4-3-23. Use of Aircraft Lights
a. Aircraft position lights are required to be lighted
on aircraft operated on the surface and in flight from
sunset to sunrise. In addition, aircraft equipped with
an anti-collision light system are required to operate
that light system during all types of operations (day
and night). However, during any adverse meteorolog-
ical conditions, the pilot-in-command may
determine that the anti-collision lights should be
turned off when their light output would constitute a
hazard to safety (14 CFR Section 91.209).
Supplementary strobe lights should be turned off on
the ground when they adversely affect ground
personnel or other pilots, and in flight when there are
adverse reflection from clouds.
b. An aircraft anti-collision light system can use
one or more rotating beacons and/or strobe lights, be
colored either red or white, and have different (higher
than minimum) intensities when compared to other
aircraft. Many aircraft have both a rotating beacon
and a strobe light system.
c. The FAA has a voluntary pilot safety program,
Operation Lights On, to enhance the see-and-avoid
concept. Pilots are encouraged to turn on their landing
lights during takeoff; i.e., either after takeoff
clearance has been received or when beginning
takeoff roll. Pilots are further encouraged to turn on
their landing lights when operating below
10,000_feet, day or night, especially when operating
within 10 miles of any airport, or in conditions of
reduced visibility and in areas where flocks of birds
may be expected, i.e.,_coastal areas, lake areas,
around refuse dumps, etc. Although turning on
aircraft lights does enhance the see-and-avoid
concept, pilots should not become complacent about
keeping a sharp lookout for other aircraft. Not all
aircraft are equipped with lights and some pilots may
not have their lights turned on. Aircraft manufactur-
er's recommendations for operation of landing lights
and electrical systems should be observed.
d. Prop and jet blast forces generated by large
aircraft have overturned or damaged several smaller
aircraft taxiing behind them. To avoid similar results,
and in the interest of preventing upsets and injuries to
ground personnel from such forces, the FAA
recommends that air carriers and commercial
operators turn on their rotating beacons anytime their
aircraft engines are in operation. General aviation
pilots using rotating beacon equipped aircraft are also
encouraged to participate in this program which is
designed to alert others to the potential hazard. Since
this is a voluntary program, exercise caution and do
not rely solely on the rotating beacon as an indication
that aircraft engines are in operation.
e. At the discretion of the pilot-in-command turn
on all external illumination, including landing lights,
when taxiing on, across, or holding in position on any
runway. This increases the conspicuity of the aircraft
to controllers and other pilots approaching to land,
taxiing, or crossing the runway. Pilots should comply
with any equipment operating limitations and
consider the effects of landing and strobe lights on
other aircraft in their vicinity. When cleared for
takeoff pilots should turn on any remaining exterior
lights.
AIM 2/14/08
4-3-20 Airport Operations
4-3-24. Flight Inspection/`Flight Check'
Aircraft in Terminal Areas
a. Flight check is a call sign used to alert pilots and
air traffic controllers when a FAA aircraft is engaged
in flight inspection/certification of NAVAIDs and
flight procedures. Flight check aircraft fly preplanned
high/low altitude flight patterns such as grids, orbits,
DME arcs, and tracks, including low passes along the
full length of the runway to verify NAVAID
performance. In most instances, these flight checks
are being automatically recorded and/or flown in an
automated mode.
b. Pilots should be especially watchful and avoid
the flight paths of any aircraft using the call sign
“Flight Check” or “Flight Check Recorded.” The
latter call sign; e.g., “Flight Check 47 Recorded”
indicates that automated flight inspections are in
progress in terminal areas. These flights will
normally receive special handling from ATC. Pilot
patience and cooperation in allowing uninterrupted
recordings can significantly help expedite flight
inspections, minimize costly, repetitive runs, and
reduce the burden on the U.S. taxpayer.
4-3-25. Hand Signals
FIG 4-3-7
Signalman Directs Towing
SIGNALMAN
FIG 4-3-8
Signalman's Position
SIGNALMAN
FIG 4-3-9
All Clear
(O.K.)
AIM 2/14/08
4-3-21
Airport Operations
FIG 4-3-10
Start Engine
POINT
TO
ENGINE
TO BE
STARTED
FIG 4-3-11
Pull Chocks
FIG 4-3-12
Proceed Straight Ahead
FIG 4-3-13
Left Turn
AIM 2/14/08
4-3-22 Airport Operations
FIG 4-3-14
Right Turn
FIG 4-3-15
Slow Down
FIG 4-3-16
Flagman Directs Pilot
FIG 4-3-17
Insert Chocks
AIM 2/14/08
4-3-23
Airport Operations
FIG 4-3-18
Cut Engines
FIG 4-3-19
Night Operation
Use same hand movements
as day operation
FIG 4-3-20
Stop
AIM 2/14/08
4-3-24 Airport Operations
4-3-26. Operations at Uncontrolled
Airports With Automated Surface
Observing System (ASOS)/Automated
Weather Observing System (AWOS)
a. Many airports throughout the National Air-
space System are equipped with either ASOS or
AWOS. At most airports with an operating control
tower or human observer, the weather will be
available to you in an Aviation Routine Weather
Report (METAR) hourly or special observation
format on the Automatic Terminal Information
Service (ATIS) or directly transmitted from the
controller/observer.
b. At uncontrolled airports that are equipped with
ASOS/AWOS with ground-to-air broadcast capabil-
ity, the one-minute updated airport weather should be
available to you within approximately 25 NM of the
airport below 10,000 feet. The frequency for the
weather broadcast will be published on sectional
charts and in the Airport/Facility Directory. Some
part-time towered airports may also broadcast the
automated weather on their ATIS frequency during
the hours that the tower is closed.
c. Controllers issue SVFR or IFR clearances
based_on pilot request, known traffic and reported
weather, i.e., METAR/Nonroutine (Special) Aviation
Weather Report (SPECI) observations, when they are
available. Pilots have access to more current weather
at uncontrolled ASOS/AWOS airports than do the
controllers who may be located several miles away.
Controllers will rely on the pilot to determine the
current airport weather from the ASOS/AWOS. All
aircraft arriving or departing an ASOS/AWOS
equipped uncontrolled airport should monitor the
airport weather frequency to ascertain the status of
the airspace. Pilots in Class E airspace must be alert
for changing weather conditions which may effect the
status of the airspace from IFR/VFR. If ATC service
is required for IFR/SVFR approach/departure or
requested for VFR service, the pilot should advise the
controller that he/she has received the one-minute
weather and state his/her intentions.
EXAMPLE“I have the (airport) one-minute weather, request an ILS
Runway 14 approach.”
REFERENCE-
AIM, Weather Observing Programs, Paragraph 7-1-12.
AIM 2/14/08
4-4-1
ATC Clearances and Aircraft Separation
Section 4. ATC Clearances and Aircraft Separation
4-4-1. Clearance
a. A clearance issued by ATC is predicated on
known traffic and known physical airport conditions.
An ATC clearance means an authorization by ATC,
for the purpose of preventing collision between
known aircraft, for an aircraft to proceed under
specified conditions within controlled airspace. IT IS
NOT AUTHORIZATION FOR A PILOT TO
DEVIATE FROM ANY RULE, REGULATION, OR
MINIMUM ALTITUDE NOR TO CONDUCT
UNSAFE OPERATION OF THE AIRCRAFT.
b. 14 CFR Section 91.3(a) states: “The pilot-in-
command of an aircraft is directly responsible for,
and is the final authority as to, the operation of that
aircraft.” If ATC issues a clearance that would cause
a pilot to deviate from a rule or regulation, or in the
pilot's opinion, would place the aircraft in jeopardy,
IT IS THE PILOT'S RESPONSIBILITY TO
REQUEST AN AMENDED CLEARANCE. Simi-
larly, if a pilot prefers to follow a different course of
action, such as make a 360 degree turn for spacing to
follow traffic when established in a landing or
approach sequence, land on a different runway,
takeoff from a different intersection, takeoff from the
threshold instead of an intersection, or delay
operation, THE PILOT IS EXPECTED TO
INFORM ATC ACCORDINGLY. When the pilot
requests a different course of action, however, the
pilot is expected to cooperate so as to preclude
disruption of traffic flow or creation of conflicting
patterns. The pilot is also expected to use
the_appropriate aircraft call sign to acknowledge all
ATC clearances, frequency changes, or advisory
information.
c. Each pilot who deviates from an ATC clearance
in response to a Traffic Alert and Collision Avoidance
System resolution advisory shall notify ATC of that
deviation as soon as possible.
REFERENCE-
Pilot/Controller Glossary Term- Traffic Alert and Collision Avoidance
System.
d. When weather conditions permit, during the
time an IFR flight is operating, it is the direct
responsibility of the pilot to avoid other aircraft since
VFR flights may be operating in the same area
without the knowledge of ATC. Traffic clearances
provide standard separation only between IFR
flights.
4-4-2. Clearance Prefix
A clearance, control information, or a response to a
request for information originated by an ATC facility
and relayed to the pilot through an air-to-ground
communication station will be prefixed by “ATC
clears,” “ATC advises,” or “ATC requests.”
4-4-3. Clearance Items
ATC clearances normally contain the following:
a. Clearance Limit. The traffic clearance issued
prior to departure will normally authorize flight to the
airport of intended landing. Under certain conditions,
at some locations a short-range clearance procedure
is utilized whereby a clearance is issued to a fix within
or just outside of the terminal area and pilots are
advised of the frequency on which they will receive
the long-range clearance direct from the center
controller.
b. Departure Procedure. Headings to fly and
altitude restrictions may be issued to separate a
departure from other air traffic in the terminal area.
Where the volume of traffic warrants, DPs have been
developed.
REFERENCE-
AIM, Abbreviated IFR Departure Clearance (Cleared. . .as Filed)
Procedures, Paragraph 5-2-4.
AIM, Instrument Departure Procedures (DP) - Obstacle Departure
Procedures (ODP) and Standard Instrument Departures (SID),
Paragraph 5-2-8.
c. Route of Flight.
1. Clearances are normally issued for the
altitude or flight level and route filed by the pilot.
However, due to traffic conditions, it is frequently
necessary for ATC to specify an altitude or flight level
or route different from that requested by the pilot. In
addition, flow patterns have been established in
certain congested areas or between congested areas
whereby traffic capacity is increased by routing all
traffic on preferred routes. Information on these flow
patterns is available in offices where preflight
briefing is furnished or where flight plans are
accepted.
AIM 2/14/08
4-4-2 ATC Clearances and Aircraft Separation
2. When required, air traffic clearances include
data to assist pilots in identifying radio reporting
points. It is the responsibility of pilots to notify ATC
immediately if their radio equipment cannot receive
the type of signals they must utilize to comply with
their clearance.
d. Altitude Data.
1. The altitude or flight level instructions in an
ATC clearance normally require that a pilot
“MAINTAIN” the altitude or flight level at which the
flight will operate when in controlled airspace.
Altitude or flight level changes while en route should
be requested prior to the time the change is desired.
2. When possible, if the altitude assigned is
different from the altitude requested by the pilot, ATC
will inform the pilot when to expect climb or descent
clearance or to request altitude change from another
facility. If this has not been received prior to crossing
the boundary of the ATC facility's area and
assignment at a different altitude is still desired, the
pilot should reinitiate the request with the next
facility.
3. The term “cruise” may be used instead of
“MAINTAIN” to assign a block of airspace to a pilot
from the minimum IFR altitude up to and including
the altitude specified in the cruise clearance. The pilot
may level off at any intermediate altitude within this
block of airspace. Climb/descent within the block is
to be made at the discretion of the pilot. However,
once the pilot starts descent and verbally reports
leaving an altitude in the block, the pilot may not
return to that altitude without additional ATC
clearance.
REFERENCE-
Pilot/Controller Glossary Term- Cruise.
e. Holding Instructions.
1. Whenever an aircraft has been cleared to a fix
other than the destination airport and delay is
expected, it is the responsibility of the ATC controller
to issue complete holding instructions (unless the
pattern is charted), an EFC time, and a best estimate
of any additional en route/terminal delay.
2. If the holding pattern is charted and the
controller doesn't issue complete holding instruc-
tions, the pilot is expected to hold as depicted on the
appropriate chart. When the pattern is charted, the
controller may omit all holding instructions except
the charted holding direction and the statement
AS_PUBLISHED, e.g., “HOLD EAST AS
PUBLISHED.” Controllers shall always issue
complete holding instructions when pilots request
them.
NOTE-
Only those holding patterns depicted on U.S. government
or commercially produced charts which meet FAA
requirements should be used.
3. If no holding pattern is charted and holding
instructions have not been issued, the pilot should ask
ATC for holding instructions prior to reaching the fix.
This procedure will eliminate the possibility of an
aircraft entering a holding pattern other than that
desired by ATC. If unable to obtain holding
instructions prior to reaching the fix (due to
frequency congestion, stuck microphone, etc.), hold
in a standard pattern on the course on which you
approached the fix and request further clearance as
soon as possible. In this event, the altitude/flight level
of the aircraft at the clearance limit will be protected
so that separation will be provided as required.
4. When an aircraft is 3 minutes or less from a
clearance limit and a clearance beyond the fix has not
been received, the pilot is expected to start a speed
reduction so that the aircraft will cross the fix,
initially, at or below the maximum holding airspeed.
5. When no delay is expected, the controller
should issue a clearance beyond the fix as soon as
possible and, whenever possible, at least 5 minutes
before the aircraft reaches the clearance limit.
6. Pilots should report to ATC the time and
altitude/flight level at which the aircraft reaches the
clearance limit and report leaving the clearance limit.
NOTE-
In the event of two-way communications failure, pilots are
required to comply with 14 CFR Section 91.185.
4-4-4. Amended Clearances
a. Amendments to the initial clearance will be
issued at any time an air traffic controller deems such
action necessary to avoid possible confliction
between aircraft. Clearances will require that a flight
“hold” or change altitude prior to reaching the point
where standard separation from other IFR traffic
would no longer exist.
AIM 2/14/08
4-4-3
ATC Clearances and Aircraft Separation
NOTE-
Some pilots have questioned this action and requested
“traffic information” and were at a loss when the reply
indicated “no traffic report.” In such cases the controller
has taken action to prevent a traffic confliction which
would have occurred at a distant point.
b. A pilot may wish an explanation of the handling
of the flight at the time of occurrence; however,
controllers are not able to take time from their
immediate control duties nor can they afford to
overload the ATC communications channels to
furnish explanations. Pilots may obtain an explana-
tion by directing a letter or telephone call to the chief
controller of the facility involved.
c. Pilots have the privilege of requesting a
different clearance from that which has been issued
by ATC if they feel that they have information which
would make another course of action more
practicable or if aircraft equipment limitations or
company procedures forbid compliance with the
clearance issued.
4-4-5. Coded Departure Route (CDR)
a. CDRs provide air traffic control a rapid means
to reroute departing aircraft when the filed route is
constrained by either weather or congestion.
b. CDRs consist of an eight-character designator
that represents a route of flight. The first three
alphanumeric characters represent the departure
airport, characters four through six represent the
arrival airport, and the last two characters are chosen
by the overlying ARTCC. For example, PITORDN1
is an alternate route from Pittsburgh to Chicago.
Participating aircrews may then be re-cleared by air
traffic control via the CDR abbreviated clearance,
PITORDN1.
c. CDRs are updated on the 56 day charting cycle.
Participating aircrews must insure that their CDR is
current.
d. Traditionally, CDRs have been used by air
transport companies that have signed a Memorandum
of Agreement with the local air traffic control facility.
General aviation customers who wish to participate in
the program may now enter “CDR Capable” in the
remarks section of their flight plan.
e. When “CDR Capable” is entered into the
remarks section of the flight plan the general aviation
customer communicates to ATC the ability to decode
the current CDR into a flight plan route and the
willingness to fly a different route than that which
was filed.
4-4-6. Special VFR Clearances
a. An ATC clearance must be obtained prior to
operating within a Class B, Class C, Class D, or
Class_E surface area when the weather is less than that
required for VFR flight. A VFR pilot may request and
be given a clearance to enter, leave, or operate within
most Class_D and Class E surface areas and some
Class B and Class_C surface areas in special VFR
conditions, traffic permitting, and providing such
flight will not delay IFR operations. All special VFR
flights must remain clear of clouds. The visibility
requirements for special VFR aircraft (other than
helicopters) are:
1. At least 1 statute mile flight visibility for
operations within Class B, Class C, Class D, and
Class_E surface areas.
2. At least 1 statute mile ground visibility if
taking off or landing. If ground visibility is not
reported at that airport, the flight visibility must be at
least 1 statute mile.
3. The restrictions in subparagraphs 1 and 2 do
not apply to helicopters. Helicopters must remain
clear of clouds and may operate in Class B, Class C,
Class D, and Class E surface areas with less than
1_statute mile visibility.
b. When a control tower is located within the
Class_B, Class C, or Class D surface area, requests for
clearances should be to the tower. In a Class E surface
area, a clearance may be obtained from the nearest
tower, FSS, or center.
c. It is not necessary to file a complete flight plan
with the request for clearance, but pilots should state
their intentions in sufficient detail to permit ATC to
fit their flight into the traffic flow. The clearance will
not contain a specific altitude as the pilot must remain
clear of clouds. The controller may require the pilot
to fly at or below a certain altitude due to other traffic,
but the altitude specified will permit flight at or above
the minimum safe altitude. In addition, at radar
locations, flights may be vectored if necessary for
control purposes or on pilot request.
NOTE-
The pilot is responsible for obstacle or terrain clearance.
AIM 2/14/08
4-4-4 ATC Clearances and Aircraft Separation
REFERENCE14 CFR Section 91.119, Minimum safe altitudes: General.
d. Special VFR clearances are effective within
Class_B, Class C, Class D, and Class E surface areas
only. ATC does not provide separation after an
aircraft leaves the Class B, Class C, Class D, or
Class_E surface area on a special VFR clearance.
e. Special VFR operations by fixed-wing aircraft
are prohibited in some Class B and Class C surface
areas due to the volume of IFR traffic. A list of these
Class B and Class C surface areas is contained in
14_CFR Part_91, Appendix D, Section 3. They are
also depicted on sectional aeronautical charts.
f. ATC provides separation between Special VFR
flights and between these flights and other IFR
flights.
g. Special VFR operations by fixed-wing aircraft
are prohibited between sunset and sunrise unless the
pilot is instrument rated and the aircraft is equipped
for IFR flight.
h. Pilots arriving or departing an uncontrolled
airport that has automated weather broadcast
capability (ASOS/AWOS) should monitor the
broadcast frequency, advise the controller that they
have the “one-minute weather” and state intentions
prior to operating within the Class B, Class C,
Class_D, or Class E surface areas.
REFERENCE-
Pilot/Controller Glossary Term- One-minute Weather.
4-4-7. Pilot Responsibility upon Clearance
Issuance
a. Record ATC clearance. When conducting an
IFR operation, make a written record of your
clearance. The specified conditions which are a part
of your air traffic clearance may be somewhat
different from those included in your flight plan.
Additionally, ATC may find it necessary to ADD
conditions, such as particular departure route. The
very fact that ATC specifies different or additional
conditions means that other aircraft are involved in
the traffic situation.
b. ATC Clearance/Instruction Readback.
Pilots of airborne aircraft should read back
those_parts of ATC clearances and instructions
containing altitude assignments or vectors as a means
of mutual verification. The readback of the
“numbers” serves as a double check between pilots
and controllers and reduces the kinds of communica-
tions errors that occur when a number is either
“misheard” or is incorrect.
1. Include the aircraft identification in all
readbacks and acknowledgments. This aids control-
lers in determining that the correct aircraft received
the clearance or instruction. The requirement to
include aircraft identification in all readbacks and
acknowledgements becomes more important as
frequency congestion increases and when aircraft
with similar call signs are on the same frequency.
EXAMPLE“Climbing to Flight Level three three zero, United Twelve”
or “November Five Charlie Tango, roger, cleared to land.”
2. Read back altitudes, altitude restrictions, and
vectors in the same sequence as they are given in the
clearance or instruction.
3. Altitudes contained in charted procedures,
such as DPs, instrument approaches, etc., should not
be read back unless they are specifically stated by the
controller.
c. It is the responsibility of the pilot to accept or
refuse the clearance issued.
4-4-8. IFR Clearance VFR-on-top
a. A pilot on an IFR flight plan operating in VFR
weather conditions, may request VFR-on-top in lieu
of an assigned altitude. This permits a pilot to select
an altitude or flight level of their choice (subject to
any ATC restrictions.)
b. Pilots desiring to climb through a cloud, haze,
smoke, or other meteorological formation and then
either cancel their IFR flight plan or operate
VFR-on-top may request a climb to VFR-on-top. The
ATC authorization shall contain either a top report or
a statement that no top report is available, and a
request to report reaching VFR-on-top. Additionally,
the ATC authorization may contain a clearance limit,
routing and an alternative clearance if VFR-on-top is
not reached by a specified altitude.
c. A pilot on an IFR flight plan, operating in VFR
conditions, may request to climb/descend in VFR
conditions.
d. ATC may not authorize VFR-on-top/VFR
conditions operations unless the pilot requests the
VFR operation or a clearance to operate in VFR
conditions will result in noise abatement benefits
AIM 2/14/08
4-4-5
ATC Clearances and Aircraft Separation
where part of the IFR departure route does not
conform to an FAA approved noise abatement route
or altitude.
e. When operating in VFR conditions with an ATC
authorization to “maintain VFR-on-top/maintain
VFR conditions” pilots on IFR flight plans must:
1. Fly at the appropriate VFR altitude as
prescribed in 14 CFR Section 91.159.
2. Comply with the VFR visibility and distance
from cloud criteria in 14 CFR Section 91.155 (Basic
VFR Weather Minimums).
3. Comply with instrument flight rules that are
applicable to this flight; i.e., minimum IFR altitudes,
position reporting, radio communications, course to
be flown, adherence to ATC clearance, etc.
NOTE-
Pilots should advise ATC prior to any altitude change to
insure the exchange of accurate traffic information.
f. ATC authorization to “maintain VFR-on-top” is
not intended to restrict pilots so that they must operate
only above an obscuring meteorological formation
(layer). Instead, it permits operation above, below,
between layers, or in areas where there is no
meteorological obscuration. It is imperative, howev-
er, that pilots understand that clearance to operate
“VFR-on-top/VFR conditions” does not imply
cancellation of the IFR flight plan.
g. Pilots operating VFR-on-top/VFR conditions
may receive traffic information from ATC on other
pertinent IFR or VFR aircraft. However, aircraft
operating in Class B airspace/TRSAs shall be
separated as required by FAA Order JO 7110.65,
Air_Traffic Control.
NOTE-
When operating in VFR weather conditions, it is the pilot's
responsibility to be vigilant so as to see-and-avoid other
aircraft.
h. ATC will not authorize VFR or VFR-on-top
operations in Class A airspace.
REFERENCE-
AIM, Class A Airspace, Paragraph 3-2-2.
4-4-9. VFR/IFR Flights
A pilot departing VFR, either intending to or needing
to obtain an IFR clearance en route, must be aware of
the position of the aircraft and the relative
terrain/obstructions. When accepting a clearance
below the MEA/MIA/MVA/OROCA, pilots are
responsible for their own terrain/obstruction clear-
ance until reaching the MEA/MIA/MVA/OROCA. If
pilots are unable to maintain terrain/obstruction
clearance, the controller should be advised and pilots
should state their intentions.
NOTE-
OROCA is an off-route altitude which provides obstruc-
tion 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.
4-4-10. Adherence to Clearance
a. When air traffic clearance has been obtained
under either visual or instrument flight rules, the
pilot-in-command of the aircraft shall not deviate
from the provisions thereof unless an amended
clearance is obtained. When ATC issues a clearance
or instruction, pilots are expected to execute its
provisions upon receipt. ATC, in certain situations,
will include the word “IMMEDIATELY” in a
clearance or instruction to impress urgency of an
imminent situation and expeditious compliance by
the pilot is expected and necessary for safety. The
addition of a VFR or other restriction; i.e., climb or
descent point or time, crossing altitude, etc., does not
authorize a pilot to deviate from the route of flight or
any other provision of the ATC clearance.
b. When a heading is assigned or a turn is
requested by ATC, pilots are expected to promptly
initiate the turn, to complete the turn, and maintain the
new heading unless issued additional instructions.
c. The term “AT PILOT'S DISCRETION”
included in the altitude information of an ATC
clearance means that ATC has offered the pilot the
option to start climb or descent when the pilot wishes,
is authorized to conduct the climb or descent at any
rate, and to temporarily level off at any intermediate
altitude as desired. However, once the aircraft has
vacated an altitude, it may not return to that altitude.
d. When ATC has not used the term “AT PILOT'S
DISCRETION” nor imposed any climb or descent
restrictions, pilots should initiate climb or descent
promptly on acknowledgement of the clearance.
Descend or climb at an optimum rate consistent with
the operating characteristics of the aircraft to
AIM 2/14/08
4-4-6 ATC Clearances and Aircraft Separation
1,000_feet above or below the assigned altitude, and
then attempt to descend or climb at a rate of between
500 and 1,500 fpm until the assigned altitude is
reached. If at anytime the pilot is unable to climb or
descend 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 or descent, advise ATC, except
when leveling off at 10,000 feet MSL on descent, or
2,500 feet above airport elevation (prior to entering a
Class C or Class D surface area), when required for
speed reduction.
REFERENCE14 CFR Section 91.117.
NOTE-
Leveling off at 10,000 feet MSL on descent or 2,500 feet
above airport elevation (prior to entering a Class_C or
Class D surface area) to comply with 14 CFR
Section_91.117 airspeed restrictions is commonplace.
Controllers anticipate this action and plan accordingly.
Leveling off at any other time on climb or descent may
seriously affect air traffic handling by ATC. Consequently,
it is imperative that pilots make every effort to fulfill the
above expected actions to aid ATC in safely handling and
expediting traffic.
e. If the altitude information of an ATC
DESCENT clearance includes a provision to
“CROSS (fix) AT” or “AT OR ABOVE/BELOW
(altitude),” the manner in which the descent is
executed to comply with the crossing altitude is at the
pilot's discretion. This authorization to descend at
pilot's discretion is only applicable to that portion of
the flight to which the crossing altitude restriction
applies, and the pilot is expected to comply with the
crossing altitude as a provision of the clearance. Any
other clearance in which pilot execution is optional
will so state “AT PILOT'S DISCRETION.”
EXAMPLE1. “United Four Seventeen, descend and maintain
six_thousand.”
NOTE1. The pilot is expected to commence descent upon receipt
of the clearance and to descend at the suggested rates until
reaching the assigned altitude of 6,000 feet.
EXAMPLE2. “United Four Seventeen, descend at pilot's discretion,
maintain six thousand.”
NOTE2. The pilot is authorized to conduct descent within the
context of the term at pilot's discretion as described above.
EXAMPLE3. “United Four Seventeen, cross Lakeview V-O-R at or
above Flight Level two zero zero, descend and maintain
six_thousand.”
NOTE3. The pilot is authorized to conduct descent at pilot's
discretion until reaching Lakeview VOR and must comply
with the clearance provision to cross the Lakeview VOR at
or above FL 200. After passing Lakeview VOR, the pilot is
expected to descend at the suggested rates until reaching
the assigned altitude of 6,000 feet.
EXAMPLE4. “United Four Seventeen, cross Lakeview V-O-R at
six_thousand, maintain six thousand.”
NOTE4. The pilot is authorized to conduct descent at pilot's
discretion, however, must comply with the clearance
provision to cross the Lakeview VOR at 6,000 feet.
EXAMPLE5. “United Four Seventeen, descend now to Flight
Level_two seven zero, cross Lakeview V-O-R at or below
one zero thousand, descend and maintain six thousand.”
NOTE5. The pilot is expected to promptly execute and complete
descent to FL 270 upon receipt of the clearance. After
reaching FL 270 the pilot is authorized to descend “at
pilot's discretion” until reaching Lakeview VOR. The pilot
must comply with the clearance provision to cross
Lakeview VOR at or below 10,000 feet. After Lakeview
VOR the pilot is expected to descend at the suggested rates
until reaching 6,000 feet.
EXAMPLE6. “United Three Ten, descend now and maintain Flight
Level two four zero, pilot's discretion after reaching Flight
Level two eight zero.”
NOTE6. The pilot is expected to commence descent upon receipt
of the clearance and to descend at the suggested rates until
reaching FL 280. At that point, the pilot is authorized to
continue descent to FL 240 within the context of the term
“at pilot's discretion” as described above.
f. In case emergency authority is used to deviate
from provisions of an ATC clearance, the pilot-in-
command shall notify ATC as soon as possible and
obtain an amended clearance. In an emergency
situation which does not result in a deviation from the
rules prescribed in 14 CFR Part 91 but which requires
ATC to give priority to an aircraft, the pilot of such
aircraft shall, when requested by ATC, make a report
within 48 hours of such emergency situation to the
manager of that ATC facility.
AIM 2/14/08
4-4-7
ATC Clearances and Aircraft Separation
g. The guiding principle is that the last ATC
clearance has precedence over the previous ATC
clearance. When the route or altitude in a previously
issued clearance is amended, the controller will
restate applicable altitude restrictions. If altitude to
maintain is changed or restated, whether prior to
departure or while airborne, and previously issued
altitude restrictions are omitted, those altitude
restrictions are canceled, including departure proce-
dures and STAR altitude restrictions.
EXAMPLE1. A departure flight receives a clearance to destination
airport to maintain FL 290. The clearance incorporates a
DP which has certain altitude crossing restrictions. Shortly
after takeoff, the flight receives a new clearance changing
the maintaining FL from 290 to 250. If the altitude
restrictions are still applicable, the controller restates
them.
2. A departing aircraft is cleared to cross Fluky
Intersection at or above 3,000 feet, Gordonville VOR at or
above 12,000 feet, maintain FL 200. Shortly after
departure, the altitude to be maintained is changed to
FL_240. If the altitude restrictions are still applicable, the
controller issues an amended clearance as follows: “cross
Fluky Intersection at or above three thousand, cross
Gordonville V-O-R at or above one two thousand,
maintain Flight Level two four zero.”
3. An arriving aircraft is cleared to the destination airport
via V45 Delta VOR direct; the aircraft is cleared to cross
Delta VOR at 10,000 feet, and then to maintain 6,000 feet.
Prior to Delta VOR, the controller issues an amended
clearance as follows: “turn right heading one eight zero
for vector to runway three six I-L-S approach, maintain
six_thousand.”
NOTE-
Because the altitude restriction “cross Delta V-O-R at
10,000 feet” was omitted from the amended clearance, it is
no longer in effect.
h. Pilots of turbojet aircraft equipped with
afterburner engines should advise ATC prior to
takeoff if they intend to use afterburning during their
climb to the en route altitude. Often, the controller
may be able to plan traffic to accommodate a high
performance climb and allow the aircraft to climb to
the planned altitude without restriction.
i. If an “expedite” climb or descent clearance is
issued by ATC, and the altitude to maintain is
subsequently changed or restated without an expedite
instruction, the expedite instruction is canceled.
Expedite climb/descent normally indicates to the
pilot that the approximate best rate of climb/descent
should be used without requiring an exceptional
change in aircraft handling characteristics. Normally
controllers will inform pilots of the reason for an
instruction to expedite.
4-4-11. IFR Separation Standards
a. ATC effects separation of aircraft vertically by
assigning different altitudes; longitudinally by
providing an interval expressed in time or distance
between aircraft on the same, converging, or crossing
courses, and laterally by assigning different flight
paths.
b. Separation will be provided between all aircraft
operating on IFR flight plans except during that part
of the flight (outside Class B airspace or a TRSA)
being conducted on a VFR-on-top/VFR conditions
clearance. Under these conditions, ATC may issue
traffic advisories, but it is the sole responsibility of the
pilot to be vigilant so as to see and avoid other aircraft.
c. When radar is employed in the separation of
aircraft at the same altitude, a minimum of 3 miles
separation is provided between aircraft operating
within 40 miles of the radar antenna site, and 5 miles
between aircraft operating beyond 40 miles from the
antenna site. These minima may be increased or
decreased in certain specific situations.
NOTE-
Certain separation standards are increased in the terminal
environment when CENRAP is being utilized.
4-4-12. Speed Adjustments
a. ATC will issue speed adjustments to pilots of
radar-controlled aircraft to achieve or maintain
required or desire spacing.
b. ATC will express all speed adjustments in
terms_of knots based on indicated airspeed (IAS) 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 is
restricted to turbojet aircraft with Mach meters.
c. Pilots complying with speed adjustments are
expected to maintain a speed within plus or minus
10_knots or 0.02 Mach number of the specified speed.
d. When ATC assigns speed adjustments, it will
be_in accordance with the following recommended
minimums:
AIM 2/14/08
4-4-8 ATC Clearances and Aircraft Separation
1. To aircraft operating between FL 280 and
10,000 feet, a speed not less than 250 knots or the
equivalent Mach number.
NOTE1. On a standard day the Mach numbers equivalent to
250_knots CAS (subject to minor variations) are:
FL 240-0.6
FL 250-0.61
FL 260-0.62
FL 270-0.64
FL 280-0.65
FL 290-0.66.
2. When an operational advantage will be realized, speeds
lower than the recommended minima may be applied.
2. To arriving turbojet aircraft operating below
10,000 feet:
(a) A speed not less than 210 knots, except;
(b) Within 20 flying miles of the airport of
intended landing, a speed not less than 170 knots.
3. To arriving reciprocating engine or turboprop
aircraft within 20 flying miles of the runway
threshold of the airport of intended landing, a speed
not less than 150 knots.
4. To departing aircraft:
(a) Turbojet aircraft, a speed not less than
230_knots.
(b) Reciprocating engine aircraft, a speed not
less than 150 knots.
e. When ATC combines a speed adjustment with
a descent clearance, the sequence of delivery, with the
word “then” between, indicates the expected order of
execution.
EXAMPLE1. Descend and maintain (altitude); then, reduce speed to
(speed).
2. Reduce speed to (speed); then, descend and maintain
(altitude).
NOTE-
The maximum speeds below 10,000 feet as established in
14 CFR Section 91.117 still apply. If there is any doubt
concerning the manner in which such a clearance is to be
executed, request clarification from ATC.
f. If ATC determines (before an approach
clearance is issued) that it is no longer necessary to
apply speed adjustment procedures, they will inform
the pilot to resume normal speed. Approach
clearances supersede any prior speed adjustment
assignments, and pilots are expected to make their
own speed adjustments, as necessary, to complete the
approach. Under certain circumstances, however, it
may be necessary for ATC to issue further speed
adjustments after approach clearance is issued to
maintain separation between successive arrivals.
Under such circumstances, previously issued speed
adjustments will be restated if that speed is to be
maintained or additional speed adjustments are
requested. ATC must obtain pilot concurrence for
speed adjustments after approach clearances are
issued. Speed adjustments should not be assigned
inside the final approach fix on final or a point 5 miles
from the runway, whichever is closer to the runway.
NOTE-
An instruction to “resume normal speed” does not delete
speed restrictions that are contained in a published
procedure, unless specifically stated by ATC, nor does it
relieve the pilot of those speed restrictions which are
applicable to 14 CFR Section 91.117.
g. The pilots retain the prerogative of rejecting the
application of speed adjustment by ATC if the
minimum safe airspeed for any particular operation is
greater than the speed adjustment.
NOTE-
In such cases, pilots are expected to advise ATC of the
speed that will be used.
h. Pilots are reminded that they are responsible for
rejecting the application of speed adjustment by ATC
if, in their opinion, it will cause them to exceed the
maximum indicated airspeed prescribed by 14 CFR
Section_91.117(a), (c) and (d). IN SUCH CASES,
THE PILOT IS EXPECTED TO SO INFORM ATC.
Pilots operating at or above 10,000 feet MSL who are
issued speed adjustments which exceed 250 knots
IAS and are subsequently cleared below 10,000 feet
MSL are expected to comply with 14 CFR
Section_91.117(a).
i. Speed restrictions of 250 knots do not apply to
U.S. registered aircraft operating beyond 12 nautical
miles from the coastline within the U.S. Flight
Information Region, in Class E airspace below
10,000 feet MSL. However, in airspace underlying a
Class B airspace area designated for an airport, or in
a VFR corridor designated through such as a Class B
airspace area, pilots are expected to comply with the
200 knot speed limit specified in 14 CFR
Section_91.117(c).
AIM 2/14/08
4-4-9
ATC Clearances and Aircraft Separation
j. For operations in a Class C and Class_D surface
area, ATC is authorized to request or approve a speed
greater than the maximum indicated airspeeds
prescribed for operation within that airspace (14 CFR
Section 91.117(b)).
NOTE-
Pilots are expected to comply with the maximum speed of
200 knots when operating beneath Class B airspace or in
a Class B VFR corridor (14 CFR Section 91.117(c)
and_(d)).
k. When in communications with the ARTCC or
approach control facility, pilots should, as a good
operating practice, state any ATC assigned speed
restriction on initial radio contact associated with an
ATC communications frequency change.
4-4-13. Runway Separation
Tower controllers establish the sequence of arriving
and departing aircraft by requiring them to adjust
flight or ground operation as necessary to achieve
proper spacing. They may “HOLD” an aircraft short
of the runway to achieve spacing between it and an
arriving aircraft; the controller may instruct a pilot to
“EXTEND DOWNWIND” in order to establish
spacing from an arriving or departing aircraft. At
times a clearance may include the word “IMMEDI-
ATE.” For example: “CLEARED FOR
IMMEDIATE TAKEOFF.” In such cases “IMMEDI-
ATE” is used for purposes of air traffic separation. It
is up to the pilot to refuse the clearance if, in the pilot's
opinion, compliance would adversely affect the
operation.
REFERENCE-
AIM, Gate Holding due to Departure Delays, Paragraph 4-3-15.
4-4-14. Visual Separation
a. Visual separation is a means employed by ATC
to separate aircraft in terminal areas and en route
airspace in the NAS. There are two methods
employed to effect this separation:
1. The tower controller sees the aircraft
involved and issues instructions, as necessary, to
ensure that the aircraft avoid each other.
2. A pilot sees the other aircraft involved and
upon instructions from the controller provides
separation by maneuvering the aircraft to avoid it.
When pilots accept responsibility to maintain visual
separation, they must maintain constant visual
surveillance and not pass the other aircraft until it is
no longer a factor.
NOTE-
Traffic is no longer a factor when during approach phase
the other aircraft is in the landing phase of flight or
executes a missed approach; and during departure or
en_route, when the other aircraft turns away or is on a
diverging course.
b. A pilot's acceptance of instructions to follow
another aircraft or provide visual separation from it is
an acknowledgment that the pilot will maneuver the
aircraft as necessary to avoid the other aircraft or to
maintain in-trail separation. In operations conducted
behind heavy jet aircraft, it is also an acknowledg-
ment that the pilot accepts the responsibility for wake
turbulence separation.
NOTE-
When a pilot has been told to follow another aircraft or to
provide visual separation from it, the pilot should promptly
notify the controller if visual contact with the other aircraft
is lost or cannot be maintained or if the pilot cannot accept
the responsibility for the separation for any reason.
c. Scanning the sky for other aircraft is a key factor
in collision avoidance. Pilots and copilots (or the right
seat passenger) should continuously scan to cover all
areas of the sky visible from the cockpit. Pilots must
develop an effective scanning technique which
maximizes one's visual capabilities. Spotting a
potential collision threat increases directly as more
time is spent looking outside the aircraft. One must
use timesharing techniques to effectively scan the
surrounding airspace while monitoring instruments
as well.
d. Since the eye can focus only on a narrow
viewing area, effective scanning is accomplished
with a series of short, regularly spaced eye
movements that bring successive areas of the sky into
the central visual field. Each movement should not
exceed ten degrees, and each area should be observed
for at least one second to enable collision detection.
Although many pilots seem to prefer the method of
horizontal back-and-forth scanning every pilot
should develop a scanning pattern that is not only
comfortable but assures optimum effectiveness.
Pilots should remember, however, that they have a
regulatory responsibility (14 CFR Section_91.113(a))
to see and avoid other aircraft when weather
conditions permit.
AIM 2/14/08
4-4-10 ATC Clearances and Aircraft Separation
4-4-15. Use of Visual Clearing Procedures
a. Before Takeoff. Prior to taxiing onto a runway
or landing area in preparation for takeoff, pilots
should scan the approach areas for possible landing
traffic and execute the appropriate clearing maneu-
vers to provide them a clear view of the approach
areas.
b. Climbs and Descents. During climbs and
descents in flight conditions which permit visual
detection of other traffic, pilots should execute gentle
banks, left and right at a frequency which permits
continuous visual scanning of the airspace about
them.
c. Straight and Level. Sustained periods of
straight and level flight in conditions which permit
visual detection of other traffic should be broken at
intervals with appropriate clearing procedures to
provide effective visual scanning.
d. Traffic Pattern. Entries into traffic patterns
while descending create specific collision hazards
and should be avoided.
e. Traffic at VOR Sites. All operators should
emphasize the need for sustained vigilance in the
vicinity of VORs and airway intersections due to the
convergence of traffic.
f. Training Operations. Operators of pilot train-
ing programs are urged to adopt the following
practices:
1. Pilots undergoing flight instruction at all
levels should be requested to verbalize clearing
procedures (call out “clear” left, right, above, or
below) to instill and sustain the habit of vigilance
during maneuvering.
2. High-wing airplane. Momentarily raise the
wing in the direction of the intended turn and look.
3. Low-wing airplane. Momentarily lower the
wing in the direction of the intended turn and look.
4. Appropriate clearing procedures should
precede the execution of all turns including
chandelles, lazy eights, stalls, slow flight, climbs,
straight and level, spins, and other combination
maneuvers.
4-4-16. Traffic Alert and Collision
Avoidance System (TCAS I & II)
a. TCAS I provides proximity warning only, to
assist the pilot in the visual acquisition of intruder
aircraft. No recommended avoidance maneuvers are
provided nor authorized as a direct result of a TCAS_I
warning. It is intended for use by smaller commuter
aircraft holding 10 to 30 passenger seats, and general
aviation aircraft.
b. TCAS II provides traffic advisories (TAs) and
resolution advisories (RAs). Resolution advisories
provide recommended maneuvers in a vertical
direction (climb or descend only) to avoid conflicting
traffic. Airline aircraft, and larger commuter and
business aircraft holding 31 passenger seats or more,
use TCAS II equipment.
1. Each pilot who deviates from an ATC
clearance in response to a TCAS II RA shall notify
ATC of that deviation as soon as practicable and
expeditiously return to the current ATC clearance
when the traffic conflict is resolved.
2. Deviations from rules, policies, or clearances
should be kept to the minimum necessary to satisfy a
TCAS II RA.
3. The serving IFR air traffic facility is not
responsible to provide approved standard IFR
separation to an aircraft after a TCAS II RA maneuver
until one of the following conditions exists:
(a) The aircraft has returned to its assigned
altitude and course.
(b) Alternate ATC instructions have been
issued.
c. TCAS does not alter or diminish the pilot's basic
authority and responsibility to ensure safe flight.
Since TCAS does not respond to aircraft which are
not transponder equipped or aircraft with a
transponder failure, TCAS alone does not ensure safe
separation in every case.
d. At this time, no air traffic service nor handling
is predicated on the availability of TCAS equipment
in the aircraft.
AIM 2/14/08
4-4-11
ATC Clearances and Aircraft Separation
4-4-17. Traffic Information Service (TIS)
a. TIS provides proximity warning only, to assist
the pilot in the visual acquisition of intruder aircraft.
No recommended avoidance maneuvers are provided
nor authorized as a direct result of a TIS intruder
display or TIS alert. It is intended for use by aircraft
in which TCAS is not required.
b. TIS does not alter or diminish the pilot's basic
authority and responsibility to ensure safe flight.
Since TIS does not respond to aircraft which are not
transponder equipped, aircraft with a transponder
failure, or aircraft out of radar coverage, TIS alone
does not ensure safe separation in every case.
c. At this time, no air traffic service nor handling
is predicated on the availability of TIS equipment in
the aircraft.
4-4-18. Automatic Dependent
Surveillance-Broadcast (ADS-B)
a. ADS-B (aircraft-to-aircraft) provides proxim-
ity warning only to assist the pilot in the visual
acquisition of other aircraft. No recommended
avoidance maneuvers are provided nor authorized as
a direct result of an ADS-B display or an ADS-B
alert.
b. ADS-B does not alter or diminish the pilot's
basic authority and responsibility to ensure safe
flight. ADS-B only displays aircraft that are ADS-B
equipped; therefore, aircraft that are not ADS-B
equipped or aircraft that are experiencing an ADS-B
failure will not be displayed. ADS-B alone does not
ensure safe separation.
c. Presently, no air traffic services or handling is
predicated on the availability of an ADS-B cockpit
display. A “traffic-in-sight” reply to ATC must be
based on seeing an aircraft out-the-window, NOT on
the cockpit display.
4-4-19. Traffic Information
Service-Broadcast (TIS-B)
a. TIS-B provides traffic information to assist the
pilot in the visual acquisition of other aircraft. No
recommended avoidance maneuvers are provided
nor authorized as the direct result of a TIS-B display
or TIS-B alert.
b. TIS-B does not alter or diminish the pilot's
basic authority and responsibility to ensure safe
flight. TIS-B only displays aircraft with a function-
ing transponder; therefore, aircraft that are not
transponder equipped, or aircraft that are experienc-
ing a transponder failure, or aircraft out of radar
coverage will not be displayed. TIS-B alone does not
ensure safe separation.
c. Presently, no air traffic services or handling is
predicated on the availability of TIS-B equipment in
aircraft. A “traffic-in-sight” reply to ATC must be
based on seeing an aircraft out-the-window, NOT on
the cockpit display.
AIM 2/14/08
4-5-1
Surveillance Systems
Section 5. Surveillance Systems
4-5-1. Radar
a. Capabilities
1. Radar is a method whereby radio waves are
transmitted into the air and are then received when
they have been reflected by an object in the path of the
beam. Range is determined by measuring the time it
takes (at the speed of light) for the radio wave to go
out to the object and then return to the receiving
antenna. The direction of a detected object from a
radar site is determined by the position of the rotating
antenna when the reflected portion of the radio wave
is received.
2. More reliable maintenance and improved
equipment have reduced radar system failures to a
negligible factor. Most facilities actually have some
components duplicated, one operating and another
which immediately takes over when a malfunction
occurs to the primary component.
b. Limitations
1. It is very important for the aviation
community to recognize the fact that there are
limitations to radar service and that ATC controllers
may not always be able to issue traffic advisories
concerning aircraft which are not under ATC control
and cannot be seen on radar. (See FIG 4-5-1.)
FIG 4-5-1
Limitations to Radar Service
Precipitation Attenuation
The nearby target absorbs and scatters so much of the out-going and returning
energy that the radar does not detect the distant target.
AREA BLACKED OUT
BY ATTENUATION
NOT OBSERVED
OBSERVED
ECHO
(a) The characteristics of radio waves are
such that they normally travel in a continuous straight
line unless they are:
(1) “Bent” by abnormal atmospheric phe-
nomena such as temperature inversions;
(2) Reflected or attenuated by dense
objects such as heavy clouds, precipitation, ground
obstacles, mountains, etc.; or
(3) Screened by high terrain features.
(b) The bending of radar pulses, often called
anomalous propagation or ducting, may cause many
extraneous blips to appear on the radar operator's
display if the beam has been bent toward the ground
or may decrease the detection range if the wave is
bent upward. It is difficult to solve the effects of
anomalous propagation, but using beacon radar and
electronically eliminating stationary and slow
moving targets by a method called moving target
indicator (MTI) usually negate the problem.
(c) Radar energy that strikes dense objects
will be reflected and displayed on the operator's
scope thereby blocking out aircraft at the same range
and greatly weakening or completely eliminating the
display of targets at a greater range. Again, radar
beacon and MTI are very effectively used to combat
ground clutter and weather phenomena, and a method
of circularly polarizing the radar beam will eliminate
some weather returns. A negative characteristic of
MTI is that an aircraft flying a speed that coincides
with the canceling signal of the MTI (tangential or
“blind” speed) may not be displayed to the radar
controller.
(d) Relatively low altitude aircraft will not be
seen if they are screened by mountains or are below
the radar beam due to earth curvature. The only
solution to screening is the installation of strategi-
cally placed multiple radars which has been done in
some areas.
(e) There are several other factors which
affect radar control. The amount of reflective surface
of an aircraft will determine the size of the radar
return. Therefore, a small light airplane or a sleek jet
fighter will be more difficult to see on radar than a
large commercial jet or military bomber. Here again,
the use of radar beacon is invaluable if the aircraft is
AIM 2/14/08
4-5-2 Surveillance Systems
equipped with an airborne transponder. All ARTCCs'
radars in the conterminous U.S. and many airport
surveillance radars have the capability to interrogate
Mode C and display altitude information to the
controller from appropriately equipped aircraft.
However, there are a number of airport surveillance
radars that don't have Mode C display capability and;
therefore, altitude information must be obtained from
the pilot.
(f) At some locations within the ATC en route
environment, secondary-radar-only (no primary
radar) gap filler radar systems are used to give lower
altitude radar coverage between two larger radar
systems, each of which provides both primary and
secondary radar coverage. In those geographical
areas served by secondary-radar only, aircraft
without transponders cannot be provided with radar
service. Additionally, transponder equipped aircraft
cannot be provided with radar advisories concerning
primary targets and weather.
REFERENCE-
Pilot/Controller Glossary Term- Radar.
(g) The controller's ability to advise a pilot
flying on instruments or in visual conditions of the
aircraft's proximity to another aircraft will be limited
if the unknown aircraft is not observed on radar, if no
flight plan information is available, or if the volume
of traffic and workload prevent issuing traffic
information. The controller's first priority is given to
establishing vertical, lateral, or longitudinal separa-
tion between aircraft flying IFR under the control of
ATC.
c. FAA radar units operate continuously at the
locations shown in the Airport/Facility Directory, and
their services are available to all pilots, both civil and
military. Contact the associated FAA control tower or
ARTCC on any frequency guarded for initial
instructions, or in an emergency, any FAA facility for
information on the nearest radar service.
4-5-2. Air Traffic Control Radar Beacon
System (ATCRBS)
a. The ATCRBS, sometimes referred to as
secondary surveillance radar, consists of three main
components:
1. Interrogator. Primary radar relies on a
signal being transmitted from the radar antenna site
and for this signal to be reflected or “bounced back”
from an object (such as an aircraft). This reflected
signal is then displayed as a “target” on the
controller's radarscope. In the ATCRBS, the
Interrogator, a ground based radar beacon transmit-
ter-receiver, scans in synchronism with the primary
radar and transmits discrete radio signals which
repetitiously request all transponders, on the mode
being used, to reply. The replies received are then
mixed with the primary returns and both are
displayed on the same radarscope.
2. Transponder. This airborne radar beacon
transmitter-receiver automatically receives the sig-
nals from the interrogator and selectively replies with
a specific pulse group (code) only to those
interrogations being received on the mode to which
it is set. These replies are independent of, and much
stronger than a primary radar return.
3. Radarscope. The radarscope used by the
controller displays returns from both the primary
radar system and the ATCRBS. These returns, called
targets, are what the controller refers to in the control
and separation of traffic.
b. The job of identifying and maintaining
identification of primary radar targets is a long and
tedious task for the controller. Some of the
advantages of ATCRBS over primary radar are:
1. Reinforcement of radar targets.
2. Rapid target identification.
3. Unique display of selected codes.
c. A part of the ATCRBS ground equipment is the
decoder. This equipment enables a controller to
assign discrete transponder codes to each aircraft
under his/her control. Normally only one code will be
assigned for the entire flight. Assignments are made
by the ARTCC computer on the basis of the National
Beacon Code Allocation Plan. The equipment is also
designed to receive Mode C altitude information
from the aircraft.
NOTE-
Refer to figures with explanatory legends for an illustration
of the target symbology depicted on radar scopes in the
NAS Stage A (en route), the ARTS III (terminal) Systems,
and other nonautomated (broadband) radar systems. (See
FIG 4-5-2 and FIG 4-5-3.)
d. It should be emphasized that aircraft transpond-
ers greatly improve the effectiveness of radar
systems.
REFERENCE-
AIM, Transponder Operation, Paragraph 4-1-19.
AIM 2/14/08
4-5-3
Surveillance Systems
FIG 4-5-2
ARTS III Radar Scope With Alphanumeric Data
NOTE-
A number of radar terminals do not have ARTS equipment. Those facilities and certain ARTCCs outside the contiguous U.S.
would have radar displays similar to the lower right hand subset. ARTS facilities and NAS Stage A ARTCCs, when operating
in the nonautomation mode, would also have similar displays and certain services based on automation may not be
available.
AIM 2/14/08
4-5-4 Surveillance Systems
EXAMPLE-
1. Areas of precipitation (can be reduced by CP)
2. Arrival/departure tabular list
3. Trackball (control) position symbol (A)
4. Airway (lines are sometimes deleted in part)
5. Radar limit line for control
6. Obstruction (video map)
7. Primary radar returns of obstacles or terrain (can be
removed by MTI)
8. Satellite airports
9. Runway centerlines (marks and spaces indicate
miles)
10. Primary airport with parallel runways
11. Approach gates
12. Tracked target (primary and beacon target)
13. Control position symbol
14. Untracked target select code (monitored) with
Mode_C readout of 5,000'
15. Untracked target without Mode C
16. Primary target
17. Beacon target only (secondary radar) (transponder)
18. Primary and beacon target
19. Leader line
20. Altitude Mode C readout is 6,000'
(Note: readouts may not be displayed because of
nonreceipt of beacon information, garbled beacon
signals, and flight plan data which is displayed
alternately with the altitude readout)
21. Ground speed readout is 240 knots
(Note: readouts may not be displayed because of a loss
of beacon signal, a controller alert that a pilot was
squawking emergency, radio failure, etc.)
22. Aircraft ID
23. Asterisk indicates a controller entry in Mode C
block. In this case 5,000' is entered and “05” would
alternate with Mode C readout.
24. Indicates heavy
25. “Low ALT” flashes to indicate when an aircraft's
predicted descent places the aircraft in an unsafe
proximity to terrain.
(Note: this feature does not function if the aircraft is not
squawking Mode C. When a helicopter or aircraft is
known to be operating below the lower safe limit, the
“low ALT” can be changed to “inhibit” and flashing
ceases.)
26. NAVAIDs
27. Airways
28. Primary target only
29. Nonmonitored. No Mode C (an asterisk would
indicate nonmonitored with Mode C)
30. Beacon target only (secondary radar based on
aircraft transponder)
31. Tracked target (primary and beacon target) control
position A
32. Aircraft is squawking emergency Code 7700 and is
nonmonitored, untracked, Mode C
33. Controller assigned runway 36 right alternates with
Mode C readout
(Note: a three letter identifier could also indicate the
arrival is at specific airport)
34. Ident flashes
35. Identing target blossoms
36. Untracked target identing on a selected code
37. Range marks (10 and 15 miles) (can be
changed/offset)
38. Aircraft controlled by center
39. Targets in suspend status
40. Coast/suspend list (aircraft holding, temporary loss
of beacon/target, etc.)
41. Radio failure (emergency information)
42. Select beacon codes (being monitored)
43. General information (ATIS, runway, approach in
use)
44. Altimeter setting
45. Time
46. System data area
AIM 2/14/08
4-5-5
Surveillance Systems
FIG 4-5-3
NAS Stage A Controllers View Plan Display
This figure illustrates the controller's radar scope (PVD) when operating in the full automation (RDP) mode, which is
normally 20 hours per day.
(When not in automation mode, the display is similar to the broadband mode shown in the ARTS III radar scope figure.
Certain ARTCCs outside the contiguous U.S. also operate in “broadband” mode.)
25
26
X
X
X
X
X
X
X
X
X
#
X
X
X
280C
33
AAL373
191H-095
VIG123
310N
170 143
NWA258
AAL353
231
70 2734
R15909
170C
290
2103
140 + 143
460
N1467F
UAL33
100A
296
7700
EMRG
7600
RDOF
1200
85
1200
+ + +
+ UAL712
310N
228CST
1
22 23
24
27
28
29
29
30
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
H
H
H
H
H
H
H
H
H H
H
H
H
RADAR SERVICES AND PROCEDURES
AIM 2/14/08
4-5-6 Surveillance Systems
EXAMPLE-
Target symbols:
1. Uncorrelated primary radar target [+]
2. Correlated primary radar target
_See note below.
3. Uncorrelated beacon target [ / ]
4. Correlated beacon target [ \ ]
5. Identing beacon target
_Note: in Number 2 correlated means the association of
radar data with the computer projected track of an
identified aircraft.
Position symbols:
6. Free track (no flight plan tracking)
7. Flat track (flight plan tracking) [◊]
8. Coast (beacon target lost) [#]
9. Present position hold [ _ ]
Data block information:
10. Aircraft ident
_See note below.
11. Assigned altitude FL 280, Mode C altitude same or
within _ 200' of assigned altitude.
_See note below.
12. Computer ID #191, handoff is to sector 33
(0-33 would mean handoff accepted)
_See note below.
13. Assigned altitude 17,000', aircraft is climbing,
Mode_C readout was 14,300 when last beacon interroga-
tion was received.
14. Leader line connecting target symbol and data block
15. Track velocity and direction vector line (projected
ahead of target)
16. Assigned altitude 7,000, aircraft is descending, last
Mode C readout (or last reported altitude) was 100' above
FL 230
17. Transponder code shows in full data block only when
different than assigned code
18. Aircraft is 300' above assigned altitude
19. Reported altitude (no Mode C readout) same as
assigned. (An “n” would indicate no reported altitude.)
20. Transponder set on emergency Code 7700 (EMRG
flashes to attract attention)
21. Transponder Code 1200 (VFR) with no Mode C
22. Code 1200 (VFR) with Mode C and last altitude
readout
23. Transponder set on radio failure Code 7600 (RDOF
flashes)
24. Computer ID #228, CST indicates target is in coast
status
25. Assigned altitude FL 290, transponder code (these two
items constitute a “limited data block”)
_Note: numbers 10, 11, and 12 constitute a “full data
block”
Other symbols:
26. Navigational aid
27. Airway or jet route
28. Outline of weather returns based on primary radar.
“H” represents areas of high density precipitation which
might be thunderstorms. Radial lines indicated lower
density precipitation.
29. Obstruction
30. Airports
Major:
Small:
AIM 2/14/08
4-5-7
Surveillance Systems
4-5-3. Surveillance Radar
a. Surveillance radars are divided into two general
categories: Airport Surveillance Radar (ASR) and
Air Route Surveillance Radar (ARSR).
1. ASR is designed to provide relatively
short-range coverage in the general vicinity of an
airport and to serve as an expeditious means of
handling terminal area traffic through observation of
precise aircraft locations on a radarscope. The ASR
can also be used as an instrument approach aid.
2. ARSR is a long-range radar system designed
primarily to provide a display of aircraft locations
over large areas.
3. Center Radar Automated Radar Terminal
Systems (ARTS) Processing (CENRAP) was devel-
oped to provide an alternative to a nonradar
environment at terminal facilities should an ASR fail
or malfunction. CENRAP sends aircraft radar beacon
target information to the ASR terminal facility
equipped with ARTS. Procedures used for the
separation of aircraft may increase under certain
conditions when a facility is utilizing CENRAP
because radar target information updates at a slower
rate than the normal ASR radar. Radar services for
VFR aircraft are also limited during CENRAP
operations because of the additional workload
required to provide services to IFR aircraft.
b. Surveillance radars scan through 360 degrees of
azimuth and present target information on a radar
display located in a tower or center. This information
is used independently or in conjunction with other
navigational aids in the control of air traffic.
4-5-4. Precision Approach Radar (PAR)
a. PAR is designed for use as a landing aid rather
than an aid for sequencing and spacing aircraft. PAR
equipment may be used as a primary landing aid (See
Chapter 5, Air Traffic Procedures, for additional
information), or it may be used to monitor other types
of approaches. It is designed to display range,
azimuth, and elevation information.
b. Two antennas are used in the PAR array, one
scanning a vertical plane, and the other scanning
horizontally. Since the range is limited to 10 miles,
azimuth to 20 degrees, and elevation to 7 degrees,
only the final approach area is covered. Each scope is
divided into two parts. The upper half presents
altitude and distance information, and the lower half
presents azimuth and distance.
4-5-5. Airport Surface Detection
Equipment - Model X (ASDE-X)
a. The Airport Surface Detection Equipment_-
Model X (ASDE-X) is a multi-sensor surface
surveillance system the FAA is acquiring for airports
in the United States. This system will provide high
resolution, short-range, clutter free surveillance
information about aircraft and vehicles, both moving
and fixed, located on or near the surface of the
airport's runways and taxiways under all weather and
visibility conditions. The system consists of:
1. A Primary Radar System. ASDE-X sys-
tem coverage includes the airport surface and the
airspace up to 200 feet above the surface. Typically
located on the control tower or other strategic
location on the airport, the Primary Radar antenna is
able to detect and display aircraft that are not
equipped with or have malfunctioning transponders.
2. Interfaces. ASDE-X contains an automa-
tion interface for flight identification via all
automation platforms and interfaces with the
terminal radar for position information.
3. ASDE-X Automation. A Multi-sensor
Data Processor (MSDP) combines all sensor reports
into a single target which is displayed to the air traffic
controller.
4. Air Traffic Control Tower Display. A high
resolution, color monitor in the control tower cab
provides controllers with a seamless picture of airport
operations on the airport surface.
b. The combination of data collected from the
multiple sensors ensures that the most accurate
information about aircraft location is received in the
tower, thereby increasing surface safety and
efficiency.
AIM 2/14/08
4-5-8 Surveillance Systems
c. The following facilities have been projected to
receive ASDE-X:
TBL 4-5-1
STL Lambert-St. Louis International
CLT Charlotte Douglas International
SDF Louisville International Standiford
DFW Dallas/Ft. Worth International
ORD Chicago O'Hare International
LAX Los Angeles International
ATL Hartsfield Atlanta International
IAD Washington Dulles International
SEA Seattle-Tacoma International
MKE General Mitchell International
MCO Orlando International
PVD Theodore Francis Green State
PHX Phoenix Sky Harbor International
MEM Memphis International
RDU Raleigh-Durham International
HOU William P. Hobby (Houston, TX)
BDL Bradley International
SJC San Jose International
SAT San Antonio International
SMF Sacramento International
FLL Ft. Lauderdale/Hollywood
HNL Honolulu International - Hickam AFB
OAK Metropolitan Oakland International
IND Indianapolis International
TPA Tampa International
BUR Burbank-Glendale-Pasadena
CMH Port Columbus International
MDW Chicago Midway
COS Colorado Springs Municipal
SNA John Wayne - Orange County
ONT Ontario International
AUS Austin-Bergstrom International
RNO Reno/Tahoe International
ABQ Albuquerque International Sunport
SJU San Juan International
NOTE-
The installation of ASDE-X is projected to be completed by
2009.
4-5-6. Traffic Information Service (TIS)
a. Introduction
The Traffic Information Service (TIS) provides
information to the cockpit via data link, that is similar
to VFR radar traffic advisories normally received
over voice radio. Among the first FAA-provided data
services, TIS is intended to improve the safety and
efficiency of “see and avoid” flight through an
automatic display that informs the pilot of nearby
traffic and potential conflict situations. This traffic
display is intended to assist the pilot in visual
acquisition of these aircraft. TIS employs an
enhanced capability of the terminal Mode S radar
system, which contains the surveillance data, as well
as the data link required to “uplink” this information
to suitably-equipped aircraft (known as a TIS
“client”). TIS provides estimated position, altitude,
altitude trend, and ground track information for up to
8 intruder aircraft within 7 NM horizontally,
+3,500_and -3,000 feet vertically of the client aircraft
(see FIG 4-5-4, TIS Proximity Coverage Volume).
The range of a target reported at a distance greater
than 7_NM only indicates that this target will be a
threat within 34 seconds and does not display an
precise distance. TIS will alert the pilot to aircraft
(under surveillance of the Mode S radar) that are
estimated to be within 34 seconds of potential
collision, regardless of distance of altitude. TIS
surveillance data is derived from the same radar used
by ATC; this data is uplinked to the client aircraft on
each radar scan (nominally every 5 seconds).
b. Requirements
1. In order to use TIS, the client and any intruder
aircraft must be equipped with the appropriate
cockpit equipment and fly within the radar coverage
of a Mode S radar capable of providing TIS.
Typically, this will be within 55 NM of the sites
depicted in FIG 4-5-5, Terminal Mode S Radar Sites.
ATC communication is not a requirement to receive
TIS, although it may be required by the particular
airspace or flight operations in which TIS is being
used.
AIM 2/14/08
4-5-9
Surveillance Systems
FIG 4-5-4
TIS Proximity Coverage Volume
FIG 4-5-5
Terminal Mode S Radar Sites
AIM 2/14/08
4-5-10 Surveillance Systems
FIG 4-5-6
Traffic Information Service (TIS)
Avionics Block Diagram
AIM 2/14/08
4-5-11
Surveillance Systems
2. The cockpit equipment functionality required
by a TIS client aircraft to receive the service consists
of the following (refer to FIG 4-5-6):
(a) Mode S data link transponder with
altitude encoder.
(b) Data link applications processor with TIS
software installed.
(c) Control-display unit.
(d) Optional equipment includes a digital
heading source to correct display errors caused by
“crab angle” and turning maneuvers.
NOTE-
Some of the above functions will likely be combined into
single pieces of avionics, such as (a) and (b).
3. To be visible to the TIS client, the intruder
aircraft must, at a minimum, have an operating
transponder (Mode A, C or S). All altitude
information provided by TIS from intruder aircraft is
derived from Mode C reports, if appropriately
equipped.
4. TIS will initially be provided by the terminal
Mode S systems that are paired with ASR-9 digital
primary radars. These systems are in locations with
the greatest traffic densities, thus will provide the
greatest initial benefit. The remaining terminal
Mode_S sensors, which are paired with ASR-7 or
ASR-8 analog primary radars, will provide TIS
pending modification or relocation of these sites. See
FIG 4-5-5, Terminal Mode S Radar Sites, for site
locations. There is no mechanism in place, such as
NOTAMs, to provide status update on individual
radar sites since TIS is a nonessential, supplemental
information service.
The FAA also operates en route Mode S radars (not
illustrated) that rotate once every 12 seconds. These
sites will require additional development of TIS
before any possible implementation. There are no
plans to implement TIS in the en route Mode S radars
at the present time.
c. Capabilities
1. TIS provides ground-based surveillance
information over the Mode S data link to properly
equipped client aircraft to aid in visual acquisition of
proximate air traffic. The actual avionics capability of
each installation will vary and the supplemental
handbook material must be consulted prior to using
TIS. A maximum of eight (8) intruder aircraft may be
displayed; if more than eight aircraft match intruder
parameters, the eight “most significant” intruders are
uplinked. These “most significant” intruders are
usually the ones in closest proximity and/or the
greatest threat to the TIS client.
2. TIS, through the Mode S ground sensor,
provides the following data on each intruder aircraft:
(a) Relative bearing information in 6-degree
increments.
(b) Relative range information in 1/8 NM to
1 NM increments (depending on range).
(c) Relative altitude in 100-foot increments
(within 1,000 feet) or 500-foot increments (from
1,000-3,500 feet) if the intruder aircraft has operating
altitude reporting capability.
(d) Estimated intruder ground track in
45-degree increments.
(e) Altitude trend data (level within 500 fpm
or climbing/descending >500 fpm) if the intruder
aircraft has operating altitude reporting capability.
(f) Intruder priority as either an “traffic
advisory” or “proximate” intruder.
3. When flying from surveillance coverage of
one Mode S sensor to another, the transfer of TIS is
an automatic function of the avionics system and
requires no action from the pilot.
4. There are a variety of status messages that are
provided by either the airborne system or ground
equipment to alert the pilot of high priority intruders
and data link system status. These messages include
the following:
(a) Alert. Identifies a potential collision
hazard within 34 seconds. This alert may be visual
and/or audible, such as a flashing display symbol or
a headset tone. A target is a threat if the time to the
closest approach in vertical and horizontal coordi-
nates is less than 30 seconds and the closest approach
is expected to be within 500 feet vertically and
0.5_nautical miles laterally.
(b) TIS Traffic. TIS traffic data is displayed.
(c) Coasting. The TIS display is more than
6_seconds old. This indicates a missing uplink from
the ground system. When the TIS display information
is more than 12 seconds old, the “No Traffic” status
will be indicated.
AIM 2/14/08
4-5-12 Surveillance Systems
(d) No Traffic. No intruders meet proximate
or alert criteria. This condition may exist when the
TIS system is fully functional or may indicate
“coasting” between 12 and 59 seconds old (see (c)
above).
(e) TIS Unavailable. The pilot has re-
quested TIS, but no ground system is available. This
condition will also be displayed when TIS uplinks are
missing for 60 seconds or more.
(f) TIS Disabled. The pilot has not requested
TIS or has disconnected from TIS.
(g) Good-bye. The client aircraft has flown
outside of TIS coverage.
NOTE-
Depending on the avionics manufacturer implementation,
it is possible that some of these messages will not be directly
available to the pilot.
5. Depending on avionics system design, TIS
may be presented to the pilot in a variety of different
displays, including text and/or graphics. Voice
annunciation may also be used, either alone or in
combination with a visual display. FIG 4-5-6,
Traffic Information Service (TIS), Avionics Block
Diagram, shows an example of a TIS display using
symbology similar to the Traffic Alert and Collision
Avoidance System (TCAS) installed on most
passenger air carrier/commuter aircraft in the U.S.
The small symbol in the center represents the client
aircraft and the display is oriented “track up,” with the
12 o'clock position at the top. The range rings
indicate 2 and 5_NM. Each intruder is depicted by a
symbol positioned at the approximate relative
bearing and range from the client aircraft. The
circular symbol near the center indicates an “alert”
intruder and the diamond symbols indicate “proxi-
mate” intruders.
6. The inset in the lower right corner of
FIG 4-5-6, Traffic Information Service (TIS),
Avionics Block Diagram, shows a possible TIS data
block display. The following information is con-
tained in this data block:
(a) The intruder, located approximately
four_o'clock, three miles, is a “proximate” aircraft
and currently not a collision threat to the client
aircraft. This is indicated by the diamond symbol
used in this example.
(b) The intruder ground track diverges to the
right of the client aircraft, indicated by the small
arrow.
(c) The intruder altitude is 700 feet less than
or below the client aircraft, indicated by the “-07”
located under the symbol.
(d) The intruder is descending >500 fpm,
indicated by the downward arrow next to the “-07”
relative altitude information. The absence of this
arrow when an altitude tag is present indicates level
flight or a climb/descent rate less than 500 fpm.
NOTE-
If the intruder did not have an operating altitude encoder
(Mode C), the altitude and altitude trend “tags” would
have been omitted.
d. Limitations
1. TIS is NOT intended to be used as a collision
avoidance system and does not relieve the pilot
responsibility to “see and avoid” other aircraft (see
paragraph 5-5-8, See and Avoid). TIS shall not be for
avoidance maneuvers during IMC or other times
when there is no visual contact with the intruder
aircraft. TIS is intended only to assist in visual
acquisition of other aircraft in VMC. No recom-
mended avoidance maneuvers are provided for,
nor authorized, as a direct result of a TIS intruder
display or TIS alert.
2. While TIS is a useful aid to visual traffic
avoidance, it has some system limitations that must
be fully understood to ensure proper use. Many of
these limitations are inherent in secondary radar
surveillance. In other words, the information
provided by TIS will be no better than that provided
to ATC. Other limitations and anomalies are
associated with the TIS predictive algorithm.
(a) Intruder Display Limitations. TIS will
only display aircraft with operating transponders
installed. TIS relies on surveillance of the Mode S
radar, which is a “secondary surveillance” radar
similar to the ATCRBS described in para-
graph_4-5-2.
(b) TIS Client Altitude Reporting Require-
ment. Altitude reporting is required by the TIS client
aircraft in order to receive TIS. If the altitude encoder
is inoperative or disabled, TIS will be unavailable, as
TIS requests will not be honored by the ground
system. As such, TIS requires altitude reporting to
determine the Proximity Coverage Volume as
AIM 2/14/08
4-5-13
Surveillance Systems
indicated in FIG 4-5-4. TIS users must be alert to
altitude encoder malfunctions, as TIS has no
mechanism to determine if client altitude reporting is
correct. A failure of this nature will cause erroneous
and possibly unpredictable TIS operation. If this
malfunction is suspected, confirmation of altitude
reporting with ATC is suggested.
