CAUTION-
Unless your aircraft’s ILS equipment includes reverse
sensing capability, when flying inbound on the back
course it is necessary to steer the aircraft in the direction
AIP ENR 4.1-5
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
opposite of the needle deflection on the airborne
equipment when making corrections from off-course to
on-course. This _flying away from the needle" is also
required when flying outbound on the front course of the
localizer. Do not use back course signals for approach
unless a back course approach procedure is published for
that particular runway and the approach is authorized by
ATC.
7.2.4_Identification is in Morse Code and consists of
a three-letter identifier preceded by the letter I ( )
transmitted on the localizer frequency.
EXAMPLE-
I-DIA
7.2.5_The localizer provides course guidance
throughout the descent path to the runway threshold
from a distance of 18 NM from the antenna between
an altitude of 1,000 feet above the highest terrain
along the course line and 4,500 feet above the
elevation of the antenna site. Proper off-course
indications are provided throughout the following
angular areas of the operational service volume:
7.2.5.1_To 10_ either side of the course along a radius
of 18 NM from the antenna.
7.2.5.2_From 10_ to 35_either side of the course
along a radius of 10 NM. (See FIG ENR 4.1-1.)
7.2.6_Unreliable signals may be received outside
these areas.
FIG ENR 4.1-1
Limits of Localizer Coverage
7.3_Localizer-Type Directional Aid
7.3.1_The localizer-type directional aid (LDA) is of
comparable use and accuracy to a localizer but is not
part of a complete ILS. The LDA course usually
provides a more precise approach course than the
similar Simplified Directional Facility (SDF) instal-
lation, which may have a course width of 6 degrees or
12 degrees.
7.3.2_The LDA is not aligned with the runway.
Straight-in minimums may be published where
alignment does not exceed 30 degrees between the
course and runway. Circling minimums only are
published where this alignment exceeds 30 degrees._
7.3.3_A very limited number of LDA approaches
also incorporate a glideslope. These are annotated in
the plan view of the instrument approach chart with
a note, _LDA/Glideslope." These procedures fall
under a newly defined category of approaches called
Approach with Vertical Guidance (APV) described in
Section ENR 1.5, paragraph 12, Instrument Approach Procedure Charts, subparagraph 12.1.7.2,
Approach with Vertical Guidance (APV). LDA
minima for with and without glideslope is provided
and annotated on the minima lines of the approach
chart as S-LDA/GS and S-LDA. Because the final
approach course is not aligned with the runway
centerline, additional maneuvering will be required
compared to an ILS approach.
7.4_Glide Slope/Glide Path
7.4.1_The UHF glide slope transmitter, operating on
one of the 40 ILS channels within the frequency range
329.15 MHz, to 335.00 MHz radiates its signals in the
direction of the localizer front course.
CAUTION-
False glide slope signals may exist in the area of the
localizer back course approach which can cause the glide
slope flag alarm to disappear and present unreliable glide
slope information. Disregard all glide slope signal
indications when making a localizer back course
approach unless a glide slope is specified on the approach
and landing chart.
7.4.2_The glide slope transmitter is located between
750 and 1,250 feet from the approach end of the
runway (down the runway) and offset 250-600 feet
from the runway centerline. It transmits a glide path
beam 1.4 degrees wide (vertically).
NOTE-
The term _glide path" means that portion of the glide slope
that intersects the localizer.
7.4.3_The glide path projection angle is normally
adjusted to 3 degrees above horizontal so that it
intersects the middle marker at about 200 feet and the
outer marker at about 1,400 feet above the runway
elevation. The glide slope is normally usable to the
distance of 10 NM. However, at some locations, the
AIP ENR 4.1-6
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
glide slope has been certified for an extended service
volume which exceeds 10 NM.
7.4.4_Pilots must be alert when approaching
glidepath interception. False courses and reverse
sensing will occur at angles considerably greater than
the published path.
7.4.5_Make every effort to remain on the indicated
glide path. Exercise caution: avoid flying below the
glide path to assure obstacle/terrain clearance is
maintained.
REFERENCE-
14 CFR Section 91.129(e).
7.4.6_A glide slope facility provides descent
information for navigation down to the lowest
authorized decision height (DH) specified in the
approved ILS approach procedure. The glidepath
may not be suitable for navigation below the lowest
authorized DH and any reference to glidepath
indications below that height must be supplemented
by visual reference to the runway environment. Glide
slopes with no published DH are usable to runway
threshold.
7.4.7_The published glide slope threshold crossing
height (TCH) DOES NOT represent the height of the
actual glide slope on course indication above the
runway threshold. It is used as a reference for
planning purposes which represents the height above
the runway threshold that an aircraft’s glide slope
antenna should be, if that aircraft remains on a
trajectory formed by the four-mile-to-middle
marker glidepath segment.
7.4.8_Pilots must be aware of the vertical height
between the aircraft’s glide slope antenna and the
main gear in the landing configuration and, at the DH,
plan to adjust the descent angle accordingly if the
published TCH indicates the wheel crossing height
over the runway threshold may be satisfactory. Tests
indicate a comfortable wheel crossing height is
approximately 20 to 30 feet, depending on the type of
aircraft.
NOTE-
The TCH for a runway is established based on several
factors including the largest aircraft category that
normally uses the runway, how airport layout effects the
glide slope antenna placement, and terrain. A higher than
optimum TCH, with the same glide path angle, may cause
the aircraft to touch down further from the threshold if the
trajectory of the approach is maintained until the flare.
Pilots should consider the effect of a high TCH on the
runway available for stopping the aircraft.
7.5_Distance Measuring Equipment (DME)
7.5.1_When installed with an ILS and specified in the
approach procedure, DME may be used:
7.5.1.1_In lieu of the outer marker.
7.5.1.2_As a back course final approach fix.
7.5.1.3_To establish other fixes on the localizer
course.
7.5.2_In some cases, DME from a separate facility
may be used within Terminal Instrument Procedures
(TERPS) limitations:
7.5.2.1_To provide ARC initial approach segments.
7.5.2.2_As a final approach fix for back course
approaches.
7.5.2.3_As a substitute for the outer marker.
7.6_Marker Beacon
7.6.1_ILS marker beacons have a rated power output
of 3 watts or less and an antenna array designed to
produce an elliptical pattern with dimensions, at
1,000 feet above the antenna, of approximately
2,400_feet in width and 4,200 feet in length. Airborne
marker beacon receivers with a selective sensitivity
feature should always be operated in the _low"
sensitivity position for proper reception of ILS
marker beacons.
7.6.2_Ordinarily, there are two marker beacons
associated with an ILS, the outer marker (OM) and
the middle marker (MM). Locations with a Category
II or III ILS also have an inner marker (IM). When an
aircraft passes over a marker, the pilot will receive the
following indications:
7.6.3_The OM normally indicates a position at which
an aircraft at the appropriate altitude on the localizer
course will intercept the ILS glide path.
7.6.4_The MM indicates a position approximately
3,500 feet from the landing threshold. This will also
be the position where an aircraft on the glide path will
be at an altitude of approximately 200 feet above the
elevation of the touchdown zone.
7.6.5_The IM indicates a point at which an aircraft is
at a designated decision height (DH) on the glide path
between the middle marker and landing threshold.
7.6.6_A back course marker, normally indicates the
ILS back course final approach fix where approach
descent is commenced.
AIP ENR 4.1-7
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
TBL ENR 4.1-1
Marker Passage Indications
Marker Code Light
OM _ _ _ BLUE
MM _ _ AMBER
IM WHITE
BC WHITE
8. Compass Locator
8.1_Compass locator transmitters are often situated
at the middle and outer marker sites. The transmitters
have a power of less than 25 watts, a range of at least
15 miles, and operate between 190 and 535 kHz. At
some locations, higher-powered radio beacons, up to
400 watts, are used as outer marker compass locators.
These generally carry Transcribed Weather Broadcast (TWEB) information.
8.2_Compass locators transmit two-letter identification groups. The outer locator transmits the first two
letters of the localizer identification group, and the
middle locator transmits the last two letters of the
localizer identification group.
9. ILS Frequency
9.1_The frequency pairs in TBL ENR 4.1-2 are
allocated for ILS.
TBL ENR 4.1-2
Frequency Pairs Allocated for ILS
Localizer MHz Glide Slope
108.10 334.70
108.15 334.55
108.3 334.10
108.35 333.95
108.5 329.90
108.55 329.75
108.7 330.50
108.75 330.35
108.9 329.30
108.95 329.15
109.1 331.40
109.15 331.25
109.3 332.00
109.35 331.85
109.50 332.60
109.55 332.45
109.70 333.20
109.75 333.05
109.90 333.80
109.95 333.65
110.1 334.40
110.15 334.25
110.3 335.00
110.35 334.85
110.5 329.60
110.55 329.45
110.70 330.20
110.75 330.05
110.90 330.80
110.95 330.65
111.10 331.70
111.15 331.55
111.30 332.30
111.35 332.15
111.50 332.9
111.55 332.75
111.70 333.5
111.75 333.35
111.90 331.1
111.95 330.95
AIP ENR 4.1-8
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
10. ILS Minimums
10.1_The lowest authorized ILS minimums, with all
required ground and airborne systems components
operative, are:
10.1.1_Category I._Decision Height (DH) 200 feet
and Runway Visual Range (RVR) 2,400 feet (with
touchdown zone and centerline lighting, RVR
1,800_feet).
10.1.2_Category II._DH 100 feet and RVR
1,200_feet.
10.1.3_Category IIIa._No DH or DH below 100 feet
and RVR not less than 700 feet.
10.1.4_Category IIIb._No DH or DH below 50 feet
and RVR less than 700 feet but not less than 150 feet.
10.1.5_Category IIIc._No DH or no RVR limitation.
NOTE-
Special authorization and equipment are required for
Category II and III.
11. Inoperative ILS Components
11.1_Inoperative Localizer._When the localizer
fails, an ILS approach is not authorized.
11.2_Inoperative Glide Slope._When the glide
slope fails, the ILS reverts to a nonprecision localizer
approach.
REFERENCE-
See the Inoperative Component Table in the U.S. Government Terminal
Procedures Publication (TPP) for adjustments to minimums due to
inoperative airborne or ground system equipment.
12. ILS Course Distortion
12.1_All pilots should be aware that disturbance to
ILS localizer/glide slope courses may occur when
surface vehicles/aircraft are operated near the
localizer/glide slope antennas. Most ILS installations
are subject to signal interference by either surface
vehicles, aircraft, or both. ILS _CRITICAL AREAS"
are established near each localizer and glide slope
antenna.
12.2_Air traffic control issues control instructions to
avoid interfering operations within ILS critical areas
at controlled airports during the hours the airport
traffic control tower is in operation as follows:
12.2.1_Weather Conditions._At or above 800 feet
and/or visibility 2 miles.
12.2.1.1_No critical area protection action is
provided.
12.2.1.2_If an aircraft advises the TOWER that an
_AUTOLAND"/_COUPLED" approach will be
conducted, an advisory will be promptly issued if a
vehicle/aircraft will be in or over a critical area when
the arriving aircraft is inside the ILS middle marker.
EXAMPLE-
Glide slope signal not protected.
12.2.2_Weather Conditions._Less than ceiling
800_feet and/or visibility 2 miles.
12.2.2.1_Glide Slope Critical Area._Vehicles/aircraft are not authorized in the area when an arriving
aircraft is between the ILS final approach fix and the
airport unless the aircraft has reported the airport in
sight and is circling or side stepping to land on other
than the ILS runway.
12.2.2.2_Localizer Critical Area._Except for aircraft that land, exit a runway, depart or miss approach,
vehicles and aircraft are not authorized in or over the
critical area when an arriving aircraft is between the
ILS final approach fix and the airport. Additionally,
when the ceiling is less than 200 feet and/or the
visibility is RVR 2,000 or less, vehicle/aircraft
operations in or over the area are not authorized when
an arriving aircraft is inside the ILS middle marker.
12.3_Aircraft holding below 5000 feet between the
outer marker and the airport may cause localizer
signal variations for aircraft conducting the ILS
approach. Accordingly, such holding is not authorized when weather or visibility conditions are less
than ceiling 800 feet and/or visibility 2 miles.
12.4_Pilots are cautioned that vehicular traffic not
subject to control by ATC may cause momentary
deviation to ILS course/glide slope signals. Also,
_critical areas" are not protected at uncontrolled
airports or at airports with an operating control tower
when weather/visibility conditions are above those
requiring protective measures. Aircraft conducting
_coupled" or _autoland" operations should be
especially alert in monitoring automatic flight control
systems. (See FIG ENR 4.1-2.)
NOTE-
Unless otherwise coordinated through flight standards,
ILS signals to Category 1 runways are not flight inspected
below 100 feet AGL. Guidance signal anomalies may be
encountered below this altitude.
AIP ENR 4.1-9
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1-2
FAA Instrument Landing Systems
AIP ENR 4.1-10
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
13. Continuous Power Facilities
13.1_In order to ensure that a basic ATC system
remains in operation despite an area wide or
catastrophic commercial power failure, key equipment and certain airports have been designated to
provide a network of facilities whose operational
capability can be utilized independent of any
commercial power supply.
13.2_In addition to those facilities comprising the
basic ATC system, the following approach and
lighting aids have been included in this program for
a selected runway:
13.2.1_ILS (Localizer, Glide Slope, Compass
Locator, Inner, Middle and Outer Markers).
13.2.2_Wind Measuring Capability.
13.2.3_Approach Light System (ALS) or Short ALS
(SALS).
13.2.4_Ceiling Measuring Capability.
13.2.5_Touchdown Zone Lighting (TDZL).
13.2.6_Centerline Lighting (CL).
13.2.7_Runway Visual Range (RVR).
13.2.8_High Intensity Runway Lighting (HIRL).
13.2.9_Taxiway Lighting.
13.2.10_Apron Light (Perimeter Only).
TBL ENR 4.1-3
Continuous Power Airports
Airport/Ident Runway No.
Albuquerque (ABQ) 08
Andrews AFB (ADW) 1L
Atlanta (ATL) 9R
Baltimore (BWI) 10
Bismarck (BIS) 31
Boise (BOI) 10R
Boston (BOS) 4R
Charlotte (CLT) 36L
Chicago (ORD) 14R
Cincinnati (CVG) 36
Cleveland (CLE) 5R
Dallas/Fort Worth (DFW) 17L
Denver (DEN) 35R
Des Moines (DSM) 30R
Detroit (DTW) 3L
Continuous Power Airports
Airport/Ident Runway No.
El Paso (ELP) 22
Great Falls (GTF) 03
Houston (IAH) 08
Indianapolis (IND) 4L
Jacksonville (JAX) 07
Kansas City (MCI) 19
Los Angeles (LAX) 24R
Memphis (MEM) 36L
Miami (MIA) 9L
Milwaukee (MKE) 01
Minneapolis (MSP) 29L
Nashville (BNA) 2L
Newark (EWR) 4R
New Orleans (MSY) 10
New York (JFK) 4R
New York (LGA) 22
Oklahoma City (OKC) 35R
Omaha (OMA) 14
Ontario, California (ONT) 26R
Philadelphia (PHL) 9R
Phoenix (PHX) 08R
Pittsburgh (PIT) 10L
Reno (RNO) 16
Salt Lake City (SLC) 34L
San Antonio (SAT) 12R
San Diego (SAN) 09
San Francisco (SFO) 28R
Seattle (SEA) 16R
St. Louis (STL) 24
Tampa (TPA) 36L
Tulsa (TUL) 35R
Washington (DCA) 36
Washington (IAD) 1R
Wichita (ICT) 01
13.3_The above have been designated _Continuous
Power Airports," and have independent back up
capability for the equipment installed.
NOTE-
The existing CPA runway is listed. Pending and future
changes at some locations will require a revised runway
designation.
AIP ENR 4.1-11
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
14. Simplified Directional Facility (SDF)
14.1_The SDF provides a final approach course
similar to that of the ILS localizer. It does not provide
glide slope information. A clear understanding of the
ILS localizer and the additional factors listed below
completely describe the operational characteristics
and use of the SDF.
14.2_The SDF transmits signals within the range of
108.10 to 111.95 MHz.
14.3_The approach techniques and procedures used
in an SDF instrument approach are essentially the
same as those employed in executing a standard
no-glide-slope localizer approach except the SDF
course may not be aligned with the runway and the
course may be wider, resulting in less precision.
14.4_Usable off-course indications are limited to
35_degrees either side of the course centerline.
Instrument indications received beyond 35 degrees
should be disregarded.
14.5_The SDF antenna may be offset from the
runway centerline. Because of this, the angle of
convergence between the final approach course and
the runway bearing should be determined by
reference to the instrument approach procedure chart.
This angle is generally not more than 3 degrees.
However, it should be noted that inasmuch as the
approach course originates at the antenna site, an
approach which is continued beyond the runway
threshold will lead the aircraft to the SDF offset
position rather than along the runway centerline.
14.6_The SDF signal is fixed at either 6 degrees or
12_degrees as necessary to provide maximum _fly
ability" and optimum course quality.
14.7_Identification consists of a three-letter identifier transmitted in Morse Code on the SDF frequency.
The appropriate instrument approach chart will
indicate the identifier used at a particular airport.
15. Microwave Landing System (MLS)
15.1_General
15.1.1_The MLS provides precision navigation
guidance for exact alignment and descent of aircraft
on approach to a runway. It provides azimuth,
elevation, and distance information. The elevation
transmitter is located to the side of the runway near
the approach threshold. The precision DME, which
provides range information, is normally collocated
with the azimuth transmitter.
15.1.2_Both lateral and vertical guidance may be
displayed on conventional course deviation indicators or incorporated into multipurpose cockpit
displays. Range information can be displayed by
conventional DME indicators and also incorporated
into multipurpose displays.
15.1.3_The MLS supplements the ILS as the standard
landing system in the U.S. for civil, military, and
international civil aviation. At international airports,
ILS service is protected to 2010.
15.1.4_The system may be divided into five
functions:
15.1.4.1_Approach azimuth.
15.1.4.2_Back azimuth.
15.1.4.3_Approach elevation.
15.1.4.4_Range.
15.1.4.5_Data communications.
15.1.5_The standard configuration of MLS ground
equipment includes:
15.1.5.1_An azimuth station to perform functions
15.1.4.1 and 15.1.4.5 above. In addition to providing
azimuth navigation guidance, the azimuth station
also transmits basic data which consists of
information associated directly with the operation of
the landing system, as well as advisory data on the
performance of the ground equipment.
15.1.5.2_An elevation station to perform function
15.1.4.3.
15.1.5.3_Distance Measuring Equipment (DME) to
perform function 15.1.4.4. The DME provides range
guidance, both standard (DME/N) and precision
DME (DME/P).
15.1.6_MLS Expansion Capabilities._The standard configuration can be expanded by adding one or
more of the following functions or characteristics.
15.1.6.1_Back Azimuth._Provides lateral guidance
for missed approach and departure navigation.
15.1.6.2_Auxiliary Data Transmissions._Provides
additional data, including refined airborne positioning, meteorological information, runway status, and
other supplementary information.
15.1.6.3_Expanded Service Volume (ESV).
Provides proportional guidance to 60 degrees.
AIP ENR 4.1-12
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
15.1.7_MLS identification is a four-letter designation starting with the letter M. It is transmitted in
Morse Code at least six times per minute by the
approach azimuth (and back azimuth) ground
equipment.
15.2_Approach Azimuth Guidance
15.2.1_The azimuth station transmits MLS angle and
data on one of the 200 channels within the frequency
range of 5031 to 5091 MHz.
15.2.2_The equipment is normally located about
1,000 feet beyond the stop end of the runway, but
there is considerable flexibility in selecting sites. For
example, for heliport operations the azimuth
transmitter can be collocated with the elevation
transmitter.
15.2.3_The azimuth coverage extends:
(See FIG ENR 4.1-3.)
FIG ENR 4.1-3
Coverage Volume
Azimuth
APPROACH
AZIMUTH
AZIMUTH
-40°
+40°
20 NM
ESV
ESV
14 NM
+60°
MAXIMUM LIMIT
14 NM
-60°
15.2.3.1_Laterally, at least 40 degrees on either side
of the runway centerline in a standard configuration.
15.2.3.2_In elevation, up to an angle of 15 degrees -
and to at least 20,000 feet.
15.2.3.3_In range, to at least 20 NM.
15.3_Elevation Guidance
15.3.1_The elevation station transmits signals on the
same frequency as the azimuth station. A single
frequency is time-shared between all angle and data
functions.
15.3.2_The elevation transmitter is normally located
about 400 feet from the side of the runway between
runway threshold and the touchdown zone.
15.3.3_Elevation coverage is provided in the same
airspace as the azimuth guidance signals:
15.3.3.1_In elevation, to at least +15 degrees.
15.3.3.2_Laterally, to fill the azimuth lateral
coverage.
15.3.3.3_In range, to at least 20 NM. (See
FIG ENR 4.1-4.)
FIG ENR 4.1-4
Coverage Volumes
Elevation
ELEVATION
NORMAL
GLIDE PATH
MAXIMUM LIMIT 20,000’
20 NM 30
3
15
o
o
o
o
15.4_Range Guidance
15.4.1_The MLS Precision Distance Measuring
Equipment (DME/P) functions the same as the
navigation DME, but with some technical differences. The beacon transponder operates in the
frequency band 962 to 1105 MHz and responds to an
aircraft interrogator. The MLS DME/P accuracy is
improved to be consistent with the accuracy provided
by the MLS azimuth and elevation stations.
15.4.2_A DME/P channel is paired with the azimuth
and elevation channel. A complete listing of the 200
paired channels of the DME/P with the angle
functions is contained in FAA Standard 022 (MLS
Interoperability and Performance Requirements).
AIP ENR 4.1-13
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
15.4.3_The DME/N or DME/P is an integral part of
the MLS and is installed at all MLS facilities unless
a waiver is obtained. This occurs infrequently and
only at outlying, low density airports where marker
beacons or compass locators are already in place.
15.5_Data Communications
15.5.1_The data transmission can include both the
basic and auxiliary data words. All MLS facilities
transmit basic data. Where needed, auxiliary data can
be transmitted.
15.5.2_Coverage Limits._MLS data are transmitted
throughout the azimuth (and back azimuth when
provided) coverage sectors.
15.5.3_Basic Data Content._Representative data
include:
15.5.3.1_Station identification.
15.5.3.2_Exact locations of azimuth, elevation and
DME/P stations (for MLS receiver processing
functions).
15.5.3.3_Ground equipment performance level.
15.5.3.4_DME/P channel and status.
15.5.4_Auxiliary Data Content._Representative
data include:
15.5.4.1_3-D locations of MLS equipment.
15.5.4.2_Waypoint coordinates.
15.5.4.3_Runway conditions.
15.5.4.4_Weather (e.g., RVR, ceiling, altimeter
setting, wind, wake vortex, wind shear).
15.6_Operational Flexibility._The MLS has the
capability to fulfill a variety of needs in the approach,
landing, missed approach, and departure phases of
flight. For example:
15.6.1_Curved and segmented approaches.
15.6.2_Selectable glide path angles.
15.6.3_Accurate 3-D positioning of the aircraft in
space.
15.6.4_The establishment of boundaries to ensure
clearance from obstructions in the terminal area.
15.7_While many of these capabilities are available
to any MLS-equipped aircraft, the more sophisti-
cated capabilities (such as curved and segmented
approaches) are dependent upon the particular
capabilities of the airborne equipment.
15.8_Summary
15.8.1_Accuracy._The MLS provides precision,
three-dimensional navigation guidance accurate
enough for all approach and landing maneuvers.
15.8.2_Coverage._Accuracy is consistent throughout the coverage volumes shown in FIG ENR 4.1-5.
FIG ENR 4.1-5
Coverage Volumes
3-D Representation
15.8.3_Environment._The system has low susceptibility to interference from weather conditions and
airport ground traffic.
15.8.4_Channels._MLS has 200 channels - enough
for any foreseeable need.
15.8.5_Data._The MLS transmits ground-air data
messages associated with system operation.
15.8.6_Range Information._Continuous range information is provided with an accuracy of about
100_feet.
AIP ENR 4.1-14
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
16. LORAN
16.1_Introduction
16.1.1_The LOng RAnge Navigation-C (LORAN)
system is a hyperbolic, terrestrial-based navigation
system operating in the 90-110 kHz frequency band.
LORAN, operated by the U.S. Coast Guard (USCG),
has been in service for over 50 years and is used for
navigation by the various transportation modes, as
well as, for precise time and frequency applications.
The system is configured to provide reliable, all
weather navigation for marine users along the U.S.
coasts and in the Great Lakes.
16.1.2_In the 1980’s, responding to aviation user and
industry requests, the USCG and FAA expanded
LORAN coverage to include the entire continental
U.S. This work was completed in late 1990, but the
LORAN system failed to gain significant user
acceptance and primarily due to transmitter and user
equipment performance limitations, attempts to
obtain FAA certification of nonprecision approach
capable receivers were unsuccessful. More recently,
concern regarding the vulnerability of Global
Positioning System (GPS) and the consequences of
losing GPS on the critical U.S. infrastructure
(e.g.,_NAS) has renewed and refocused attention on
LORAN.
16.1.3_LORAN is also supported in the Canadian
airspace system. Currently, LORAN receivers are
only certified for en route navigation.
16.1.4_Additional information can be found in the
_LORAN-C User Handbook," COMDT PUBP
16562.6, or the website:
http://www.navcen.uscg.gov.
16.2_LORAN Chain
16.2.1_The locations of the U.S. and Canadian
LORAN transmitters and monitor sites are illustrated
in FIG ENR 4.1-6. Station operations are organized
into subgroups of four to six stations called _chains."
One station in the chain is designated the _Master"
and the others are _secondary" stations. The resulting
chain based coverage is seen in FIG ENR 4.1-7.
FIG ENR 4.1-6
U.S. and Canadian LORAN System Architecture
AIP ENR 4.1-15
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1-7
LORAN Chain Based Coverage
16.2.2_The LORAN navigation signal is a carefully
structured sequence of brief radio frequency pulses
centered at 100 kHz. The sequence of signal
transmissions consists of a pulse group from the
Master (M) station followed at precise time intervals
by groups from the secondary stations, which are
designated by the U.S. Coast Guard with the letters V,
W, X, Y and Z. All secondary stations radiate pulses
in groups of eight, but for identification the Master
signal has an additional ninth pulse. (See
FIG ENR 4.1-8.) The timing of the LORAN system
is tightly controlled and synchronized to Coordinated
Universal Time (UTC). Like the GPS, this is a
Stratum_1 timing standard.
16.2.3_The time interval between the reoccurrence of
the Master pulse group is called the Group Repetition
Interval (GRI). The GRI is the same for all stations in
a chain and each LORAN chain has a unique GRI.
Since all stations in a particular chain operate on the
same radio frequency, the GRI is the key by which a
LORAN receiver can identify and isolate signal
groups from a specific chain.
EXAMPLE-
Transmitters in the Northeast U.S. chain (FIG ENR 4.1-9)
operate with a GRI of 99,600 microseconds which is
shortened to 9960 for convenience. The master station (M)
at Seneca, New York, controls secondary stations (W) at
Caribou, Maine; (X) at Nantucket, Massachusetts; (Y) at
Carolina Beach, North Carolina, and (Z) at Dana, Indiana.
In order to keep chain operations precise, monitor
receivers are located at Cape Elizabeth, ME; Sandy Hook,
NJ; Dunbar Forest, MI, and Plumbrook, OH. Monitor
receivers continuously measure various aspects of the
quality (e.g., pulse shape) and accuracy (e.g., timing) of
LORAN signals and report system status to a control
station.
16.2.4_The line between the Master and each
secondary station is the _baseline" for a pair of
stations. Typical baselines are from 600 to
1000_nautical miles in length. The continuation of the
baseline in either direction is a _baseline extension."
16.2.5_At the LORAN transmitter stations there are
cesium oscillators, transmitter time and control
equipment, a transmitter, primary power (e.g.,_commercial or generator) and auxiliary power equipment
(e.g., uninterruptible power supplies and generators),
and a transmitting antenna (configurations may either
have 1 or 4 towers) with the tower heights ranging
from 700 to 1350 feet tall. Depending on the coverage
area requirements a LORAN station transmits from
400 to 1,600 kilowatts of peak signal power.
16.2.6_The USCG operates the LORAN transmitter
stations under a reduced staffing structure that is
made possible by the remote control and monitoring
of the critical station and signal parameters. The
actual control of the transmitting station is
AIP ENR 4.1-16
United States of America 15 MAR 07
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Nineteenth Edition
accomplished remotely at Coast Guard Navigation
Center (NAVCEN) located in Alexandria, Virginia.
East Coast and Midwest stations are controlled by the
NAVCEN. Stations on the West Coast and in Alaska
are controlled by the NAVCEN Detachment (Det),
located in Petaluma, California. In the event of a
problem at one of these two 24 hour-a-day staffed
sites, monitoring and control of the entire LORAN
system can be done at either location. If both NACEN
and NAVCEN Det are down or if there is an
equipment problem at a specific station, local station
personnel are available to operate and perform repairs
at each LORAN station.
16.2.7_The transmitted signal is also monitored in the
service areas (i.e., area of published LORAN
coverage) and its status provided to NAVCEN and
NAVCEN Det. The System Area Monitor (SAM) is
a single site used to observe the transmitted signal
(signal strength, time difference, and pulse shape). If
an out-of-tolerance situation that could affect
navigation accuracy is detected, an alert signal called
_Blink" is activated. Blink is a distinctive change in
the group of eight pulses that can be recognized
automatically by a receiver so the user is notified
instantly that the LORAN system should not be used
for navigation. Out-of-tolerance situations which
only the local station can detect are also monitored.
These situations when detected cause signal
transmissions from a station to be halted.
16.2.8_Each individual LORAN chain provides
navigation-quality signal coverage over an identified
area as shown in FIG ENR 4.1-10 for the West Coast
chain, GRI 9940. The chain Master station is at
Fallon, Nevada, and secondary stations are at George,
Washington; Middletown, California, and Searchlight, Nevada. In a signal coverage area the signal
strength relative to the normal ambient radio noise
must be adequate to assure successful reception.
Similar coverage area charts are available for all
chains.
AIP ENR 4.1-17
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1-8
The LORAN Pulse and Pulse Group
AIP ENR 4.1-18
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Federal Aviation Administration
Nineteenth Edition
FIG ENR 4.1-9
Northeast U.S. LORAN Chain
AIP ENR 4.1-19
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1-10
West Coast U.S. LORAN Chain
AIP ENR 4.1-20
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Federal Aviation Administration
Nineteenth Edition
16.3_The LORAN Receiver
16.3.1_For a currently certified LORAN aviation
receiver to provide navigation information for a pilot,
it must successfully receive, or _acquire," signals
from three or more stations in a chain. Acquisition
involves the time synchronization of the receiver with
the chain GRI, identification of the Master station
signals from among those checked, identification of
secondary station signals, and the proper selection of
the tracking point on each signal at which
measurements are made. However, a new generation
of receivers has been developed that use pulses from
all stations that can be received at the pilot’s location.
Use of _all-in-view" stations by a receiver is made
possible due to the synchronization of LORAN
stations signals to UTC. This new generation of
receivers, along with improvements at the transmitting stations and changes in system policy and
operations doctrine may allow for LORAN’s use in
nonprecision approaches. At this time these receivers
are available for purchase, but none have been
certified for aviation use.
16.3.2_The basic measurements made by certified
LORAN receivers are the differences in time-of-arrival between the Master signal and the signals from
each of the secondary stations of a chain. Each _time
difference" (TD) value is measured to a precision of
about 0.1 microseconds. As a rule of thumb,
0.1_microsecond is equal to about 100 feet.
16.3.3_An aircraft’s LORAN receiver must recognize three signal conditions:
16.3.3.1_Usable signals;
16.3.3.2_Absence of signals, and
16.3.3.3_Signal blink.
16.3.4_The most critical phase of flight is during the
approach to landing at an airport. During the
approach phase the receiver must detect a lost signal,
or a signal Blink, within 10 seconds of the occurrence
and warn the pilot of the event. At this time there are
no receivers that are certified for nonprecision
approaches.
16.3.5_Most certified receivers have various internal
tests for estimating the probable accuracy of the
current TD values and consequent navigation
solutions. Tests may include verification of the timing
alignment of the receiver clock with the LORAN
pulse, or a continuous measurement of the signal-
to-noise ratio (SNR). SNR is the relative strength of
the LORAN signals compared to the local ambient
noise level. If any of the tests fail, or if the quantities
measured are out of the limits set for reliable
navigation, then an alarm will be activated to alert the
pilot.
16.3.6_LORAN signals operate in the low frequency
band (90-110 kHz) that has been reserved for marine
navigation signals. Adjacent to the band, however,
are numerous low frequency communications
transmitters. Nearby signals can distort the LORAN
signals and must be eliminated by the receiver to
assure proper operation. To eliminate interfering
signals, LORAN receivers have selective internal
filters. These filters, commonly known as _notch
filters," reduce the effect of interfering signals.
16.3.7_Careful installation of antennas, good metal-
to-metal electrical bonding, and provisions for
precipitation noise discharge on the aircraft are
essential for the successful operation of LORAN
receivers. A LORAN antenna should be installed on
an aircraft in accordance with the manufacturer’s
instructions. Corroded bonding straps should be
replaced, and static discharge devices installed at
points indicated by the aircraft manufacturer.
16.4_LORAN Navigation
16.4.1_An airborne LORAN receiver has four major
parts:
16.4.1.1_Signal processor;
16.4.1.2_Navigation computer;
16.4.1.3_Control/display, and
16.4.1.4_Antenna.
16.4.2_The signal processor acquires LORAN
signals and measures the difference between the
time-of-arrival of each secondary station pulse
group and the Master station pulse group. The
measured TDs depend on the location of the receiver
in relation to the three or more transmitters.
AIP ENR 4.1-21
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG ENR 4.1-11
First Line-of-Position
16.4.2.1_The first TD will locate an aircraft
somewhere on a line-of-position (LOP) on which the
receiver will measure the same TD value.
16.4.2.2_A second LOP is defined by a TD
measurement between the Master station signal and
the signal form another secondary station.
FIG ENR 4.1-12
Second Line-of-Position
16.4.2.3_The intersection of the measured LOPs is
the position of the aircraft.
FIG ENR 4.1-13
Intersection of Lines-of-Position
16.4.3_The navigation computer converts TD values
to corresponding latitude and longitude. Once the
time and position of the aircraft are established at
two_points, distance to destination, cross track error,
ground speed, estimated time of arrival, etc., can be
determined. Cross track error can be displayed as the
vertical needle of a course deviation indicator, or
digitally, as decimal parts of a mile left or right of
course.
16.5_Notices to Airmen (NOTAMs) are issued for
LORAN chain or station outages. Domestic
NOTAM_(D)s are issued under the identifier _LRN."
International NOTAMs are issued under the KNMH
series. Pilots may obtain these NOTAMs from FSS
briefers upon request.
16.6_LORAN Status Information._To find out
more information on the LORAN system and its
operational status you can visit the website
http://www.navcen.uscg.gov/loran/default.htm or
contact NAVCEN’s Navigation Information Service
(NIS) watchstander, phone_(703) 313-5900,
fax_(703) 313-5920.
16.7_LORAN’s future._The U.S. will continue to
operate the LORAN system in the short term. During
this time, the FAA LORAN evaluation program,
AIP ENR 4.1-22
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Nineteenth Edition
being conducted with the support of a team
comprising government, academia, and industry, will
identify and assess LORAN’s potential contributions
to required navigation services for the National
Airspace System (NAS), and support decisions
regarding continued operation of the system. If the
government concludes LORAN should not be kept as
part of the mix of federally provided radio navigation
systems, it will give the users of LORAN reasonable
notice so that they will have the opportunity to
transition to alternative navigation aids.
17. Inertial Reference Unit (IRU), Inertial
Navigation System (INS), and Attitude
Heading Reference System (AHRS)
17.1_IRUs are self-contained systems comprised of
gyros and accelerometers that provide aircraft
attitude (pitch, roll, and heading), position, and
velocity information in response to signals resulting
from inertial effects on system components. Once
aligned with a known position, IRUs continuously
calculate position and velocity. IRU position
accuracy decays with time. This degradation is
known as _drift."
17.2_INSs combine the components of an IRU with
an internal navigation computer. By programming a
series of waypoints, these systems will navigate along
a predetermined track.
17.3_AHRSs are electronic devices that provide
attitude information to aircraft systems such as
weather radar and autopilot, but do not directly
compute position information.
18. Global Positioning System (GPS)
18.1_System Overview
18.1.1_System Description. The Global Positioning
System is a satellite-based radio navigation system,
which broadcasts a signal that is used by receivers to
determine precise position anywhere in the world.
The receiver tracks multiple satellites and determines
a pseudorange measurement that is then used to
determine the user location. A minimum of four
satellites is necessary to establish an accurate
three-dimensional position. The Department of
Defense (DOD) is responsible for operating the GPS
satellite constellation and monitors the GPS satellites
to ensure proper operation. Every satellite’s orbital
parameters (ephemeris data) are sent to each satellite
for broadcast as part of the data message embedded
in the GPS signal. The GPS coordinate system is the
Cartesian earth-centered earth-fixed coordinates as
specified in the World Geodetic System 1984
(WGS-84).
18.1.2_System Availability and Reliability
18.1.2.1_The status of GPS satellites is broadcast as
part of the data message transmitted by the GPS
satellites. GPS status information is also available by
means of the U.S. Coast Guard navigation
information service: (703) 313-5907, Internet:
http://www.navcen.uscg.gov/. Additionally, satellite status is available through the Notice to Airmen
(NOTAM) system.
18.1.2.2_The operational status of GNSS operations
depends upon the type of equipment being used. For
GPS-only equipment TSO-C129a, the operational
status of nonprecision approach capability for flight
planning purposes is provided through a prediction
program that is embedded in the receiver or provided
separately.
18.1.3_Receiver Autonomous Integrity Monitoring
(RAIM). When GNSS equipment is not using
integrity information from WAAS or LAAS, the GPS
navigation receiver using RAIM provides GPS signal
integrity monitoring. RAIM is necessary since delays
of up to two hours can occur before an erroneous
satellite transmission can be detected and corrected
by the satellite control segment. The RAIM function
is also referred to as fault detection. Another
capability, fault exclusion, refers to the ability of the
receiver to exclude a failed satellite from the position
solution and is provided by some GPS receivers and
by WAAS receivers.
18.1.4_The GPS receiver verifies the integrity
(usability) of the signals received from the GPS
constellation through receiver autonomous integrity
monitoring (RAIM) to determine if a satellite is
providing corrupted information. At least one
satellite, in addition to those required for navigation,
must be in view for the receiver to perform the RAIM
function; thus, RAIM needs a minimum of 5 satellites
in view, or 4 satellites and a barometric altimeter
(baro-aiding) to detect an integrity anomaly. For
receivers capable of doing so, RAIM needs
6_satellites in view (or 5 satellites with baro-aiding)
to isolate the corrupt satellite signal and remove it
from the navigation solution. Baro-aiding is a
method of augmenting the GPS integrity solution by
using a nonsatellite input source. GPS derived
AIP ENR 4.1-23
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
altitude should not be relied upon to determine
aircraft altitude since the vertical error can be quite
large and no integrity is provided. To ensure that
baro-aiding is available, the current altimeter setting
must be entered into the receiver as described in the
operating manual.
18.1.5_RAIM messages vary somewhat between
receivers; however, generally there are two types.
One type indicates that there are not enough satellites
available to provide RAIM integrity monitoring and
another type indicates that the RAIM integrity
monitor has detected a potential error that exceeds the
limit for the current phase of flight. Without RAIM
capability, the pilot has no assurance of the accuracy
of the GPS position.
18.1.6_Selective Availability. Selective Availability
(SA) is a method by which the accuracy of GPS is
intentionally degraded. This feature is designed to
deny hostile use of precise GPS positioning data. SA
was discontinued on May 1, 2000, but many GPS
receivers are designed to assume that SA is still
active. New receivers may take advantage of the
discontinuance of SA based on the performance
values in ICAO Annex 10, and do not need to be
designed to operate outside of that performance.
18.1.7_The GPS constellation of 24 satellites is
designed so that a minimum of five is always
observable by a user anywhere on earth. The receiver
uses data from a minimum of four satellites above the
mask angle (the lowest angle above the horizon at
which it can use a satellite).
18.1.8_The DOD declared initial operational capability (IOC) of the U.S. GPS on December 8, 1993.
The FAA has granted approval for U.S. civil
operators to use properly certified GPS equipment as
a primary means of navigation in oceanic airspace
and certain remote areas. Properly certified GPS
equipment may be used as a supplemental means of
IFR navigation for domestic en route, terminal
operations, and certain instrument approach procedures (IAPs). This approval permits the use of GPS
in a manner that is consistent with current navigation
requirements as well as approved air carrier
operations specifications.
18.2_VFR Use of GPS
18.2.1_GPS navigation has become a great asset to
VFR pilots, providing increased navigation capability and enhanced situational awareness, while
reducing operating costs due to greater ease in flying
direct routes. While GPS has many benefits to the
VFR pilot, care must be exercised to ensure that
system capabilities are not exceeded._
18.2.2_Types of receivers used for GPS navigation
under VFR are varied, from a full IFR installation
being used to support a VFR flight, to a VFR only
installation (in either a VFR or IFR capable aircraft)
to a hand-held receiver. The limitations of each type
of receiver installation or use must be understood by
the pilot to avoid misusing navigation information.
(See TBL ENR 4.1-5.) In all cases, VFR pilots
should never rely solely on one system of navigation.
GPS navigation must be integrated with other forms
of electronic navigation (when possible), as well as
pilotage and dead reckoning. Only through the
integration of these techniques can the VFR pilot
ensure accuracy in navigation.
18.2.3_Some critical concerns in VFR use of GPS
include RAIM capability, database currency, and
antenna location.
18.2.3.1_RAIM Capability._Many VFR GPS receivers and all hand-held units have no RAIM
alerting capability. Loss of the required number of
satellites in view, or the detection of a position error,
cannot be displayed to the pilot by such receivers. In
receivers with no RAIM capability, no alert would be
provided to the pilot that the navigation solution had
deteriorated, and an undetected navigation error
could occur. A systematic cross-check with other
navigation techniques would identify this failure, and
prevent a serious deviation. See subparagraphs 18.1.6
and 18.1.7 for more information on RAIM.
18.2.3.2_Database Currency
a)_In many receivers, an updateable database is
used for navigation fixes, airports, and instrument
procedures. These databases must be maintained to
the current update for IFR operation, but no such
requirement exists for VFR use.
b)_However, in many cases, the database drives a
moving map display which indicates Special Use
Airspace and the various classes of airspace, in
addition to other operational information. Without a
current database the moving map display may be
outdated and offer erroneous information to VFR
pilots wishing to fly around critical airspace areas,
such as a Restricted Area or a Class B airspace
segment. Numerous pilots have ventured into
airspace they were trying to avoid by using an
AIP ENR 4.1-24
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Nineteenth Edition
outdated database. If you don’t have a current
database in the receiver, disregard the moving map
display for critical navigation decisions.
c)_In addition, waypoints are added, removed,
relocated, or renamed as required to meet operational
needs. When using GPS to navigate relative to a
named fix, a current database must be used to
properly locate a named waypoint. Without the
update, it is the pilot’s responsibility to verify the
waypoint location referencing to an official current
source, such as the Airport/Facility Directory,
Sectional Chart, or En Route Chart.
18.2.3.3_Antenna Location
a)_In many VFR installations of GPS receivers,
antenna location is more a matter of convenience than
performance. In IFR installations, care is exercised to
ensure that an adequate clear view is provided for the
antenna to see satellites. If an alternate location is
used, some portion of the aircraft may block the view
of the antenna, causing a greater opportunity to lose
navigation signal.
b)_This is especially true in the case of hand-helds.
The use of hand-held receivers for VFR operations is
a growing trend, especially among rental pilots.
Typically, suction cups are used to place the GPS
antennas on the inside of cockpit windows. While
this method has great utility, the antenna location is
limited to the cockpit or cabin only and is rarely
optimized to provide a clear view of available
satellites. Consequently, signal losses may occur in
certain situations of aircraft-satellite geometry,
causing a loss of navigation signal. These losses,
coupled with a lack of RAIM capability, could
present erroneous position and navigation information with no warning to the pilot.
c)_While the use of a hand-held GPS for VFR
operations is not limited by regulation, modification
of the aircraft, such as installing a panel- or
yoke-mounted holder, is governed by 14 CFR
Part_43. Consult with your mechanic to ensure
compliance with the regulation, and a safe
installation.
18.2.4_As a result of these and other concerns, here
are some tips for using GPS for VFR operations:
18.2.4.1_Always check to see if your unit has RAIM
capability. If no RAIM capability exists, be
suspicious of your GPS position when any
disagreement exists with the position derived from
other radio navigation systems, pilotage, or dead
reckoning.
18.2.4.2_Check the currency of the database, if any.
If expired, update the database using the current
revision. If an update of an expired database is not
possible, disregard any moving map display of
airspace for critical navigation decisions. Be aware
that named waypoints may no longer exist or may
have been relocated since the database expired. At a
minimum, the waypoints planned to be used should
be checked against a current official source, such as
the Airport/Facility Directory, or a Sectional
Aeronautical Chart.
18.2.4.3_While hand-helds can provide excellent
navigation capability to VFR pilots, be prepared for
intermittent loss of navigation signal, possibly with
no RAIM warning to the pilot. If mounting the
receiver in the aircraft, be sure to comply with
14_CFR Part 43.
18.2.4.4_Plan flights carefully before taking off. If
you wish to navigate to user-defined waypoints,
enter them before flight, not on-the-fly. Verify your
planned flight against a current source, such as a
current sectional chart. There have been cases in
which one pilot used waypoints created by another
pilot that were not where the pilot flying was
expecting. This generally resulted in a navigation
error. Minimize head-down time in the aircraft and
keep a sharp lookout for traffic, terrain, and obstacles.
Just a few minutes of preparation and planning on the
ground will make a great difference in the air.
18.2.4.5_Another way to minimize head-down time
is to become very familiar with your receiver’s
operation. Most receivers are not intuitive. The pilot
must take the time to learn the various keystrokes,
knob functions, and displays that are used in the
operation of the receiver. Some manufacturers
provide computer-based tutorials or simulations of
their receivers. Take the time to learn about your
particular unit before you try to use it in flight.
18.2.5_In summary, be careful not to rely on GPS to
solve all your VFR navigational problems. Unless an
IFR receiver is installed in accordance with IFR
requirements, no standard of accuracy or integrity has
been assured. While the practicality of GPS is
compelling, the fact remains that only the pilot can
navigate the aircraft, and GPS is just one of the pilot’s
tools to do the job.
AIP ENR 4.1-25
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18.3_VFR Waypoints
18.3.1_VFR waypoints provide VFR pilots with a
supplementary tool to assist with position awareness
while navigating visually in aircraft equipped with
area navigation receivers. VFR waypoints should be
used as a tool to supplement current navigation
procedures. The uses of VFR waypoints include
providing navigational aids for pilots unfamiliar with
an area, waypoint definition of existing reporting
points, enhanced navigation in and around Class B
and Class C airspace, and enhanced navigation
around Special Use Airspace. VFR pilots should rely
on appropriate and current aeronautical charts
published specifically for visual navigation. If
operating in a terminal area, pilots should take
advantage of the Terminal Area Chart available for
that area, if published. The use of VFR waypoints
does not relieve the pilot of any responsibility to
comply with the operational requirements of 14 CFR
Part 91.
18.3.2_VFR waypoint names (for computer-entry
and flight plans) consist of five letters beginning with
the letters _VP" and are retrievable from navigation
databases. The VFR waypoint names are not intended
to be pronounceable, and they are not for use in ATC
communications. On VFR charts, stand-alone VFR
waypoints will be portrayed using the same
four-point star symbol used for IFR waypoints. VFR
waypoints collocated with visual check points on the
chart will be identified by small magenta flag
symbols. VFR waypoints collocated with visual
check points will be pronounceable based on the
name of the visual check point and may be used for
ATC communications. Each VFR waypoint name
will appear in parentheses adjacent to the geographic
location on the chart. Latitude/longitude data for all
established VFR waypoints may be found in the
appropriate regional Airport/Facility Directory
(A/FD).
18.3.3_VFR waypoints shall not be used to plan
flights under IFR. VFR waypoints will not be
recognized by the IFR system and will be rejected for
IFR routing purposes.
18.3.4_When filing VFR flight plans, pilots may use
the five letter identifier as a waypoint in the route of
flight section if there is an intended course change at
that point or if used to describe the planned route of
flight. This VFR filing would be similar to how a
VOR would be used in a route of flight. Pilots must
use the VFR waypoints only when operating under
VFR conditions.
18.3.5_Any VFR waypoints intended for use during
a flight should be loaded into the receiver while on the
ground and prior to departure. Once airborne, pilots
should avoid programming routes or VFR waypoint
chains into their receivers.
18.3.6_Pilots should be especially vigilant for other
traffic while operating near VFR waypoints. The
same effort to see and avoid other aircraft near VFR
waypoints will be necessary, as was the case with
VORs and NDBs in the past. In fact, the increased
accuracy of navigation through the use of GPS will
demand even greater vigilance, as off-course
deviations among different pilots and receivers will
be less. When operating near a VFR waypoint, use
whatever ATC services are available, even if outside
a class of airspace where communications are
required. Regardless of the class of airspace, monitor
the available ATC frequency closely for information
on other aircraft operating in the vicinity. It is also a
good idea to turn on your landing light(s) when
operating near a VFR waypoint to make your aircraft
more conspicuous to other pilots, especially when
visibility is reduced. See paragraph 2, VFR in
Congested Areas, in ENR 5.7, for more information.
18.4_General Requirements
18.4.1_Authorization to conduct any GPS operation
under IFR requires that:
18.4.1.1_GPS navigation equipment used must be
approved in accordance with the requirements
specified in TSO-C-129, or equivalent, and the
installation must be done in accordance with
Notice_8110.47 or 8110.48, or equivalent. Equipment
approved in accordance with TSO-C-115a does not
meet the requirements of TSO-C-129. VFR and
hand-held GPS systems are not authorized for IFR
navigation, instrument approaches, or as a principal
instrument flight reference. During IFR operations
they may be considered only an aid to situational
awareness.
18.4.1.2_Aircraft using GPS navigation equipment
under IFR must be equipped with an approved and
operational alternate means of navigation appropriate
to the flight. Active monitoring of alternative
navigation equipment is not required if the GPS
receiver uses RAIM for integrity monitoring. Active
monitoring of an alternate means of navigation is
AIP ENR 4.1-26
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required when the RAIM capability of the GPS
equipment is lost.
18.4.1.3_Procedures must be established for use in
the event that the loss of RAIM capability is predicted
to occur. In situations where this is encountered, the
flight must rely on other approved equipment, delay
departure, or cancel the flight.
18.4.1.4_The GPS operation must be conducted in
accordance with the FAA-approved aircraft flight
manual (AFM) or flight manual supplement. Flight
crew members must be thoroughly familiar with the
particular GPS equipment installed in the aircraft, the
receiver operation manual, and the AFM or flight
manual supplement. Unlike ILS and VOR, the basic
operation, receiver presentation to the pilot, and some
capabilities of the equipment can vary greatly. Due to
these differences, operation of different brands, or
even models of the same brand, of GPS receiver
under IFR should not be attempted without thorough
study of the operation of that particular receiver and
installation. Most receivers have a built-in simulator
mode which will allow the pilot to become familiar
with operation prior to attempting operation in the
aircraft. Using the equipment in flight under VFR
conditions prior to attempting IFR operation will
allow further familiarization.
18.4.1.5_Aircraft navigating by IFR approved GPS
are considered to be RNAV aircraft and have special
equipment suffixes. File the appropriate equipment
suffix in accordance with TBL ENR 4.1-4, on the
ATC flight plan. If GPS avionics become inoperative,
the pilot should advise ATC and amend the
equipment suffix.
18.4.1.6_Prior to any GPS IFR operation, the pilot
must review appropriate NOTAMs and aeronautical
information. (See GPS NOTAMs/Aeronautical
Information.)
18.4.1.7_Air carrier and commercial operators must
meet the appropriate provisions of their approved
operations specifications.
18.5_Use of GPS for IFR Oceanic, Domestic
En_Route, and Terminal Area Operations
18.5.1_GPS IFR operations in oceanic areas can be
conducted as soon as the proper avionics systems are
installed, provided all general requirements are met.
A GPS installation with TSO-C-129 authorization in
class A1, A2, B1, B2, C1, or C2 may be used to
replace one of the other approved means of
long-range navigation, such as dual INS. (See
TBL ENR 4.1-4 and TBL ENR 4.1-5.) A single
GPS installation with these classes of equipment
which provide RAIM for integrity monitoring may
also be used on short oceanic routes which have only
required one means of long-range navigation.
18.5.2_GPS domestic en route and terminal IFR
operations can be conducted as soon as proper
avionics systems are installed, provided all general
requirements are met. The avionics necessary to
receive all of the ground-based facilities appropriate
for the route to the destination airport and any
required alternate airport must be installed and
operational. Ground-based facilities necessary for
these routes must also be operational.
18.5.2.1_GPS en route IFR RNAV operations may be
conducted in Alaska outside the operational service
volume of ground-based navigation aids when a
TSO-C145a or TSO-C146a GPS/WAAS system is
installed and operating. Ground-based navigation
equipment is not required to be installed and
operating for en route IFR RNAV operations when
using GPS WAAS navigation systems. All operators
should ensure that an alternate means of navigation is
available in the unlikely event the GPS WAAS
navigation system becomes inoperative.
AIP ENR 4.1-27
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
TBL ENR 4.1-4
GPS IFR Equipment Classes/Categories
TSO-C129
Equipment
Class
RAIM
Int. Nav Sys.
to Prov.
RAIM Equiv.
Oceanic En Route Terminal
Nonprecision
Approach
Capable
Class A - GPS sensor and navigation capability.
A1 yes yes yes yes yes
A2 yes yes yes yes no
Class B - GPS sensor data to an integrated navigation system (i.e. FMS, multi-sensor navigation system, etc.).
B1 yes yes yes yes yes
B2 yes yes yes yes no
B3 yes yes yes yes yes
B4 yes yes yes yes no
Class C - GPS sensor data to an integrated navigation system (as in Class B) which provides enhanced guidance to an
autopilot, or flight director, to reduce flight tech. errors. Limited to 14 CFR Part 121 or equivalent criteria.
C1 yes yes yes yes yes
C2 yes yes yes yes no
C3 yes yes yes yes yes
C4 yes yes yes yes no
TBL ENR 4.1-5
GPS Approval Required/Authorized Use
Equipment
Type1
Installation
Approval
Required
Operational
Approval
Required
IFR
En Route2
IFR
Terminal2
IFR
Approach3
Oceanic
Remote
In Lieu of
ADF and/or
DME3
Hand held4 X5
VFR Panel
Mount4
X
IFR En Route
and Terminal
X X X X X
IFR Oceanic/
Remote
X X X X X X
IFR En Route,
Terminal, and
Approach
X X X X X X
NOTE-
1
To determine equipment approvals and limitations, refer to the AFM, AFM supplements, or pilot guides.
2
Requires verification of data for correctness if database is expired.
3
Requires current database.
4
VFR and hand-held GPS systems are not authorized for IFR navigation, instrument approaches, or as a primary instrument
flight reference. During IFR operations they may be considered only an aid to situational awareness.
5
Hand-held receivers require no approval. However, any aircraft modification to support the hand-held receiver;
i.e.,_installation of an external antenna or a permanent mounting bracket, does require approval.
AIP ENR 4.1-28
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
18.5.3_The GPS Approach Overlay Program is an
authorization for pilots to use GPS avionics under
IFR for flying designated nonprecision instrument
approach procedures, except LOC, LDA, and
simplified directional facility (SDF) procedures.
These procedures are now identified by the name of
the procedure and _or GPS" (e.g., VOR/DME or GPS
RWY_15). Other previous types of overlays have
either been converted to this format or replaced with
stand-alone procedures. Only approaches contained
in the current onboard navigation database are
authorized. The navigation database may contain
information about nonoverlay approach procedures
that is intended to be used to enhance position
orientation, generally by providing a map, while
flying these approaches using conventional
NAVAIDs. This approach information should not be
confused with a GPS overlay approach (see the
receiver operating manual, AFM, or AFM
Supplement for details on how to identify these
approaches in the navigation database).
NOTE-
Overlay approaches are predicated upon the design
criteria of the ground-based NAVAID used as the basis of
the approach. As such, they do not adhere to the design
criteria described in Section ENR 1.5, paragraph 12.10,
Area Navigation (RNAV) Instrument Approach Charts, for
stand-alone GPS approaches.
18.5.4_GPS IFR approach operations can be
conducted as soon as proper avionics systems are
installed and the following requirements are met:
18.5.4.1_The authorization to use GPS to fly
instrument approaches is limited to U.S. airspace.
18.5.4.2_The use of GPS in any other airspace must
be expressly authorized by the FAA Administrator.
18.5.4.3_GPS instrument approach operations outside the U.S. must be authorized by the appropriate
sovereign authority.
18.6_Equipment and Database Requirements
18.6.1_Authorization to fly approaches under IFR
using GPS avionics systems requires that:
18.6.1.1_A pilot use GPS avionics with TSO-C-129,
or equivalent, authorization in class A1, B1, B3, C1,
or C3.
18.6.1.2_All approach procedures to be flown must
be retrievable from the current airborne navigation
database supplied by the TSO-C-129 equipment
manufacturer or other FAA approved source.
18.6.1.3_Prior to using a procedure or waypoint
retrieved from the airborne navigation database, the
pilot should verify the validity of the database. This
verification should include the following preflight
and in-flight steps:
a)_Preflight:
1)_Determine the date of database issuance, and
verify that the date/time of proposed use is before the
expiration date/time.
2)_Verify that the database provider has not
published a notice limiting the use of the specific
waypoint or procedure.
b)_Inflight:
1)_Determine that the waypoints and transition
names coincide with names found on the procedure
chart. Do not use waypoints, which do not exactly
match the spelling shown on published procedure
charts.
2)_Determine that the waypoints are generally
logical in location, in the correct order, and that their
orientation to each other is as found on the procedure
chart, both laterally and vertically.
NOTE-
There is no specific requirement to check each waypoint
latitude and longitude, type of waypoint and/or altitude
constraint, only the general relationship of waypoints in
the procedure, or the logic of an individual waypoint’s
location.
3)_If the cursory check of procedure logic or
individual waypoint location, specified in 2) above,
indicates a potential error, do not use the retrieved
procedure or waypoint until a verification of latitude
and longitude, waypoint type, and altitude constraints
indicate full conformity with the published data.
AIP ENR 4.1-29
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
18.7_GPS Approach Procedures
18.7.1_As the production of stand-alone GPS
approaches has progressed, many of the original
overlay approaches have been replaced with
stand-alone procedures specifically designed for use
by GPS systems. The title of the remaining GPS
overlay procedures has been revised on the approach
chart to _or GPS" (e.g., VOR or GPS RWY 24).
Therefore, all the approaches that can be used by GPS
now contain _GPS" in the title (e.g., _VOR or GPS
RWY 24," _GPS RWY 24," or _RNAV (GPS)
RWY_24"). During these GPS approaches, underlying ground-based NAVAIDs are not required to be
operational and associated aircraft avionics need not
be installed, operational, turned on or monitored
(monitoring of the underlying approach is suggested
when equipment is available and functional).
Existing overlay approaches may be requested using
the GPS title, such as _GPS RWY 24" for the VOR or
GPS RWY_24.
NOTE-
Any required alternate airport must have an approved
instrument approach procedure other than GPS that is
anticipated to be operational and available at the
estimated time of arrival, and which the aircraft is
equipped to fly.
18.8_GPS NOTAMs/Aeronautical Information
18.8.1_GPS satellite outages are issued as GPS
NOTAMs both domestically and internationally.
However, the effect of an outage on the intended
operation cannot be determined unless the pilot has a
RAIM availability prediction program which allows
excluding a satellite which is predicted to be out of
service based on the NOTAM information.
18.8.2_The term UNRELIABLE is used in conjunction with GPS NOTAMs. The term UNRELIABLE
is an advisory to pilots indicating the expected level
of service may not be available. GPS operation may
be NOTAMed UNRELIABLE due to testing or
anomalies. Air Traffic Control will advise pilots
requesting a GPS or RNAV (GPS) approach of GPS
UNRELIABLE for:
18.8.2.1_NOTAMs not contained in the ATIS
broadcast.
18.8.2.2_Pilot reports of GPS anomalies received
within the preceding 15 minutes.
18.8.3_Civilian pilots may obtain GPS RAIM
availability information for nonprecision approach
procedures by specifically requesting GPS aeronautical information from an Automated Flight Service
Station during preflight briefings. GPS RAIM
aeronautical information can be obtained for a period
of 3 hours (ETA hour and 1 hour before to 1 hour after
the ETA hour) or a 24-hour time frame at a particular
airport. FAA briefers will provide RAIM information
for a period of 1 hour before to 1 hour after the ETA,
unless a specific time frame is requested by the pilot.
If flying a published GPS departure, a RAIM
prediction should also be requested for the departure
airport.
18.8.4_The military provides airfield specific GPS
RAIM NOTAMs for nonprecision approach procedures at military airfields. The RAIM outages are
issued as M-series NOTAMs and may be obtained for
up to 24 hours from the time of request.
18.8.5_Receiver manufacturers and/or database
suppliers may supply _NOTAM" type information
concerning database errors. Pilots should check these
sources, when available, to ensure that they have the
most current information concerning their electronic
database.
18.9_Receiver Autonomous Integrity Monitoring
(RAIM)
18.9.1_RAIM outages may occur due to an
insufficient number of satellites or due to unsuitable
satellite geometry which causes the error in the
position solution to become too large. Loss of satellite
reception and RAIM warnings may occur due to
aircraft dynamics (changes in pitch or bank angle).
Antenna location on the aircraft, satellite position
relative to the horizon, and aircraft attitude may affect
reception of one or more satellites. Since the relative
positions of the satellites are constantly changing,
prior experience with the airport does not guarantee
reception at all times, and RAIM availability should
always be checked.
18.9.2_If RAIM is not available, another type of
navigation and approach system must be used,
another destination selected, or the trip delayed until
RAIM is predicted to be available on arrival. On
longer flights, pilots should consider rechecking the
RAIM prediction for the destination during the flight.
This may provide early indications that an
unscheduled satellite outage has occurred since
takeoff.
AIP ENR 4.1-30
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
18.9.3_If a RAIM failure/status annunciation
occurs prior to the final approach waypoint
(FAWP), the approach should not be completed
since GPS may no longer provide the required
accuracy. The receiver performs a RAIM prediction
by 2 NM prior to the FAWP to ensure that RAIM is
available at the FAWP as a condition for entering the
approach mode. The pilot should ensure that the
receiver has sequenced from _Armed" to
_Approach" prior to the FAWP (normally occurs 2
NM prior). Failure to sequence may be an indication
of the detection of a satellite anomaly, failure to arm
the receiver (if required), or other problems which
preclude completing the approach.
18.9.4_If the receiver does not sequence into the
approach mode or a RAIM failure/status annunciation occurs prior to the FAWP, the pilot should not
descend to MDA, but should proceed to the missed
approach waypoint (MAWP) via the FAWP, perform
a missed approach, and contact ATC as soon as
practical. Refer to the receiver operating manual for
specific indications and instructions associated with
loss of RAIM prior to the FAF.
18.9.5_If a RAIM failure occurs after the FAWP, the
receiver is allowed to continue operating without an
annunciation for up to 5 minutes to allow completion
of the approach (see receiver operating manual). If
the RAIM flag/status annunciation appears after
the FAWP, the missed approach should be
executed immediately.
18.10_Waypoints
18.10.1_GPS approaches make use of both fly-over
and fly-by waypoints. Fly-by waypoints are used
when an aircraft should begin a turn to the next course
prior to reaching the waypoint separating the
two_route segments. This is known as turn
anticipation and is compensated for in the airspace
and terrain clearances. Approach waypoints, except
for the MAWP and the missed approach holding
waypoint (MAHWP), are normally fly-by waypoints. Fly-over waypoints are used when the aircraft
must fly over the point prior to starting a turn. New
approach charts depict fly-over waypoints as a
circled waypoint symbol. Overlay approach charts
and some early stand alone GPS approach charts may
not reflect this convention.
18.10.2_Since GPS receivers are basically _To-To"
navigators, they must always be navigating to a
defined point. On overlay approaches, if no
pronounceable five-character name is published for
an approach waypoint or fix, it was given a database
identifier consisting of letters and numbers. These
points will appear in the list of waypoints in the
approach procedure database, but may not appear on
the approach chart. A point used for the purpose of
defining the navigation track for an airborne
computer system (i.e., GPS or FMS) is called a
Computer Navigation Fix (CNF). CNFs include
unnamed DME fixes, beginning and ending points of
DME arcs, and sensor final approach fixes (FAFs) on
some GPS overlay approaches. To aid in the approach
chart/database correlation process, the FAA has
begun a program to assign five-letter names to CNFs
and to chart CNFs on various FAA aeronautical
products. These CNFs are not to be used for any air
traffic control (ATC) application, such as holding for
which the fix has not already been assessed. CNFs
will be charted to distinguish them from conventional
reporting points, fixes, intersections, and waypoints.
The CNF name will be enclosed in parenthesis;
e.g.,_(MABEE), and the name will be placed next to
the CNF it defines. If the CNF is not at an existing
point defined by means such as crossing radials or
radial/DME, the point will be indicated by an _X."
The CNF name will not be used in filing a flight plan
or in aircraft/ATC communications. Use current
phraseology; e.g., facility name, radial, distance, to
describe these fixes.
18.10.3_Unnamed waypoints in the database will be
uniquely identified for each airport but may be
repeated for another airport (e.g., RW36 will be used
at each airport with a runway 36 but will be at the
same location for all approaches at a given airport).
18.10.4_The runway threshold waypoint, which is
normally the MAWP, may have a five letter identifier
(e.g., SNEEZ) or be coded as RW## (e.g., RW36,
RW36L). Those thresholds which are coded as five
letter identifiers are being changed to the RW##
designation. This may cause the approach chart and
database to differ until all changes are complete. The
runway threshold waypoint is also used as the center
of the MSA on most GPS approaches. MAWPs not
located at the threshold will have a five letter
identifier.
AIP ENR 4.1-31
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
18.11_Position Orientation
18.11.1_As with most RNAV systems, pilots should
pay particular attention to position orientation while
using GPS. Distance and track information are
provided to the next active waypoint, not to a fixed
navigation aid. Receivers may sequence when the
pilot is not flying along an active route, such as when
being vectored or deviating for weather, due to the
proximity to another waypoint in the route. This can
be prevented by placing the receiver in the
nonsequencing mode. When the receiver is in the
nonsequencing mode, bearing and distance are
provided to the selected waypoint, and the receiver
will not sequence to the next waypoint in the route
until placed back in the auto sequence mode or the
pilot selects a different waypoint. On overlay
approaches, the pilot may have to compute the along
track distance to stepdown fixes and other points due
to the receiver showing along track distance to the
next waypoint rather than DME to the VOR or ILS
ground station.
18.12_Conventional Versus GPS Navigation Data
18.12.1_There may be slight differences between the
course information portrayed on navigational charts
and a GPS navigation display when flying authorized
GPS instrument procedures or along an airway. All
magnetic tracks defined by any conventional
navigation aids are determined by the application of
the station magnetic variation. In contrast, GPS
RNAV systems may use an algorithm, which applies
the local magnetic variation and may produce small
differences in the displayed course. However, both
methods of navigation should produce the same
desired ground track when using approved, IFR
navigation system. Should significant differences
between the approach chart and the GPS avionics’
application of the navigation database arise, the
published approach chart, supplemented by
NOTAMs, holds precedence.
18.12.2_Due to the GPS avionics’ computation of
great circle courses, and the variations in magnetic
variation, the bearing to the next waypoint and the
course from the last waypoint (if available) may not
be exactly 180 _ apart when long distances are
involved. Variations in distances will occur since
GPS distance-to-waypoint values are along-track
distances (ATD) computed to the next waypoint and
the DME values published on underlying procedures
are slant-range distances measured to the station.
This difference increases with aircraft altitude and
proximity to the NAVAID
18.13_Departures and Instrument Departure
Procedures (DPs)
18.13.1_The GPS receiver must be set to terminal
(±1 NM) course deviation indicator (CDI) sensitivity and the navigation routes contained in the
database in order to fly published IFR charted
departures and DPs. Terminal RAIM should be
automatically provided by the receiver. (Terminal
RAIM for departure may not be available unless the
waypoints are part of the active flight plan rather than
proceeding direct to the first destination.) Certain
segments of a DP may require some manual
intervention by the pilot, especially when radar
vectored to a course or required to intercept a specific
course to a waypoint. The database may not contain
all of the transitions or departures from all runways
and some GPS receivers do not contain DPs in the
database. It is necessary that helicopter procedures be
flown at 70 knots or less since helicopter departure
procedures and missed approaches use a 20:1
obstacle clearance surface (OCS), which is double the
fixed-wing OCS, and turning areas are based on this
speed as well.
18.14_Flying GPS Approaches
18.14.1_Determining which area of the TAA the
aircraft will enter when flying a _T" with a TAA must
be accomplished using the bearing and distance to the
IF(IAF). This is most critical when entering the TAA
in the vicinity of the extended runway centerline and
determining whether you will be entering the right or
left base area. Once inside the TAA, all sectors and
stepdowns are based on the bearing and distance to
the IAF for that area, which the aircraft should be
proceeding direct to at that time, unless on vectors.
(See FIG ENR 1.5-14 and FIG ENR 1.5-15.)
18.14.2_Pilots should fly the full approach from an
Initial Approach Waypoint (IAWP) or feeder fix
unless specifically cleared otherwise. Randomly
joining an approach at an intermediate fix does not
assure terrain clearance.
18.14.3_When an approach has been loaded in the
flight plan, GPS receivers will give an _arm"
annunciation 30 NM straight line distance from the
airport/heliport reference point. Pilots should arm the
approach mode at this time, if it has not already been
armed (some receivers arm automatically). Without
arming, the receiver will not change from en route
AIP ENR 4.1-32
United States of America 15 MAR 07
Federal Aviation Administration
Nineteenth Edition
CDI and RAIM sensitivity of ±5 NM either side of
centerline to ±1 NM terminal sensitivity. Where the
IAWP is inside this 30 mile point, a CDI sensitivity
change will occur once the approach mode is armed
and the aircraft is inside 30 NM. Where the IAWP is
beyond 30 NM from the airport/heliport reference
point, CDI sensitivity will not change until the
aircraft is within 30 miles of the airport/heliport
reference point even if the approach is armed earlier.
Feeder route obstacle clearance is predicated on the
receiver being in terminal (±1 NM) CDI sensitivity
and RAIM within 30 NM of the airport/heliport
reference point, therefore, the receiver should always
be armed (if required) not later than the 30 NM
annunciation.
18.14.4_The pilot must be aware of what bank
angle/turn rate the particular receiver uses to compute
turn anticipation, and whether wind and airspeed are
included in the receiver’s calculations. This information should be in the receiver operating manual. Over
or under banking the turn onto the final approach
course may significantly delay getting on course and
may result in high descent rates to achieve the next
segment altitude.
18.14.5_When within 2 NM of the FAWP with the
approach mode armed, the approach mode will
switch to active, which results in RAIM changing to
approach sensitivity and a change in CDI sensitivity.
Beginning 2 NM prior to the FAWP, the full scale CDI
sensitivity will smoothly change from ±1 NM, to
±0.3 NM at the FAWP. As sensitivity changes from
±1 NM to ±0.3 NM approaching the FAWP, with the
CDI not centered, the corresponding increase in CDI
displacement may give the impression that the
aircraft is moving further away from the intended
course even though it is on an acceptable intercept
heading. Referencing the digital track displacement
information (cross track error), if it is available in the
approach mode, may help the pilot remain position
oriented in this situation. Being established on the
final approach course prior to the beginning of the
sensitivity change at 2 NM will help prevent
problems in interpreting the CDI display during ramp
down. Therefore, requesting or accepting vectors
which will cause the aircraft to intercept the final
approach course within 2 NM of the FAWP is not
recommended.
18.14.6_When receiving vectors to final, most
receiver operating manuals suggest placing the
receiver in the nonsequencing mode on the FAWP
and manually setting the course. This provides an
extended final approach course in cases where the
aircraft is vectored onto the final approach course
outside of any existing segment which is aligned with
the runway. Assigned altitudes must be maintained
until established on a published segment of the
approach. Required altitudes at waypoints outside the
FAWP or stepdown fixes must be considered.
Calculating the distance to the FAWP may be
required in order to descend at the proper location.
18.14.7_Overriding an automatically selected sensitivity during an approach will cancel the approach
mode annunciation. If the approach mode is not
armed by 2 NM prior to the FAWP, the approach
mode will not become active at 2 NM prior to the
FAWP, and the equipment will flag. In these
conditions, the RAIM and CDI sensitivity will not
ramp down, and the pilot should not descend to MDA,
but fly to the MAWP and execute a missed approach.
The approach active annunciator and/or the receiver
should be checked to ensure the approach mode is
active prior to the FAWP.
18.14.8_Do not attempt to fly an approach unless the
procedure is contained in the current, on-board
navigation database and identified as _GPS" on the
approach chart. The navigation database may contain
information about nonoverlay approach procedures
that is intended to be used to enhance position
orientation, generally by providing a map, while
flying these approaches using conventional NA-
VAIDs. This approach information should not be
confused with a GPS overlay approach (see the
receiver operating manual, AFM, or AFM Supplement for details on how to identify these procedures
in the navigation database). Flying point to point on
the approach does not assure compliance with the
published approach procedure. The proper RAIM
sensitivity will not be available and the CDI
sensitivity will not automatically change to
±0.3_NM. Manually setting CDI sensitivity does not
automatically change the RAIM sensitivity on some
receivers. Some existing nonprecision approach
procedures cannot be coded for use with GPS and will
not be available as overlays.
18.14.9_Pilots should pay particular attention to the
exact operation of their GPS receivers for performing
holding patterns, and, in the case of overlay
approaches, operations such as procedure turns.
These procedures may require manual intervention
AIP ENR 4.1-33
United States of America 15 MAR 07
Federal Aviation Administration Nineteenth Edition
by the pilot to stop the sequencing of waypoints by the
receiver and to resume automatic GPS navigation
sequencing once the maneuver is complete. The same
waypoint may appear in the route of flight more than
once consecutively (e.g., IAWP, FAWP, MAHWP on
a procedure turn). Care must be exercised to ensure
that the receiver is sequenced to the appropriate
waypoint for the segment of the procedure being
flown, especially if one or more fly-overs are skipped
(e.g., FAWP rather than IAWP if the procedure turn
is not flown). The pilot may have to sequence past one
or more fly-overs of the same waypoint in order to
start GPS automatic sequencing at the proper place in
the sequence of waypoints.
18.14.10_Incorrect inputs into the GPS receiver are
especially critical during approaches. In some cases,
an incorrect entry can cause the receiver to leave the
approach mode.
18.14.11_A fix on an overlay approach identified by
a DME fix will not be in the waypoint sequence on the
GPS receiver unless there is a published name
assigned to it. When a name is assigned, the along
track to the waypoint may be zero rather than the
DME stated on the approach chart. The pilot should
be alert for this on any overlay procedure where the
original approach used DME.
18.14.12_If a visual descent point (VDP) is
published, it will not be included in the sequence of
waypoints. Pilots are expected to use normal piloting
techniques for beginning the visual descent, such as
ATD.
18.14.13_Unnamed stepdown fixes in the final
approach segment will not be coded in the waypoint
sequence of the aircraft’s navigation database and
must be identified using ATD. Stepdown fixes in the
final approach segment of RNAV (GPS) approaches
are being named, in addition to being identified by
ATD. However, since most GPS avionics do not
accommodate waypoints between the FAF and MAP,
even when the waypoint is named, the waypoints for
these stepdown fixes may not appear in the sequence
of waypoints in the navigation database. Pilots must
continue to identify these stepdown fixes using ATD.
18.15_Missed Approach
18.15.1_A GPS missed approach requires pilot
action to sequence the receiver past the MAWP to the
missed approach portion of the procedure. The pilot
must be thoroughly familiar with the activation
procedure for the particular GPS receiver installed in
the aircraft and must initiate appropriate action
after the MAWP. Activating the missed approach
prior to the MAWP will cause CDI sensitivity to
immediately change to terminal (±1 NM) sensitivity
and the receiver will continue to navigate to the
MAWP. The receiver will not sequence past the
MAWP. Turns should not begin prior to the MAWP.
If the missed approach is not activated, the GPS
receiver will display an extension of the inbound final
approach course and the ATD will increase from the
MAWP until it is manually sequenced after crossing
the MAWP.
18.15.2_Missed approach routings in which the first
track is via a course rather than direct to the next
waypoint require additional action by the pilot to
set the course. Being familiar with all of the inputs
required is especially critical during this phase of
flight.
18.16_GPS Familiarization_
18.16.1_Pilots should practice GPS approaches
under visual meteorological conditions (VMC) until
thoroughly proficient with all aspects of their
equipment (receiver and installation) prior to
attempting flight by IFR in instrument meteorological conditions (IMC). Some of the areas which the
pilot should practice are:
18.16.1.1_Utilizing the receiver autonomous
integrity monitoring (RAIM) prediction function.
18.16.1.2_Inserting a DP into the flight plan,
including setting terminal CDI sensitivity, if required,
and the conditions under which terminal RAIM is
available for departure. (Some receivers are not DP or
STAR capable.)
18.16.1.3_Programming the destination airport.
18.16.1.4_Programming and flying the overlay
approaches (especially procedure turns and arcs).
18.16.1.5_Changing to another approach after
selecting an approach.
18.16.1.6_Programming and flying _direct" missed
approaches.
18.16.1.7_Programming and flying _routed" missed
approaches.
18.16.1.8_Entering, flying, and exiting holding
patterns, particularly on overlay approaches with a
second waypoint in the holding pattern.
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18.16.1.9_Programming and flying a _route" from a
holding pattern.
18.16.1.10_Programming and flying an approach
with radar vectors to the intermediate segment.
18.16.1.11_Indication of the actions required for
RAIM failure both before and after the FAWP.
18.16.1.12_Programming a radial and distance from
a VOR (often used in departure instructions).
19. Wide Area Augmentation System
(WAAS)
19.1_General
19.1.1_The FAA developed the Wide Area Augmentation System (WAAS) to improve the accuracy,
integrity and availability of GPS signals. WAAS will
allow GPS to be used, as the aviation navigation
system, from takeoff through Category I precision
approach when it is complete. WAAS is a critical
component of the FAA’s strategic objective for a
seamless satellite navigation system for civil
aviation, improving capacity and safety.
19.1.2_The International Civil Aviation Organization (ICAO) has defined Standards and
Recommended Practices (SARPs) for satellite-based
augmentation systems (SBAS) such as WAAS. Japan
and Europe are building similar systems that are
planned to be interoperable with WAAS: EGNOS,
the European Geostationary Navigation Overlay
System, and MSAS, the Japan Multifunctional
Transport Satellite (MTSAT) Satellite-based Augmentation System. The merging of these systems will
create a worldwide seamless navigation capability
similar to GPS but with greater accuracy, availability
and integrity.
19.1.3_Unlike traditional ground-based navigation
aids, WAAS will cover a more extensive service area.
Precisely surveyed wide-area ground reference
stations (WRS) are linked to form the U.S. WAAS
network. Signals from the GPS satellites are
monitored by these WRSs to determine satellite clock
and ephemeris corrections and to model the
propagation effects of the ionosphere. Each station in
the network relays the data to a wide-area master
station (WMS) where the correction information is
computed. A correction message is prepared and
uplinked to a geostationary satellite (GEO) via a
ground uplink station (GUS). The message is then
broadcast on the same frequency as GPS (L1,
1575.42 MHz) to WAAS receivers within the
broadcast coverage area of the WAAS GEO.
19.1.4_In addition to providing the correction signal,
the WAAS GEO provides an additional pseudorange
measurement to the aircraft receiver, improving the
availability of GPS by providing, in effect, an
additional GPS satellite in view. The integrity of GPS
is improved through real-time monitoring, and the
accuracy is improved by providing differential
corrections to reduce errors. The performance
improvement is sufficient to enable approach
procedures with GPS/WAAS glide paths (vertical
guidance).
19.1.5_The FAA has completed installation of
25_WRSs, 2 WMSs, 4 GUSs, and the required
terrestrial communications to support the WAAS
network. Prior to the commissioning of the WAAS for
public use, the FAA has been conducting a series of
test and validation activities. Enhancements to the
initial phase of WAAS will include additional master
and reference stations, communication satellites, and
transmission frequencies as needed.
19.1.6_GNSS navigation, including GPS and
WAAS, is referenced to the WGS-84 coordinate
system. It should only be used where the Aeronautical
Information Publications (including electronic data
and aeronautical charts) conform to WGS-84 or
equivalent. Other countries civil aviation authorities
may impose additional limitations on the use of their
SBAS systems.
19.2_Instrument Approach Capabilities
19.2.1_A new class of approach procedures which
provide vertical guidance, but which do not meet the
ICAO Annex 10 requirements for precision
approaches has been developed to support satellite
navigation use for aviation applications worldwide.
These new procedures called Approach with Vertical
Guidance (APV), are defined in ICAO Annex 6, and
include approaches such as the LNAV/VNAV
procedures presently being flown with barometric
vertical navigation (Baro-VNAV). These approaches
provide vertical guidance, but do not meet the more
stringent standards of a precision approach. Properly
certified WAAS receivers will be able to fly these
LNAV/VNAV procedures using a WAAS electronic
glide path, which eliminates the errors that can be
introduced by using Barometric altimetery.
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19.2.2 A new type of APV approach procedure, in
addition to LNAV/VNAV, is being implemented to
take advantage of the high accuracy guidance and
increased integrity provided by WAAS. This WAAS
generated angular guidance allows the use of the
same TERPS approach criteria used for ILS
approaches. The resulting approach procedure
minima, titled LPV (localizer performance with
vertical guidance), may have a decision altitude as
low as 200 feet height above touchdown with
visibility minimums as low as 1
/2 mile, when the
terrain and airport infrastructure support the lowest
minima. LPV minima is published on the RNAV
(GPS) approach charts (see paragraph 12, Instrument
Approach Procedure Charts).
19.2.3 A new nonprecision WAAS approach, called
Localizer Performance (LP) is being added in
locations where the terrain or obstructions do not
allow publication of vertically guided LPV
procedures. This new approach takes advantage of
the angular lateral guidance and smaller position
errors provided by WAAS to provide a lateral only
procedure similar to an ILS Localizer. LP procedures
may provide lower minima than a LNAV procedure
due to the narrower obstacle clearance surface.
NOTE-
WAAS receivers certified prior to TSO C-145b and TSO
C-146b, even if they have LPV capability, do not contain
LP capability unless the receiver has been upgraded.
Receivers capable of flying LP procedures must contain a
statement in the Flight Manual Supplement or Approved
Supplemental Flight Manual stating that the receiver has
LP capability, as well as the capability for the other WAAS
and GPS approach procedure types.
19.2.4 WAAS provides a level of service that
supports all phases of flight, including LNAV, LP,
LNAV/VNAV and LPV approaches, within system
coverage. Some locations close to the edge of the
coverage may have a lower availability of vertical
guidance.
19.3 General Requirements
19.3.1 WAAS avionics must be certified in accordance with Technical Standard Order (TSO)
C-145A, Airborne Navigation Sensors Using the
(GPS) Augmented by the Wide Area Augmentation
System (WAAS); or TSO-146A, Stand-Alone
Airborne Navigation Equipment Using the Global
Positioning System (GPS) Augmented by the Wide
Area Augmentation System (WAAS), and installed in
accordance with Advisory Circular (AC) 20-130A,
Airworthiness Approval of Navigation or Flight
Management Systems Integrating Multiple Navigation Sensors, or AC 20-138A, Airworthiness
Approval of Global Positioning System (GPS)
Navigation Equipment for Use as a VFR and IFR
Navigation System.
19.3.2 GPS/WAAS operation must be conducted in
accordance with the FAA-approved aircraft flight
manual (AFM) and flight manual supplements. Flight
manual supplements will state the level of approach
procedure that the receiver supports. IFR approved
WAAS receivers support all GPS only operations as
long as lateral capability at the appropriate level is
functional. WAAS monitors both GPS and WAAS
satellites and provides integrity.
19.3.3 GPS/WAAS equipment is inherently capable
of supporting oceanic and remote operations if the
operator obtains a fault detection and exclusion
(FDE) prediction program.
19.3.4 Air carrier and commercial operators must
meet the appropriate provisions of their approved
operations specifications.
19.3.5 Prior to GPS/WAAS IFR operation, the pilot
must review appropriate Notices to Airmen
(NOTAMs) and aeronautical information. This
information is available on request from an
Automated Flight Service Station. The FAA will
provide NOTAMs to advise pilots of the status of the
WAAS and level of service available.
19.3.5.1 The term UNRELIABLE is used in
conjunction with GPS and WAAS NOTAMs. The
term UNRELIABLE is an advisory to pilots
indicating the expected level of WAAS service
(LNAV/VNAV, LPV) may not be available;
e.g., !BOS BOS WAAS LPV AND LNAV/VNAV
MNM UNREL WEF 0305231700 -0305231815.
WAAS UNRELIABLE NOTAMs are predictive in
nature and published for flight planning purposes.
Upon commencing an approach at locations
NOTAMed WAAS UNRELIABLE, if the WAAS
avionics indicate LNAV/VNAV or LPV service is
available, then vertical guidance may be used to
complete the approach using the displayed level of
service. Should an outage occur during the approach,
reversion to LNAV minima may be required.
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a) Area-wide WAAS UNAVAILABLE NOTAMs
indicate loss or malfunction of the WAAS system. In
flight, Air Traffic Control will advise pilots
requesting a GPS or RNAV (GPS) approach of
WAAS UNAVAILABLE NOTAMs if not contained
in the ATIS broadcast.
b) Site-specific WAAS UNRELIABLE
NOTAMs indicate an expected level of service,
e.g., LNAV/VNAV or LPV may not be available.
Pilots must request site-specific WAAS NOTAMs
during flight planning. In flight, Air Traffic Control
will not advise pilots of WAAS UNRELIABLE
NOTAMs.
c) When the approach chart is annotated with the
symbol, site-specific WAAS UNRELIABLE
NOTAMs or Air Traffic advisories are not provided
for outages in WAAS LNAV/VNAV and LPV vertical
service. Vertical outages may occur daily at these
locations due to being close to the edge of WAAS
system coverage. Use LNAV minima for flight
planning at these locations, whether as a destination
or alternate. For flight operations at these locations,
when the WAAS avionics indicate that LNAV/VNAV
or LPV service is available, then the vertical guidance
may be used to complete the approach using the
displayed level of service. Should an outage occur
during the procedure, reversion to LNAV minima
may be required.
NOTE-
Area-wide WAAS UNAVAILABLE NOTAMs apply to all
airports in the WAAS UNAVAILABLE area designated in
the NOTAM, including approaches at airports where an
approach chart is annotated with the symbol.
19.3.6 GPS/WAAS was developed to be used within
SBAS GEO coverage (WAAS or other interoperable
system) without the need for other radio navigation
equipment appropriate to the route of flight to be
flown. Outside the SBAS coverage or in the event of
a WAAS failure, GPS/WAAS equipment reverts to
GPS-only operation and satisfies the requirements
for basic GPS equipment.
19.3.7 Unlike TSO-C129 avionics, which were
certified as a supplement to other means of
navigation, WAAS avionics are evaluated without
reliance on other navigation systems. As such,
installation of WAAS avionics does not require the
aircraft to have other equipment appropriate to the
route to be flown.
19.3.7.1 Pilots with WAAS receivers may flight plan
to use any instrument approach procedure authorized
for use with their WAAS avionics as the planned
approach at a required alternate, with the following
restrictions. When using WAAS at an alternate
airport, flight planning must be based on flying the
RNAV (GPS) LNAV minima line, or minima on a
GPS approach procedure, or conventional approach
procedure with “or GPS” in the title. Code of Federal
Regulation (CFR) Part 91 nonprecision weather
requirements must be used for planning. Upon arrival
at an alternate, when the WAAS navigation system
indicates that LNAV/VNAV or LPV service is
available, then vertical guidance may be used to
complete the approach using the displayed level of
service. The FAA has begun removing the NA
(Alternate Minimums Not Authorized) symbol from
select RNAV (GPS) and GPS approach procedures so
they may be used by approach approved WAAS
receivers at alternate airports. Some approach
procedures will still require the NA for other
reasons, such as no weather reporting, so it cannot be
removed from all procedures. Since every procedure
must be individually evaluated, removal of the
NA from RNAV (GPS) and GPS procedures will
take some time.
19.4 Flying procedures with WAAS
19.4.1 WAAS receivers support all basic GPS
approach functions and provide additional capabilities. One of the major improvements is the ability to
generate glide path guidance, independent of ground
equipment or barometric aiding. This eliminates
several problems such as hot and cold temperature
effects, incorrect altimeter setting or lack of a local
altimeter source. It also allows approach procedures
to be built without the cost of installing ground
stations at each airport or runway. Some approach
certified receivers may only generate a glide path
with performance similar to Baro-VNAV and are
only approved to fly the LNAV/VNAV line of minima
on the RNAV (GPS) approach charts. Receivers with
additional capability (including faster update rates
and smaller integrity limits) are approved to fly the
LPV line of minima. The lateral integrity changes
dramatically from the 0.3 NM (556 meter) limit for
GPS, LNAV and LNAV/VNAV approach mode, to 40
meters for LPV. It also provides vertical integrity
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monitoring, which bounds the vertical error to 50
meters for LNAV/VNAV and LPVs with minima of
250’ or above, and bounds the vertical error to 35
meters for LPVs with minima below 250’.
19.4.2 When an approach procedure is selected and
active, the receiver will notify the pilot of the most
accurate level of service supported by the combination of the WAAS signal, the receiver, and the
selected approach, using the naming conventions on
the minima lines of the selected approach procedure.
For example, if an approach is published with LPV
minima and the receiver is only certified for
LNAV/VNAV, the equipment would indicate
“LNAV/VNAV available,” even though the WAAS
signal would support LPV. If flying an existing
LNAV/VNAV procedure with no LPV minima, the
receiver will notify the pilot “LNAV/VNAV
available,” even if the receiver is certified for LPV
and the signal supports LPV. If the signal does not
support vertical guidance on procedures with LPV
and/or LNAV/VNAV minima, the receiver annunciation will read “LNAV available.” On lateral only
procedures with LP and LNAV minima the receiver
will indicate “LP available” or “LNAV available”
based on the level of lateral service available. Once
the level of service notification has been given, the
receiver will operate in this mode for the duration of
the approach procedure, unless that level of service
becomes unavailable. The receiver cannot change
back to a more accurate level of service until the next
time an approach is activated.
NOTE-
Receivers do not “fail down” to lower levels of service
once the approach has been activated. If only the
vertical off flag appears, the pilot may elect to use the
LNAV minima if the rules under which the flight is
operating allow changing the type of approach being flown
after commencing the procedure. If the lateral integrity
limit is exceeded on an LP approach, a missed approach
will be necessary since there is no way to reset the lateral
alarm limit while the approach is active.
19.4.3 Another additional feature of WAAS receivers is the ability to exclude a bad GPS signal and
continue operating normally. This is normally
accomplished by the WAAS correction information.
Outside WAAS coverage or when WAAS is not
available, it is accomplished through a receiver
algorithm called FDE. In most cases this operation
will be invisible to the pilot since the receiver will
continue to operate with other available satellites
after excluding the “bad” signal. This capability
increases the reliability of navigation.
19.4.4 Both lateral and vertical scaling for the
LNAV/VNAV and LPV approach procedures are
different than the linear scaling of basic GPS. When
the complete published procedure is flown, +/-1 NM
linear scaling is provided until two (2) NM prior to the
FAF, where the sensitivity increases to be similar to
the angular scaling of an ILS. There are two
differences in the WAAS scaling and ILS: 1) on long
final approach segments, the initial scaling will be
+/-0.3 NM to achieve equivalent performance to
GPS (and better than ILS, which is less sensitive far
from the runway); 2) close to the runway threshold,
the scaling changes to linear instead of continuing to
become more sensitive. The width of the final
approach course is tailored so that the total width is
usually 700 feet at the runway threshold. Since the
origin point of the lateral splay for the angular portion
of the final is not fixed due to antenna placement like
localizer, the splay angle can remain fixed, making a
consistent width of final for aircraft being vectored
onto the final approach course on different length
runways. When the complete published procedure is
not flown, and instead the aircraft needs to capture the
extended final approach course similar to ILS, the
vector to final (VTF) mode is used. Under VTF the
scaling is linear at +/-1 NM until the point where the
ILS angular splay reaches a width of +/-1 NM
regardless of the distance from the FAWP.
19.4.5 The WAAS scaling is also different than GPS
TSO-C129 in the initial portion of the missed
approach. Two differences occur here. First, the
scaling abruptly changes from the approach scaling to
the missed approach scaling, at approximately the
departure end of the runway or when the pilot
requests missed approach guidance rather than
ramping as GPS does. Second, when the first leg of
the missed approach is a Track to Fix (TF) leg aligned
within 3 degrees of the inbound course, the receiver
will change to 0.3 NM linear sensitivity until the turn
initiation point for the first waypoint in the missed
approach procedure, at which time it will abruptly
change to terminal (+/-1 NM) sensitivity. This allows
the elimination of close in obstacles in the early part
of the missed approach that may cause the DA to be
raised.
19.4.6 A new method has been added for selecting
the final approach segment of an instrument
approach. Along with the current method used by
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most receivers using menus where the pilot selects the
airport, the runway, the specific approach procedure
and finally the IAF, there is also a channel number
selection method. The pilot enters a unique 5-digit
number provided on the approach chart, and the
receiver recalls the matching final approach segment
from the aircraft database. A list of information
including the available IAFs is displayed and the pilot
selects the appropriate IAF. The pilot should confirm
that the correct final approach segment was loaded by
cross checking the Approach ID, which is also
provided on the approach chart.
19.4.7 The Along-Track Distance (ATD) during the
final approach segment of an LNAV procedure (with
a minimum descent altitude) will be to the MAWP. On
LNAV/VNAV and LPV approaches to a decision
altitude, there is no missed approach waypoint so the
along-track distance is displayed to a point normally
located at the runway threshold. In most cases the
MAWP for the LNAV approach is located on the
runway threshold at the centerline, so these distances
will be the same. This distance will always vary
slightly from any ILS DME that may be present, since
the ILS DME is located further down the runway.
Initiation of the missed approach on the LNAV/
VNAV and LPV approaches is still based on reaching
the decision altitude without any of the items listed in
14 CFR Section 91.175 being visible, and must not be
delayed until the ATD reaches zero. The WAAS
receiver, unlike a GPS receiver, will automatically
sequence past the MAWP if the missed approach
procedure has been designed for RNAV. The pilot
may also select missed approach prior to the MAWP,
however, navigation will continue to the MAWP prior
to waypoint sequencing taking place.
