Global Positioning System (GPS) [page 2]
Instrument Landing System (ILS) --
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pages: 1: General & Requirements |
2: Usage & more Technical Info
- USE OF GPS FOR IFR OCEANIC, DOMESTIC ENROUTE, and TERMINAL
- 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 or dual Omega. A single GPS installation with these
classes of equipment which provides RAIM for integrity monitoring
may also be used on short oceanic routes which have only required
one means of long range navigation.
- GPS domestic enroute and terminal IFR operations can be conducted
as soon as the 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. The ground based
facilities necessary for these routes must also be operational.
- The GPS Approach Overlay Program permits pilots to use GPS
avionics under IFR for flying existing instrument approach procedures,
except localizer (LOC), localizer directional aid (LDA)
and simplified directional facility (SDF) procedures.
In the future, stand alone GPS approaches will be developed
and introduced into the NAS.
- GPS IFR approach operations can be conducted in accordance
with Phase I, Phase II or Phase III of the GPS Approach Overlay
Program, as appropriate, as soon as the proper avionics systems
are installed and the following requirements are met. This general
approval to use GPS to fly instrument approaches is limited
to U.S. airspace. The use of GPS in any other airspace must
be expressly authorized by the Administrator. GPS instrument
approach operations outside the United States must also be authorized
by the appropriate sovereign authority.
- EQUIPMENT AND DATABASE REQUIREMENTS
- Authorization to fly approaches under IFR using GPS avionics
systems require that:
- A pilot use GPS avionics with TSO C-129 authorization in
class A1, B1, B3, C1, or C3; and:
- The specific approach procedure to be flown must be retrievable
from the airborne navigation database associated with the
TSO C-129 equipment.
NOTE: GPS avionics systems installed and operated
in accordance with the AFS/AIR guidance dated July 20, 1992
are not approved for "overlay" program phase II or III.
- PHASES OF THE APPROACH OVERLAY PROGRAM
- Phase I - Under Phase I, GPS avionics can be used as the IFR
flight guidance system for approaches as long as the ground
based NAVAID(s) required by the published procedure is operational
and actively monitored while conducting the approach. Approach
clearances must be requested and approved using the published
title of the existing approach procedure such as "VOR Rwy 24".
- Phase II - Under Phase II, GPS avionics can be used as the
IFR flight guidance system for an approach without actively
monitoring the ground based NAVAID(s) which defines the approach.
However, the ground based NAVAID(s) must be operational. In
addition, the related avionics must be installed and operational
but need not be turned-on during the approach. Approaches must
be requested and approved using the published title of the existing
approach procedure such as "VOR Rwy 24".
- Phase III - Phase III begins when FAR Part 97 instrument approach
procedures are retitled "GPS or VOR Rwy 24". When this Phase
begins, ground based NAVAIDs are not required to be operational
and the associated aircraft avionics need not be installed,
operational, turned on or monitored. GPS approaches will be
requested and approved using the GPS title, such as "GPS Rwy
24". Pending FAA's publication of FAR Part 97 GPS approaches,
stand alone GPS approaches will be developed and authorized
on a case-by-case basis.
NOTE: In each Phase, any required alternate airport must
have an approved instrument approach procedure, other than GPS
or LORAN-C, which is anticipated to be operational and available
at the estimated time of arrival.
- GPS STANDARD INSTRUMENT APPROACH PROCEDURE (SIAP) DESIGN
- The objective of GPS procedures design is to supply seamless
navigation for all GPS equipped aircraft. GPS allows the most
direct routing to the initial approach waypoints for standardized
approaches at the maximum number of locations. The concepts
described in this section provide the pilot and the air traffic
controller with the most efficient method for routing traffic
to a particular destination.
- GPS approaches are designed utilizing a Basic "T" concept
with connecting terminal routes to the en route airway structure.
The Basic "T" design normally aligns the procedure on runway
centerline, with the missed approach point (MAP) located at
threshold, the final approach fix (FAF) 5 nautical miles (NM)
from threshold, and the intermediate fix (IF) 5NM from the FAF.
Two initial approach fixes (LAF) are located 4 or 5NM from the
IF (one on each side of the IF), normally at points 90 degrees
to the intermediate course. Missed approaches will normally
be predicated on courses and turn waypoints to the missed approach
holding fix. (See FIG 1-1-27)
- When terrain, airspace, or air traffic requirements preclude
use of standard Basic "T" approach construction, the flexibility
of GPS allows alternatives that exploit the benefits of seamless
navigation. Design possibilities include:
- Modification to the Basic "T" by eliminating one of the
IAFs, changing the length of the initial legs, or the angle
at which they intercept the intermediate segment.
- Use of an approach design which consists of intermediate
and final approach segments. This variation requires terminal
routes to an IAF at the IF; and, depending on the angle of
arrival at the fix, may require a holding pattern course reversal
to align the aircraft with the final approach course. (See
- Air Traffic radar vectors to a published segment of the
GPS approach procedure. Where terminal routes are not published
the approach will be annotated with the note: "RADAR REQUIRED."
- Recent applications of "free flight" concepts advance seamless
GPS procedure design philosophy, eliminate terminal routes,
and use the Basic "T" enhanced by the Terminal Arrival Area
(TAA). The objective of the TAA is to identify an area suitable
for GPS navigation from the en route structure direct to the
Basic "T." To the maximum extent possible, except where restricted
by limitations imposed by air traffic control, surrounding terrain
limitations, etc., this design is used for new or revised stand-alone
GPS SIAPs. The TAA is composed of three areas; the straight-in
area, the right base area, and the left base area. These areas
establish minimum terminal area IFR altitudes for procedural
- The straight-in area is semi-circular with a 30 l NM radius
arc beyond the top of the basic "T" centered on the IF. The
arc boundary of the straight-in area is equivalent to an IAF.
After crossing the boundary or when released by ATC within the
TAA, aircraft are expected to proceed on a direct course to
the IF. The left base and right base areas are bounded by the
top of the basic "T" and the extension of the intermediate segment
course, with 30 NM radius arcs centered on the IAF on each side
of the "T." (See FIG 1-1-29). The arc boundaries of the base
areas are equivalent to feeder fixes. After crossing the TAA
boundary from the en route phase of flight or when released
by ATC within the TAA, aircraft are expected to proceed on a
direct course to the appropriate corner IAF, depending on their
geographic position. Course reversals normally are not required
with a TAA because routing through the "T" IAFs provides flexibility
and standardization in maneuvering to the final approach course.
When circumstances require a course reversal it will be established
as a holding pattern in lieu of procedure turn at the IF which
will be designated as an IF (IAF).
- Normally, the TAA will be designed with only one minimum altitude.
There will be locations, especially in mountainous areas, where
it will be necessary to sectorize the TAA to provide for lower
altitudes prior to reaching the IAFs. Sectors may be delineated
using wedges of the circle and/or GPS nautical mile step-down
arcs. (See FIG 1-1-30). Where a step-down arc or sector is not
practical to establish lower altitudes at the IAFs, a holding
pattern course reversal will be provided. If certain parts of
the TAA encompass terrain or airspace which does not allow for
the establishment of an IAF within descent criteria, it may
be necessary to eliminate a portion of a quadrant (or even eliminate
the entire TAA). When a portion of the Basic "T" or TAA is unusable,
it may be necessary to establish a terminal route to the center
IF (IAF) for either a straight-in (NoPT) approach or a holding
pattern course reversal. Additionally, modifications to the
Basic "T;" e.g., leg length, or angle of turn to the intermediate
segment, may also be used when obstructions or airspace restrict
use of the basic approach design. (See FIG 1-1-31)
- Whenever a complete TAA is charted, the minimum safe altitude
(MSA) depiction found in the plan view of the approach will
be omitted as the TAA altitudes provide the minimum obstacle
clearances of the MSA.
- USE OF GPS FOR RECEIVER AUTONOMOUS INTEGRITY MONITORING (RAIM)
RAIM information is an on request item during preflight briefings.
GPS Receiver Autonomous Integrity Monitoring (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. 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.
Instrument Landing System (ILS) --
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