio communication failure procedures for
IFR operations are outlined in Part 91.185. Unless otherwise authorized by ATC, pilots operating under IFR are
expected to comply with this regulation. Expanded procedures for communication failures are found in the
AIM. Pilots can use the transponder to alert ATC to a
radio communication failure by squawking code 7600.
If only the transmitter is
inoperative, listen for ATC instructions on any operational receiver, including the navigation receivers. It is
possible ATC may try to make contact with pilots over a
VOR, VORTAC, NDB, or localizer frequency. In addition
to monitoring NAVAID receivers, attempt to reestablish
communications by contacting ATC on a previously
assigned frequency, calling a FSS or Aeronautical Radio
Incorporated (ARINC).
The primary objective of the regulations governing communication failures is to preclude extended IFR no-radio
operations within the ATC system since these operations
may adversely affect other users of the airspace. If the
radio fails while operating on an IFR clearance, but in
VFR conditions, or if encountering VFR conditions at
any time after the failure, continue the flight under VFR
conditions, if possible, and land as soon as practicable.
The requirement to land as soon as practicable should
not be construed to mean as soon as possible. Pilots
retain the prerogative of exercising their best judgment
and are not required to land at an unauthorized airport, at
an airport unsuitable for the type of aircraft flown, or to
land only minutes short of their intended destination.
However, if IFR conditions prevail, pilots must comply
with procedures designated in the CFRs to ensure aircraft separation.
If pilots must continue their flight under IFR after experiencing two-way radio communication failure, they
should fly one of the following routes:
• The route assigned by ATC in the last clearance
received.
Figure 3-22. Altimeter Setting Changes.
3-19
• If being radar vectored, the direct route from the
point of radio failure to the fix, route, or airway
specified in the radar vector clearance.
• In the absence of an assigned route, the route ATC
has advised to expect in a further clearance.
• In the absence of an assigned or expected route,
the route filed in the flight plan.
It is also important to fly a specific altitude should
two-way radio communications be lost. The altitude
to fly after a communication failure can be found in
Part 91.185 and must be the highest of the following
altitudes for each route segment flown.
• The altitude or flight level assigned in the last
ATC clearance.
• The minimum altitude or flight level for IFR
operations.
• The altitude or flight level ATC has advised to
expect in a further clearance.
In some cases, the assigned or expected altitude may
not be as high as the MEA on the next route segment.
In this situation, pilots normally begin a climb to the
higher MEA when they reach the fix where the MEA
rises. If the fix also has a published minimum crossing altitude, they start the climb so they will be at or
above the MCA when reaching the fix. If the next
succeeding route segment has a lower MEA, descend
to the applicable altitude ⎯ either the last assigned
altitude or the altitude expected in a further clearance
⎯ when reaching the fix where the MEA decreases.
Figure 3-23. ATC Reporting Procedure Examples.
Leaving one assigned flight altitude or flight level for another
VFR-on-top change in altitude
Leaving any assigned holding fix or point
Missed approach
Unable to climb or descend at least 500 feet per minute
TAS variation from filed speed of 5% or 10 knots, whichever
is greater
Time and altitude or flight level upon reaching a holding fix
or clearance limit
Loss of nav/comm capability (required by Part 91.187)
Unforecast weather conditions or other information relating
to the safety of flight (required by Part 91.183)
"Marathon 564, leaving 8,000, climb to 10,000."
"Marathon 564, VFR-on-top, climbing to 10,500."
"Marathon 564, leaving FARGO Intersection."
"Marathon 564, missed approach, request clearance to
Chicago."
"Marathon 564, maximum climb rate 400 feet per minute."
"Marathon 564, advises TAS decrease to140 knots."
"Marathon 564, FARGO Intersection at 05, 10,000,
holding east."
"Marathon 564, ILS receiver inoperative."
"Marathon 564, experiencing moderate turbulence
at 10,000."
Leaving FAF or OM inbound on final approach
Revised ETA of more than three minutes
Position reporting at compulsory reporting points (required
by Part 91.183)
"Marathon 564, outer marker inbound, leaving 2,000."
"Marathon 564, revising SCURRY estimate to 55."
See Figure 3-24 on page 3-20 for position report items.
RADAR/NONRADAR REPORTS
These reports should be made at all times without a specific ATC request.
NONRADAR REPORTS
When you are not in radar contact, these reports should be made without a specific request from ATC.
REPORTS EXAMPLE:
REPORTS EXAMPLE:
3-20
CLIMBING AND
DESCENDING EN ROUTE
Before the days of nationwide radar coverage, en route
aircraft were separated from each other primarily by
specific altitude assignments and position reporting
procedures. Much of the pilot’s time was devoted to
inflight calculations, revising ETAs, and relaying
position reports to ATC. Today, pilots and air traffic
controllers have far more information and better tools
to make inflight computations and, with the expansion of radar, including the use of an en route flight
progress strip shown in Figure 3-26, position reports
may only be necessary as a backup in case of radar
failure or for RNAV random route navigation. Figure
3-26 also depicts the numerous en route data entries
used on a flight progress strip, generated by the
ARTCC computer. Climbing, level flight, and
descending during the en route phase of IFR flight
involves staying in communication with ATC, making necessary reports, responding to clearances,
monitoring position, and staying abreast of any
changes to the airplane’s equipment status or weather.
PILOT/CONTROLLER EXPECTATIONS
When ATC issues a clearance or instruction, pilots are
expected to execute its provisions upon receipt. In some
cases, ATC includes words that modify their expectation.
For example, the word “immediately” in a clearance or
instruction is used to impress urgency to avoid an imminent situation, and expeditious compliance is expected
and necessary for safety. The addition of a climb point
or time restriction, for example, does not authorize
pilots to deviate from the route of flight or any other
provision of the ATC clearance. If you receive a term
Identification
Position
Time
Altitude/Flight Level
IFR or VFR (in a report to an FSS only)
ETA over the next reporting fix
Following reporting point
Pertinent remarks
"Marathon 564,
Sidney
15, (minutes after the hour)
9,000,
IFR,
Akron 35, (minutes after the hour)
Thurman next."
(If necessary)
Figure 3-24. Nonradar Position Reports.
Figure 3-25. Two-Way Radio Communication Failure
Transponder Code.
When an aircraft squawks code 7600 during a two-way radio
communication failure, the information block on the radar screen
flashes RDOF (radio failure) to alert the controller.
3-21
“climb at pilot’s discretion” in the altitude information
of an ATC clearance, it means that you have the option
to start a climb when you wish, that you are authorized
to climb at any rate, and to temporarily level off at any
intermediate altitude as desired, although once you
vacate an altitude, you may not return to that altitude.
When ATC has not used the term “at pilot’s discretion”
nor imposed any climb restrictions, you should climb
promptly on acknowledgment of the clearance. Climb
at an optimum rate consistent with the operating characteristics of your aircraft to 1,000 feet below the
assigned altitude, and then attempt to climb at a rate of
Figure 3-26. En Route Flight Progress Strip and Data Entries.
3-22
between 500 and 1,500 feet per minute until you reach
your assigned altitude. If at anytime you are unable to
climb at a rate of at least 500 feet a minute, advise ATC.
If it is necessary to level off at an intermediate altitude
during climb, advise ATC.
“Expedite climb” normally indicates you should use
the approximate best rate of climb without an exceptional change in aircraft handling characteristics.
Normally controllers will inform you of the reason for
an instruction to expedite. If you fly a turbojet airplane
equipped with afterburner engines, such as a military
aircraft, you should advise ATC prior to takeoff if you
intend to use afterburning during your climb to the en
route altitude. Often, the controller may be able to plan
traffic to accommodate a high performance climb and
allow you to climb to the planned altitude without
restriction. If you receive an “expedite” clearance from
ATC, and your altitude to maintain is subsequently
changed or restated without an expedite instruction, the
expedite instruction is canceled.
During en route climb, as in any other phase of
flight, it is essential that you clearly communicate
with ATC regarding clearances. In the following
example, a flight crew experienced an apparent
clearance readback/hearback error, that resulted in
confusion about the clearance, and ultimately, to
inadequate separation from another aircraft.
“Departing IFR, clearance was to maintain 5,000
feet, expect 12,000 in ten minutes. After handoff to
Center, we understood and read back, ‘Leaving
5,000 turn left heading 240° for vector on course.’
The First Officer turned to the assigned heading
climbing through 5,000 feet. At 5,300 feet Center
advised assigned altitude was 5,000 feet. We immediately descended to 5,000. Center then informed us
we had traffic at 12 o’clock and a mile at 6,000. After
passing traffic, a higher altitude was assigned and
climb resumed. We now believe the clearance was
probably ‘reaching’ 5,000, etc. Even our readback to the
controller with ‘leaving’ didn’t catch the different wording.” “Reaching” and “leaving” are commonly used ATC
terms having different usages. They may be used in
clearances involving climbs, descents, turns, or speed
changes. In the cockpit, the words “reaching” and “leaving” sound much alike.
For altitude awareness during climb, professional pilots
often call out altitudes on the flight deck. The pilot
monitoring may call 2,000 and 1,000 feet prior to
reaching an assigned altitude. The callout may be, “two
to go” and “one to go.” Climbing through the transition altitude (QNH), both pilots set their altimeters to
29.92 inches of mercury and announce “2992 inches”
(or ‘standard,’ on some airplanes) and the flight level
passing. For example, “2992 inches” (‘standard’),
flight level one eight zero.” The second officer on three
pilot crews may ensure that both pilots have inserted
the proper altimeter setting. On international flights,
pilots must be prepared to differentiate, if necessary,
between barometric pressure equivalents with inches
of mercury, and millibars or hectopascals, to eliminate any potential for error, for example, 996 millibars
erroneously being set as 2996.
For a typical IFR flight, the majority of inflight time
often is flown in level flight at cruising altitude, from top
of climb to top of descent (TOD). Generally, TOD is
used in airplanes with a flight management system
(FMS), and represents the point at which descent is first
initiated from cruise altitude. FMSs also assist in level
flight by cruising at the most fuel saving speed, providing continuing guidance along the flight plan route,
including great circle direct routes, and continuous evaluation and prediction of fuel consumption along with
changing clearance data. Descent planning is discussed
in more detail in the next chapter, “Arrivals.”
AIRCRAFT SPEED AND ALTITUDE
During the en route descent phase of flight, an additional benefit of flight management systems is that the
FMS provides fuel saving idle thrust descent to your
destination airport. This allows an uninterrupted profile
descent from level cruising altitude to an appropriate minimum IFR altitude (MIA), except where
level flight is required for speed adjustment.
Controllers anticipate and plan that you may level off at
10,000 feet MSL on descent to comply with the Part 91
indicated airspeed limit of 250 knots. Leveling off at
any other time on descent may seriously affect air traffic handling by ATC. It is imperative that you make
every effort to fulfill ATC expected actions on descent
to aid in safely handling and expediting air traffic.
ATC issues speed adjustments if you are being radar
controlled to achieve or maintain required or desired
spacing. They express speed adjustments in terms of
knots based on indicated airspeed in 10 knot increments except that at or above FL 240 speeds may be
expressed in terms of Mach numbers in 0.01 increments. The use of Mach numbers by ATC is restricted
to turbojets. If complying with speed adjustments,
pilots are expected to maintain that speed within plus
or minus 10 knots or 0.02 Mach.
Speed and altitude restrictions in clearances are subject
to misinterpretation, as evidenced in this case where a
corporate flight crew treated instructions in a published
procedure as a clearance. “…We were at FL 310 and
had already programmed the ‘expect-crossing 慬瑩瑵摥
3-23
of 17,000 feet at the VOR. When the altitude alerter
sounded, I advised Center that we were leaving FL 310.
ATC acknowledged with a ‘Roger.’ At FL 270, Center
quizzed us about our descent. I told the controller we
were descending so as to cross the VOR at 17,000 feet.
ATC advised us that we did not have clearance to
descend. What we thought was a clearance was in fact
an ‘expect’ clearance. We are both experienced
pilots…which just means that experience is no substitute for a direct question to Center when you are in
doubt about a clearance. Also, the term ‘Roger’ only
means that ATC received the transmission, not that they
understood the transmission. The AIM indicates that
‘expect’ altitudes are published for planning purposes.
‘Expect’ altitudes are not considered crossing restrictions until verbally issued by ATC.”
HOLDING PROCEDURES
The criteria for holding pattern airspace is developed
both to provide separation of aircraft, as well as obstacle
clearance The alignment of holding patterns typically
coincides with the flight course you fly after leaving the
holding fix. For level holding, a minimum of 1,000 feet
obstacle clearance is provided throughout the primary
area. In the secondary area 500 feet of obstacle clearance
is provided at the inner edge, tapering to zero feet at the
outer edge. Allowance for precipitous terrain is considered, and the altitudes selected for obstacle clearance
may be rounded to the nearest 100 feet. When criteria for
a climb in hold are applied, no obstacle penetrates the
holding surface.
There are many factors that affect aircraft during holding maneuvers, including navigational aid ground and
airborne tolerance, effect of wind, flight procedures,
application of air traffic control, outbound leg length,
maximum holding airspeeds, fix to NAVAID distance,
DME slant range effect, holding airspace size, and
altitude holding levels. In order to allow for these factors when establishing holding patterns, procedure
specialists must apply complex criteria contained in
Order 7130.3, Holding Pattern Criteria.
ATC HOLDING INSTRUCTIONS
When controllers anticipate a delay at a clearance limit
or fix, pilots will usually be issued a holding clearance
at least five minutes before the ETA at the clearance
limit or fix. If the holding pattern assigned by ATC is
depicted on the appropriate aeronautical chart, pilots
are expected to hold as published. In this situation, the
controller will issue a holding clearance which includes
the name of the fix, directs you to hold as published,
Figure 3-27. Typical Holding Pattern Design Criteria Template.
Fix Displacement Area
Facility
Facility
Secondary Area
Primary Area
Holding Pattern Airspace Area
3-24
and includes an expect further clearance (EFC) time.
An example of such a clearance is: “Marathon five
sixty four, hold east of MIKEY Intersection as published, expect further clearance at 1521.” When ATC
issues a clearance requiring you to hold at a fix where a
holding pattern is not charted, you will be issued complete holding instructions. This information includes
the direction from the fix, name of the fix, course, leg
length, if appropriate, direction of turns (if left turns
are required), and the EFC time. You are required to
maintain your last assigned altitude unless a new altitude is specifically included in the holding clearance,
and you should fly right turns unless left turns are
assigned. Note that all holding instructions should
include an EFC time. If you lose two-way radio communication, the EFC allows you to depart the holding
fix at a definite time. Plan the last lap of your holding
pattern to leave the fix as close as possible to the exact
time.
If you are approaching your clearance limit and have
not received holding instructions from ATC, you are
expected to follow certain procedures. First, call ATC
and request further clearance before you reach the fix.
If you cannot obtain further clearance, you are expected
to hold at the fix in compliance with the published
holding pattern. If a holding pattern is not charted at
the fix, you are expected to hold on the inbound course
using right turns. This procedure ensures that ATC will
provide adequate separation. Assume you
are eastbound on V214 and the Cherrelyn VORTAC is
your clearance limit. If you have not been able to obtain
further clearance and have not received holding instructions, you should plan to hold southwest on the 221
degrees radial using left-hand turns, as depicted. If this
holding pattern was not charted, you would hold west
of the VOR on V214 using right-hand turns.
Where required for aircraft separation, ATC may
request that you hold at any designated reporting point
in a standard holding pattern at the MEA or the MRA,
whichever altitude is the higher at locations where a
minimum holding altitude has not been established.
Unplanned holding at en route fixes may be expected
on airway or route radials, bearings, or courses. If the
fix is a facility, unplanned holding could be on any
radial or bearing. There may be holding limitations
required if standard holding cannot be accomplished at
the MEA or MRA.
MAXIMUM HOLDING SPEED
As you have seen, the size of the holding pattern is
directly proportional to the speed of the airplane. In
order to limit the amount of airspace that must be protected by ATC, maximum holding speeds in knots
Figure 3-28. ATC Holding Instructions.
A clearance for an uncharted holding pattern contains additional information:
There are at least three items in a
clearance for a charted holding pattern:
• Direction to hold from the holding fix
• Holding fix
• Expect further clearance time
"...Hold southeast
of PINNE Intersection as published.
Expect further clearance at 1645."
• Direction to hold from holding fix
• Holding fix
• The holding course (a specified radial, magnetic bearing, airway or route number)
• The outbound leg length in minutes or nautical miles when DME is used
• Nonstandard pattern, if used
• Expect further clearance time
"...Hold west
of Horst Intersection
on Victor 8
5 mile legs
left turns
expect further clearance at 1430."
3-25
indicated airspeed (KIAS) have been designated for
specific altitude ranges . Even so, some
holding patterns may have additional speed restrictions
to keep faster airplanes from flying out of the protected
area. If a holding pattern has a nonstandard speed
restriction, it will be depicted by an icon with the limiting airspeed. If the holding speed limit is less than you
feel is necessary, you should advise ATC of your
revised holding speed. Also, if your indicated airspeed
exceeds the applicable maximum holding speed, ATC
expects you to slow to the speed limit within three minutes of your ETA at the holding fix. Often pilots can
avoid flying a holding pattern, or reduce the length of
time spent in the holding pattern, by slowing down on
the way to the holding fix.
HIGH PERFORMANCE
HOLDING
Certain limitations come into
play when you operate at higher
speeds; for instance, aircraft do
not make standard rate turns in
holding patterns if the bank
angle will exceed 30 degrees. If
your aircraft is using a flight
director system, the bank angle
is limited to 25 degrees. Since
any aircraft must be traveling at
over 210 knots TAS for the bank
angle in a standard rate turn to
exceed 30 degrees, this limit
applies to relatively fast airplanes. An aircraft using a flight
director would have to be holding at more than 170 knots TAS
to come up against the 25
degrees limit. These true airspeeds correspond to indicated
airspeeds of about 183 and 156
knots, respectively, at 6,000
feet in a standard atmosphere
.
Since some military airplanes
need to hold at higher speeds than the
civilian limits, the maximum at military
airfields is higher. For example, the
maximum holding airspeed at USAF
airfields is 310 KIAS.
FUEL STATE AWARENESS
In order to increase fuel state awareness,
commercial operators and other professional flight crews are required to record
the time and fuel remaining during IFR
flight. For example, on a flight scheduled
for one hour or less, the flight crew may
record the time and fuel remaining at the
top of climb (TOC) and at one additional
waypoint listed in the flight plan.
Generally, TOC is used in airplanes with a flight management system, and represents the point at which
cruise altitude is first reached. TOC is calculated based
on current airplane altitude, climb speed, and cruise
altitude. The captain may elect to delete the additional
waypoint recording requirement if the flight is so short
that the record will not assist in the management of the
flight. For flights scheduled for more than one hour, the
flight crew may record the time and fuel remaining
shortly after the top of climb and at selected waypoints
listed in the flight plan, conveniently spaced approximately one hour apart. The flight crew compares
actual fuel burn to planned fuel burn. Each fuel tank
must be monitored to verify proper burn off and
appropriate fuel remaining. On two pilot airplanes,
CHERRELYN
D
( H )117.2 CHL
V214
331°
269°
221°
126°
Figure 3-29. Clearance Limit Holding.
Figure 3-30. Maximum Holding Speed Examples.
Maximum Holding Airspeed: 200 KIAS
14,000'
MSL
6,000'
MSL
Maximum Holding Airspeed: 265 KIAS
Maximum Holding Airspeed: 230 KIAS
Minimum
Holding
Altitude
(MHA)
6,001'
MSL
14,001'
MSL
3-26
the pilot monitoring (PM) keeps the flight plan record.
On three pilot airplanes, the second officer and PM
coordinate recording and keeping the flight plan
record. In all cases, the pilot making the recording
communicates the information to the pilot flying.
DIVERSION PROCEDURES
Operations Specifications (OpsSpecs) for commercial
operators include provisions for en route emergency
diversion airport requirements. Operators are expected
to develop a sufficient set of emergency diversion airports, such that one or more can be reasonably
expected to be available in varying weather conditions. The flight must be able to make a safe landing,
and the airplane maneuvered off of the runway at the
selected diversion airport. In the event of a disabled
airplane following landing, the capability to move the
disabled airplane must exist so as not to block the
operation of any recovery airplane. In addition, those
airports designated for use must be capable of protecting the safety of all personnel by being able to:
• Offload the passengers and flight crew in a safe
manner during possible adverse weather conditions.
• Provide for the physiological needs of the passengers and flight crew for the duration until safe
evacuation.
• Be able to safely extract passengers and flight
crew as soon as possible. Execution and completion of the recovery is expected within 12 to 48
hours following diversion.
Part 91 operators also need to be prepared for a diversion. Designation of an alternate in the IFR flight
plan is a good first step; although, changing weather
conditions or equipment issues may require pilots to
consider other options.
EN ROUTE RNAV PROCEDURES
RNAV is a method of navigation that permits aircraft
operations on any desired course within the coverage
of station-referenced signals, or within the limits of
self-contained system capability. The continued growth
in aviation creates increasing demands on airspace
capacity and emphasizes the need for optimum utilization of available airspace. These factors, allied with the
requirement for NAS operational efficiency, along with
the enhanced accuracy of current navigation systems,
resulted in the required navigation performance (RNP)
concept. RNAV is incorporated into RNP requirements.
OFF AIRWAY ROUTES
Part 95 prescribes altitudes governing the operation of
your aircraft under IFR on Federal airways, jet routes,
RNAV low or high altitude routes, and other direct
routes for which an MEA is designated in this regulation. In addition, it designates mountainous areas and
changeover points. Off-airway routes are established
in the same manner, and in accordance with the same
criteria as airways and jet routes. If you fly for a scheduled air carrier or operator for compensation or hire,
any requests for the establishment of off-airway routes
are initiated by your company through your principal
operations inspector (POI) who works directly with
your company and coordinates FAA approval. Air carrier authorized routes are contained in the company’s
OpsSpecs under the auspices of the air carrier operating certificate.
Off-airway routes predicated on public navigation
facilities and wholly contained within controlled airspace are published as direct Part 95 routes. Off-airway
routes predicated on privately owned navigation facilities or not contained wholly within controlled airspace
are published as off-airway non-Part 95 routes. In evaluating the adequacy of off-airway routes, the following
items are considered; the type of aircraft and navigation systems used; proximity to military bases, training
areas, low level military routes; and the adequacy of
communications along the route. If you are a commercial operator, and you plan to fly off-airway routes,
your OpsSpecs will likely address en route limitations
and provisions regarding en route authorizations to use
the global positioning system (GPS) or other RNAV
systems in the NAS. Your POI must ensure that your
long-range navigation program incorporates the
required practices and procedures. These procedures
must be in your manuals and in checklists, as appropriate. Training on the use of long range navigation
equipment and procedures must be included in your
training curriculums, and your minimum equipment
lists (MELs) and maintenance programs must address
the long range navigation equipment. Examples of
other selected areas requiring specialized en route
authorization include the following:
Figure 3-31. High Performance Holding.
3-27
• Class I navigation in the U.S. Class A airspace
using area or long range navigation systems.
• Class II navigation using multiple long range
navigation systems.
• Operations in central East Pacific airspace.
• North Pacific operations.
• Operations within North Atlantic (NAT) minimum navigation performance specifications
(MNPS) airspace.
• Operations in areas of magnetic unreliability.
• North Atlantic operation (NAT/OPS) with two
engine airplanes under Part 121.
• Extended range operations (ER-OPS) with two
engine airplanes under Part 121.
• Special fuel reserves in international operations.
• Planned inflight redispatch or rerelease en route.
• Extended over water operations using a single
long-range communication system.
• Operations in reduced vertical separation minimum (RVSM) airspace.
DIRECT FLIGHTS
There are a number of ways to create shorter routes and
fly off the airways. You can use NACO low and high
altitude en route charts to create routes for direct
flights, although many of the charts do not share the
same scale as the adjacent chart, so a straight line is
virtually impossible to use as a direct route for long
distances. Generally speaking, NACO charts are plotted accurately enough to draw a direct route that can
be flown. A straight line drawn on a NACO en route
chart can be used to determine if a direct route will
avoid airspace such as Class B airspace, restricted
areas, prohibited areas, etc. Because
NACO en route charts use the
Lambert Conformal Conic projection, a straight line is as close as
possible to a geodesic line (better
than a great circle route). The closer
that your route is to the two standard parallels of 33 degrees and 45
degrees on the chart, the better your
straight line. There are cautions,
however. Placing our round earth on
a flat piece of paper causes distortions, particularly on long east-west
routes. If your route is 180 degrees
or 360 degrees, there is virtually no
distortion in the course line.
About the only way you can confidently avoid protected airspace is by the use of some
type of airborne database, including a graphic display
of the airspace on the long-range navigation system
moving map, for example. When not using an airborne
database, leaving a few miles as a buffer helps ensure
that you stay away from protected airspace.
In Figure 3-33 on page 3-28, a straight line on a magnetic course from SCRAN intersection of 270 degrees
direct to the Fort Smith Regional Airport in Arkansas
will pass just north of restricted area R-2401A and B,
and R-2402. Since the airport and the restricted areas
are precisely plotted, there is an assurance that you will
stay north of the restricted areas. From a practical
standpoint, it might be better to fly direct to the Wizer
NDB. This route goes even further north of the
restricted areas and places you over the final approach
fix to Runway 25 at Fort Smith.
One of the most common means for you to fly direct
routes is to use conventional navigation such as VORs.
When flying direct off-airway routes, remember to
apply the FAA distance limitations, based upon
NAVAID service volume.
RANDOM RNAV ROUTES
Random RNAV routes may be an integral solution in
meeting the worldwide demand for increased air traffic system capacity and safety. Random RNAV routes
are direct routes, based on RNAV capability. They are
typically flown between waypoints defined in terms of
latitude and longitude coordinates, degree and distance
fixes, or offsets from established routes and airways at
a specified distance and direction. Radar monitoring by
ATC is required on all random RNAV routes.
With IFR certified RNAV units (GPS or FMS), there are
several questions to be answered, including “Should I
fly airways or should I fly RNAV direct?” One of the
considerations is the determination of the MIA. In most
Note - Only B-747 and DC-10 operations authorized in these areas.
AUTHORIZED AREAS OF
EN ROUTE OPERATION
LIMITATIONS, PROVISIONS,
AND REFERENCE PARAGRAPHS
The 48 contiguous United States
and the District of Columbia
Note 1
Canada, excluding Canadian MNPS
airspace and the areas of magnetic
unreliability as established in the
Canadian AIP
Note SPECIAL REQUIREMENTS:
Note 1 737 Class II navigation operations with a single long-range system
is authorized only within this area of en route operation.
ote au
3
h thorize
- B-7
zed
-73
d o
37 QU
C
UIR
ass
EME EN ME
e
Not ote 3
R
NS
GR
S,
APH
Figure 3-32. Excerpt of Authorized Areas of En Route Operation.
3-28
places in the world at FL 180 and above, the MIA is not
significant since you are well above any terrain or obstacles. On the other hand, a direct route at 18,000 feet from
Salt Lake City, Utah to Denver, Colorado, means terrain
and obstacles are very important. This RNAV direct
route across the Rocky Mountains reduces your distance
by about 17 NM, but radar coverage over the Rockies at
lower altitudes is pretty spotty. This raises numerous
questions. What will air traffic control allow on direct
flights? What will they do if radar coverage is lost? What
altitudes will they allow when they can’t see you on
radar? Do they have altitudes for direct routes? The easy
answer is to file the airways, and then all the airway
MIAs become usable. But with RNAV equipment, a
direct route is more efficient. Even though on some
routes the mileage difference may be negligible, there
are many other cases where the difference in distance is
significant. ATC is required to provide radar separation
on random RNAV routes at FL 450 and below. It is logical to assume that ATC will clear you at an altitude that
allows it to maintain radar contact along the entire route,
which could mean spending additional time and fuel
climbing to an altitude that gives full radar coverage.
All air route traffic control centers have MIAs for their areas
of coverage. Although these altitudes are not published
anywhere, they are available when airborne from ATC.
OFF ROUTE OBSTRUCTION
CLEARANCE ALTITUDE
An off-route obstruction clearance altitude
(OROCA) is an off-route altitude that provides
obstruction clearance with a 1,000-foot buffer in nonmountainous terrain areas and a 2,000-foot buffer in
designated mountainous areas within the U.S. This
altitude may not provide signal coverage from
ground-based navigational aids, air traffic control
radar, or communications coverage. OROCAs are
intended primarily as a pilot tool for emergencies and
situational awareness. OROCAs depicted on NACO
en route charts do not provide you with an acceptable
altitude for terrain and obstruction clearance for the
purposes of off-route, random RNAV direct flights in
either controlled or uncontrolled airspace. OROCAs
are not subject to the same scrutiny as MEAs, MVAs,
MOCAs, and other minimum IFR altitudes. Since
they do not undergo the same obstruction evaluation,
Figure 3-33. Direct Route Navigation.
3-29
airport airspace analysis procedures, or flight inspection, they cannot provide the same level of confidence
as the other minimum IFR altitudes.
If you depart an airport VFR intending to or needing to
obtain an IFR clearance en route, you must be aware of
the position of your aircraft relative to terrain and
obstructions. When accepting a clearance below the
MEA, MIA, MVA, or the OROCA, you are responsible for your own terrain/obstruction clearance until
reaching the MEA, MIA, or MVA. If you are unable
to visually maintain terrain/obstruction clearance, you
should advise the controller and state your intentions.
For all random RNAV flights, there needs to be at least
one waypoint in each ARTCC area through which you
intend to fly. One of the biggest problems in creating
an RNAV direct route is determining if the route goes
through special use airspace. For most direct routes,
the chances of going through prohibited, restricted,
or special use airspace are good. In the U.S., all direct
routes should be planned to avoid prohibited or
restricted airspace by at least 3 NM. If a bend in a
direct route is required to avoid special use airspace,
the turning point needs to be part of the flight plan.
Two of the most prominent long range navigation
systems today include FMS with integrated GPS
and stand-alone GPS. The following example is a
simplified overview showing how the RNAV systems
might be used to fly a random RNAV route:
In Figure 3-35 on page 3-30, you are northeast of
Tuba City VORTAC at FL 200 using RNAV (showing
both GPS and FMS), RNAV direct on a southwesterly
heading to Lindbergh Regional Airport in Winslow.
As you monitor your position and cross check your
avionics against the high altitude en route chart, you
receive a company message instructing you to divert
to Las Vegas, requiring a change in your flight plan as
highlighted on the depicted chart excerpt.
Figure 3-34. Off-Route Obstacle Clearance Altitude.
3-30
During your cockpit review of the high and low altitude
en route charts, you determine that your best course of
action is to fly direct to the MIRAJ waypoint, 28 DME
northeast of the Las Vegas VORTAC on the 045° radial.
This places you 193 NM out on a 259° magnetic course
inbound, and may help you avoid diverting north,
allowing you to bypass the more distant originating
and intermediate fixes feeding into Las Vegas. You
request an RNAV random route clearance direct
MIRAJ to expedite your flight. Denver Center comes
back with the following amended flight plan and initial
clearance into Las Vegas:
Figure 3-35. Random RNAV Route.
3-31
“Marathon five sixty four, turn right heading two six
zero, descend and maintain one six thousand, cleared
present position direct MIRAJ.”
The latitude and longitude coordinates of your present
position on the high altitude chart are N36 19.10, and
W110 40.24 as you change your course. Notice your
GPS moving map (upper left) and the FMS control
display unit (below the GPS), and FMS map mode
navigation displays (to the right of the GPS) as you
reroute your flight to Las Vegas. For situational
awareness, you note that your altitude is well above
any of the OROCAs on your direct route as you arrive
in the Las Vegas area using the low altitude chart.
PUBLISHED RNAV ROUTES
Although RNAV systems allow you to select any number of routes that may or may not be published on a
chart, en route charts are still crucial and required for
RNAV flight. They assist you with both flight planning
and inflight navigation. NACO en route charts are very
helpful in the context of your RNAV flights. Published
RNAV routes are fixed, permanent routes that can be
flight planned and flown by aircraft with RNAV capability. These are being expanded worldwide as new
RNAV routes are developed, and existing charted,
conventional routes are being designated for RNAV
use. It is important to be alert to the rapidly changing
application of RNAV techniques being applied to conventional en route airways. Published RNAV routes may
potentially be found on any NACO en route chart. The
published RNAV route designation may be obvious, or,
on the other hand, RNAV route designations may be
less obvious, as in the case where a published route
shares a common flight track with a conventional airway. Note: Since the use of RNAV is dynamic and
rapidly changing, NACO en route charts are continuously being updated for information changes and you
may find some differences between charts.
According to the International Civil Aviation
Organization (ICAO), who develops standard principles and techniques for international air navigation,
basic designators for air traffic service (ATS) routes
and their use in voice communications have been established in Annex 11. ATS is a generic ICAO term for
flight information service, alerting service, air traffic
advisory service, and air traffic control service. One of
the main purposes of a system of route designators is to
allow both pilots and ATC to make unambiguous reference to RNAV airways and routes. Many countries have
adopted ICAO recommendations with regard to ATS
route designations. Basic designators for ATS routes
consist of a maximum of five, and in no case exceed
six, alpha/numeric characters in order to be usable by
both ground and airborne automation systems. The designator indicates the type of the route such as high/low
altitude, specific airborne navigation equipment
requirements such as RNAV, and the aircraft type using
the route primarily and exclusively. The basic route
designator consists of one or two letter(s) followed by a
number from 1 to 999.
COMPOSITION OF DESIGNATORS
The prefix letters that pertain specifically to RNAV designations are included in the following list:
1. The basic designator consists of one letter of the
alphabet followed by a number from 1 to 999.
The letters may be:
a) A, B, G, R — for routes that form part of
the regional networks of ATS routes and are
not RNAV routes;
b) L, M, N, P — for RNAV routes that form
part of the regional networks of ATS routes;
c) H, J, V, W — for routes that do not form
part of the regional networks of ATS routes
and are not RNAV routes;
d) Q, T, Y, Z — for RNAV routes that do not
form part of the regional networks of ATS
routes.
2. Where applicable, one supplementary letter must
be added as a prefix to the basic designator as
follows:
a) K — to indicate a low level route established for use primarily by helicopters.
b) U — to indicate that the route or portion
thereof is established in the upper airspace;
c) S — to indicate a route established exclusively for use by supersonic airplanes
during acceleration/deceleration and
while in supersonic flight.
3. Where applicable, a supplementary letter may be
added after the basic designator of the ATS route
as a suffix as follows:
a) F — to indicate that on the route or portion
thereof advisory service only is provided;
b) G — to indicate that on the route or portion
thereof flight information service only is
provided;
c) Y — for RNP 1 routes at and above FL 200
to indicate that all turns on the route
between 30° and 90° must be made within
the tolerance of a tangential arc between the
straight leg segments defined with a radius
of 22.5 NM.
3-32
d) Z — for RNP 1 routes at and below FL 190
to indicate that all turns on the route
between 30° and 90° shall be made within
the tolerance of a tangential arc between the
straight leg segments defined with a radius
of 15 NM.
USE OF DESIGNATORS IN COMMUNICATIONS
In voice communications, the basic letter of a designator should be spoken in accordance with the ICAO
spelling alphabet. Where the prefixes K, U or S, specified in 2., above, are used in voice communications,
they should be pronounced as:
K = “Kopter” U = “Upper” S = “Supersonic”
as in the English language.
Where suffixes “F”, “G”, “Y” or “Z” specified in 3.,
above, are used, the flight crew should not be required
to use them in voice communications.
Example:
A11 will be spoken Alfa Eleven
UR5 will be spoken Upper Romeo Five
KB34 will be spoken Kopter Bravo Thirty Four
UW456 F will be spoken Upper Whiskey Four Fifty Six
Figure 3-36 depicts published RNAV routes in the
Gulf of Mexico (black Q100, Q102, and Q105) that
have been added to straighten out the flight segments
and provide an alternative method of navigation to the
LF airway (brown G26), that has since been terminated in this case. The “Q” designation is derived from
the list of basic route designators previously covered,
and correlates with the description for RNAV routes
that do not form part of the regional networks of ATS
routes. Notice the indirect reference to the RNAV
requirement, with the note, “Navigational Equipment
Other than LF or VHF Required.”
Notice in Figure 3-37 that this en route chart
excerpt depicts three published RNAV jet routes,
J804R, J888R, and J996R. The “R” suffix is a supplementary route designator denoting an RNAV
route. The overlapping symbols for the AMOTT
intersection and waypoint indicate that AMOTT
can be identified by conventional navigation or by
latitude and longitude coordinates. Although coordinates were originally included for aircraft equipped
with INS systems, they are now a good way to cross
check between the coordinates on the chart and in the
FMS or GPS databases to ensure you are tracking on
your intended en route course. The AMOTT RNAV
waypoint includes bearing and distance from the
ANCHORAGE VORTAC. In an effort to simplify
the conversion to RNAV, some controlling agencies
Figure 3-36. Published RNAV Routes Replacing LF Airways.
3-33
outside the U.S. have simply designated all conventional routes as RNAV routes at a certain flight
level.
RNAV MINIMUM EN ROUTE ALTITUDE
RNAV MEAs are depicted on some NACO IFR en
route charts, allowing both RNAV and non-RNAV
pilots to use the same chart for instrument navigation.
MINIMUM IFR ALTITUDE
The Minimum IFR altitude (MIA) for operations is
prescribed in Part 91. These MIAs are published on
NACO charts and prescribed in Part 95 for airways and
routes, and in Part 97 for standard instrument approach
procedures. If no applicable minimum altitude is prescribed in Parts 95 or 97, the following MIA applies: In
designated mountainous areas, 2,000 feet above the
highest obstacle within a horizontal distance of 4 NM
from the course to be flown; or other than mountainous
areas, 1,000 feet above the highest obstacle within a
horizontal distance of 4 NM from the course to be
flown; or as otherwise authorized by the Administrator
or assigned by ATC. MIAs are not flight checked for
communication.
Figure 3-37. Published RNAV Jet Routes.
3-34
WAYPOINTS
Waypoints are specified geographical locations, or
fixes, used to define an RNAV route or the flight path
of an aircraft employing RNAV. Waypoints may be any
of the following types: predefined, published waypoints, floating waypoints, or user-defined waypoints.
Predefined, published waypoints are defined relative to
VOR-DME or VORTAC stations or, as with GPS, in
terms of latitude/longitude coordinates.
USER-DEFINED WAYPOINTS
Pilots typically create user-defined waypoints for use
in their own random RNAV direct navigation. They are
newly established, unpublished airspace fixes that are
designated geographic locations/positions that help
provide positive course guidance for navigation and a
means of checking progress on a flight. They may or
may not be actually plotted by the pilot on en route
charts, but would normally be communicated to ATC in
terms of bearing and distance or latitude/longitude. An
example of user-defined waypoints typically includes
those derived from database RNAV systems whereby
latitude/longitude coordinate-based waypoints are gen-
erated by various means including keyboard input, and
even electronic map mode functions used to establish
waypoints with a cursor on the display. Another example
is an offset phantom waypoint, which is a point-in-space
formed by a bearing and distance from NAVAIDs, such as
VORTACs and tactical air navigation (TACAN) stations,
using a variety of navigation systems. When specifying
unpublished waypoints in a flight plan, they can be communicated using the frequency/bearing/distance format or
latitude and longitude, and they automatically become
compulsory reporting points unless otherwise advised by
ATC. All airplanes with latitude and longitude navigation
systems flying above FL 390 must use latitude and
longitude to define turning points.
FLOATING WAYPOINTS
Floating waypoints, or reporting points, represent airspace fixes at a point in space not directly associated
with a conventional airway. In many cases, they may be
established for such purposes as ATC metering fixes,
holding points, RNAV-direct routing, gateway waypoints, STAR origination points leaving the en route
structure, and SID terminating points joining the en
Figure 3-38. Floating Waypoints.
3-35
route structure. In Figure 3-38, in the top example, a
NACO low altitude en route chart depicts three floating
waypoints that have been highlighted, SCORR, FILUP,
and CHOOT. Notice that waypoints are named with
five-letter identifiers that are unique and pronouncable.
Pilots must be careful of similar waypoint names.
Notice on the high altitude en route chart excerpt in the
bottom example, the similar sounding and spelled
floating waypoint named SCOOR, rather than
SCORR. This emphasizes the importance of correctly entering waypoints into database-driven
navigation systems. One waypoint character
incorrectly entered into your navigation system
could adversely affect your flight. The SCOOR
floating reporting point also is depicted on a
Severe Weather Avoidance Plan (SWAP) en route
chart. These waypoints and SWAP routes assist
pilots and controllers when severe weather affects
the East Coast.
COMPUTER NAVIGATION FIXES
An integral part of RNAV using en route charts
typically involves the use of airborne navigation
databases. Database identifiers are depicted on
NACO en route charts enclosed in parentheses, for
example AWIZO waypoint, shown in Figure 3-39.
These identifiers, sometimes referred to as computer
navigation fixes (CNFs), have no ATC function and
should not be used in filing flight plans nor should
they be used when communicating with ATC.
Database identifiers on en route charts are shown
only to enable you to maintain orientation as you use
charts in conjunction with database navigation systems, including RNAV.
Many of the RNAV systems available today make it
all too easy to forget that en route charts are still
required and necessary for flight. As important as
databases are, they really are onboard the airplane to
provide navigation guidance and situational awareness; they are not intended as a substitute for paper
charts. When flying with GPS, FMS, or planning a
flight with a computer, it is important to understand
the limitations of the system you are using, for example, incomplete information, uncodeable procedures,
complex procedures, and database storage limitations.
For more information on databases, refer to Appendix
A, Airborne Navigation Database.
HIGH ALTITUDE AIRSPACE REDESIGN
Historically in the U.S., IFR flights have navigated
along a system of Federal Airways that require pilots to
fly directly toward or away from ground-based navigation aids. RNAV gives users the capability to fly direct
routes between any two points, offering far more flexible and efficient en route operations in the high-altitude
airspace environment. As part of the ongoing National
Airspace Redesign (NAR), the FAA has implemented
the High Altitude Redesign (HAR) program with the
goal of obtaining maximum system efficiency by introducing advanced RNAV routes for suitably equipped
aircraft to use.
Figure 3-39. Computer Navigation Fix.
3-36
Q-ROUTES
Naturally, the routes between some points are very
popular, so these paths are given route designators and
published on charts. The U.S. and Canada use "Q" as
a designator for RNAV routes. Q-Routes 1 through
499 are allocated to the U.S., while Canada is allocated Q-Routes numbered from 500 through 999. The
first Q-Routes were published in 2003. One benefit of
this system is that aircraft with RNAV or RNP capability can fly safely along closely spaced parallel
flight paths on high-density routes, which eases airspace congestion. While the initial overall HAR
implementation will be at FL390 and above, some of
the features may be used at lower altitudes, and some
Q-Routes may be used as low as FL180. A Q-Route is
shown in figure 3-40.
NON-RESTRICTIVE ROUTING
HAR also includes provisions for pilots to choose their
own routes, unconstrained by either conventional airways or Q-Routes. This non-restrictive routing (NRR)
allows pilots of RNAV-equipped aircraft to plan the
most advantageous route for the flight. There are two
ways to designate an NRR route on your flight plan.
One method, point-to-point (PTP), uses the traditional
fixes in the aircraft equipment database and is shown
by placing “PTP” in the first part of the “Remarks”
block of the flight plan. For
aircraft that have the additional waypoints of the
Navigation Reference System
(NRS) in their databases,
“HAR” is placed in the first
part of the “Remarks” block.
NAVIGATION REFERENCE
SYSTEM
The NRS is a grid of waypoints overlying the U.S. that
will be the basis for flight plan
filing and operations in the
redesigned high altitude environment. It will provide
increased flexibility to aircraft
operators and controllers. The
NRS supports flight planning
in a NRR environment and
provides ATC with the ability
to more efficiently manage
tactical route changes for aircraft separation, traffic flow
management, and weather
avoidance. It provides navigation reference waypoints that
pilots can use in requesting
route deviations around
weather areas, which will
improve common understand-
ing between pilots and ATC of the desired flight path.
The NRS will initially include waypoints every 30 minutes of latitude and every two degrees of longitude. In its
final version, the NRS waypoints will have a grid resolution of 1-degree longitude by 10 minutes of latitude. As
database capabilities for the preponderance of aircraft
operating in the high altitude airspace environment
becomes adequate to support more dense NRS resolution, additional NRS waypoints will be established.
T-ROUTES
T-Routes are being created for those who operate at
lower altitudes. T-Routes have characteristics that are
similar to Q-Routes, but they are depicted on low altitude en route charts and are intended for flights below
FL180. The first T-Routes are being pioneered in
Alaska.
IFR TRANSITION ROUTES
In order to expedite the handling of IFR overflight
traffic through Charlotte Approach Control Airspace,
several RNAV routes are published in the
Airport/Facility Directory and available for you when
filing your flight plan. Any RNAV capable aircraft filing flight plan equipment codes of /E, /F, or /G may
file for these routes. Other aircraft may request vectors
along these routes but should only expect vector routes
Figure 3-40. Q-Route
3-37
as workload permits. Altitudes are assigned by ATC
based upon traffic.
IFR transition routes through Class B airspace for general aviation aircraft en route to distant destinations are
highly desirable. Since general aviation aircraft cruise
at altitudes below the ceiling of most Class B airspace
areas, access to that airspace for en route transition
reduces cost and time, and is helpful to pilots in their
flight planning. Establishing RNAV fixes could facilitate the implementation of IFR transition routes,
although every effort should be made to design routes
that can be flown with RNAV or VOR equipment. IFR
transition routes are beneficial even if access is not
available at certain times because of arriving or
departing traffic saturation at
the primary airport. For these
locations, information can be
published to advise pilots when
IFR transition access is not
available.
REQUIRED NAVIGATION
PERFORMANCE
As RNAV systems grow in
sophistication, high technology
FMS and GPS avionics are
gaining popularity as NDBs,
VORs, and LORAN are being
phased out. As a result, new procedures are being introduced,
including RNP, RVSM, and
minimum navigation performance specifications (MNPS).
ICAO defines an RNP “X” specification as requiring on-board
performance monitoring and
alerting. Even such terms as
gross navigation errors
(GNEs) are being introduced
into the navigation equation. If
you commit a GNE in the
North Atlantic oceanic region
of more than 25 NM laterally
or 300 feet vertically, it has a
detrimental effect on the overall targeted level of safety of
the ATC airspace system in
this region. This applies to
commercial operators, as well
as Part 91 operators, all of
whom must be knowledgeable
on procedures for operations
in North Atlantic airspace,
contained in the North Atlantic
MNPS Operations Manual.
RNP types are identified by a single accuracy value.
For example, RNP 1 refers to a required navigation
performance accuracy within 1 NM of the desired
flight path at least 95 percent of the flying time.
Countries around the world are establishing required
navigation performance values. For Federal Airways
in the U.S. that extend 4 NM from either side of the
airway centerline, the airway has an equivalent RNP
of 2. Figure 3-42 on page 3-38 shows ICAO RNP containment parameters, including reference to lateral
and longitudinal total system errors (TSEs).
RNP requires you to learn new procedures, communications, and limitations; and to learn new terminology
that defines and describes navigation concepts. One of
Figure 3-41. IFR Transition Routes in the A po t / Fac yD ec o y .
3-38
these terms is RNP Airspace, a generic term designating airspace, routes, legs, operations, or procedures
where minimum RNP has been established. P-RNAV
represents a 95 percent containment value of ±1 NM.
B-RNAV provides a 95 percent containment value of
±5 NM. RNP is a function of RNAV equipment that
calculates, displays, and provides lateral guidance
to a profile or path. Estimated position error (EPE)
is a measure of your current estimated navigational
performance, also referred to as actual navigation
performance (ANP).
RNP RNAV is an industry-expanded specification
beyond ICAO-defined RNP. Some of the benefits of
RNP RNAV includes being an aid in both separation
and collision risk assessment. RNP RNAV can further
reduce route separation. Figure 3-43 depicts route separation, that can now be reduced to four times the RNP
value, which further increases route capacity within the
same airspace. The containment limit quantifies the
navigation performance where the probability of an
unannunciated deviation greater than 2 x RNP is less
than 1 x 10-
5
. This means that the pilot will be alerted
when the TSE can be greater than the containment
limit. Figure 3-44 shows the U.S. RNP RNAV levels by
airspace control regions, including RNP 2 for the en
route phase of flight, and Figure 3-45 on page 3-40
illustrates the U.S. standard RNP (95%) levels.
REDUCED VERTICAL
SEPARATION MINIMUMS
In 1960, the minimum vertical separation between airplanes
above FL 290 was officially increased to 2,000 feet. This
was necessary because of the relatively large errors in barometric altimeters at high altitudes. Since that time, increased
air traffic worldwide has begun to approach (and sometimes
exceed) the capacity of the most popular high-altitude
routes. Likewise, very accurate altitude determination by
satellite positioning systems makes it possible to change the
minimum vertical separation for properly equipped airplanes back to the pre-1960 standard of 1,000 feet. [Figure
3-46 on page 3-41] RVSM airspace is any airspace between
FL 290 and FL 410 inclusive, where airplanes are separated
by 1,000 feet vertically. In the early 1980’s, programs
were established to study the concept of reduced vertical separation minimums (RVSM). RVSM was found
to be technically feasible without imposing unreasonable requirements on equipment. RVSM is the most
effective way to increase airspace capacity to cope with
traffic growth. Most of the preferred international and
domestic flight routes are under both RVSM and RNP
RNAV rules.
{
{
{
{
Distance to Waypoint
True
Aircraft
Position
Lateral TSE
= RNP Type
Lateral TSE
= RNP Type
Longitudinal TSE
= RNP Type
Longitudinal TSE
= RNP Type
Nav System
Indicated
Position
Desired
Flight Path
Inside the box
95% of Total
Flight Time
Figure 3-42. ICAO RNP Containment Parameters.
3-39
2 X RNP
RNP: 95%
RNP
Containment Limit
Containment Limit: 99.999%
Defined Path
Desired Path
RNP RNAV is referenced to the airplane defined path.
ICAO RNP is referenced to the airspace desired path.
Figure 3-43. RNP RNAV Containment.
U.S. RNP RNAV
LEVELS
ADS-B RNP 1
RNP 2
RNP 0.3
RNP 0.3
Airport Surface
Final Approach/Initial Departure
Approach/Departure Transition
Arrival/Departure
En Route
Figure 3-44. Airspace Control Regions.
3-40
In 1997, the first RVSM 1,000-foot separation was
implemented between FL 330 and FL 370 over the
North Atlantic. In 1998, RVSM was expanded to
include altitudes from FL 310 to FL 390. Today States
(governments) around the globe are implementing
RVSM from FL 290 to FL 410. There are many
requirements for operator approval of RVSM. Each
aircraft must be in compliance with specific RVSM
criteria. A program must be in place to assure continued airworthiness of all RVSM critical systems. Flight
crews, dispatchers, and flight operations must be
properly trained, and operational procedures, checklists, etc. must be established and published in the Ops
Manual and AFM, plus operators must participate in a
height monitoring program.
Using the appropriate suffix in Block 3 on the IFR
flight plan lets ATC know that your flight conforms to
the necessary standards and is capable of using RNP
routes or flying in RVSM airspace. The equipment
codes changed significantly in 2005 and are shown in
Figure 3-47.
Figure 3-45. U.S. Standard RNP Levels.
3-41
FL 330
FL 310
FL 290
FL 280
FL 270
2000 ft
1000 ft
Figure 3-46. Prior to implementation of RVSM, all traffic above FL290 required vertical separation of 2,000 feet.
Figure 3-47. When filed in your IFR flight plan, these codes inform ATC about your aircraft navigation capability.
No DME DME TACAN only Area Navigation (RNAV)
LORAN, VOR/DME, or INS
/D
/B
/A
/M
/N
/P
/Y
/C
/ I
/X
/T
/U
/E
/F
/G
/R
RVSM
/J
/K
/L
/Q
/W
No transponder
Transponder without Mode C
Transponder with Mode C
Advanced RNAV with transponder and Mode C
(If an aircraft is unable to operate with a transponder
and/or Mode C, it will revert to the appropriate code
listed above under Area Navigation.)
With RVSM
3-42
页:
[1]