Aeronautical Information Manual (AIM), page 75

Index   74 -- Page 75 -- 76

the fixed-wing OCS, and turning areas are based on
this speed as well.

5. GPS Instrument Approach Procedures
(a) GPS overlay approaches are designated
non-precision instrument approach procedures that
pilots are authorized to fly using GPS avionics.
Localizer (LOC), localizer type directional aid
(LDA), and simplified directional facility (SDF)
procedures are not authorized. Overlay procedures
are identified by the "name of the procedure" and "or
GPS" (e.g., VOR/DME or GPS RWY 15) in the title.
Authorized procedures must be retrievable from a
current onboard navigation database. The naviga-
tion database may also enhance position orientation
by displaying a map containing information on
conventional NAVAID approaches. 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
Overlay approaches do not adhere to the design criteria
described in Paragraph 5-4-5m, Area Navigation (RNAV)
Instrument Approach Charts, for stand-alone GPS
approaches. Overlay approach criteria is based on the
design criteria used for ground-based NAVAID ap-
(b) Stand-alone approach procedures spe-
cifically designed for GPS systems have replaced
many of the original overlay approaches. All
approaches that contain "GPS" in the title (e.g.,
"VOR or GPS RWY 24," "GPS RWY 24," or
"RNAV (GPS) RWY 24") can be flown using GPS.
GPS-equipped aircraft do not need underlying
ground-based NAVAIDs or associated aircraft
avionics to fly the approach. Monitoring the
underlying approach with ground-based NAVAIDs is
suggested when able. Existing overlay approaches

may be requested using the GPS title; for example,

the VOR or GPS RWY 24 may be requested as "GPS

RWY 24." Some GPS procedures have a Terminal

Arrival Area (TAA) with an underlining RNAV


(c) For flight planning purposes,
TSO-C129() and TSO-C196()-equipped users
(GPS users) whose navigation systems have fault
detection and exclusion (FDE) capability, who
perform a preflight RAIM prediction for the

approach integrity at the airport where the RNAV
(GPS) approach will be flown, and have proper
knowledge and any required training and/or
approval to conduct a GPS-based IAP, may file
based on a GPS-based IAP at either the destination
or the alternate airport, but not at both locations. At
the alternate airport, pilots may plan for:
(1) Lateral navigation (LNAV) or circling
minimum descent altitude (MDA);

(2) LNAV/vertical navigation (LNAV/
VNAV) DA, if equipped with and using approved
barometric vertical navigation (baro-VNAV) equip-
(3) RNP 0.3 DA on an RNAV (RNP) IAP,
if they are specifically authorized users using
approved baro-VNAV equipment and the pilot has
verified required navigation performance (RNP)
availability through an approved prediction program.
(d) If the above conditions cannot be met, any
required alternate airport must have an approved
instrument approach procedure other than GPS-
based that is anticipated to be operational and
available at the estimated time of arrival, and which
the aircraft is equipped to fly.

(e) Procedures for Accomplishing GPS
(1) An RNAV (GPS) procedure may be
associated with a Terminal Arrival Area (TAA). The
basic design of the RNAV procedure is the "T" design
or a modification of the "T" (See Paragraph 5-4-5d,
Terminal Arrival Area (TAA), for complete informa-
(2) Pilots cleared by ATC for an RNAV
(GPS) approach should fly the full approach from an
Initial Approach Waypoint (IAWP) or feeder fix.
Randomly joining an approach at an intermediate fix
does not assure terrain clearance.

(3) When an approach has been loaded in

the navigation system, 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 not

already armed (some receivers arm automatically).
Without arming, the receiver will not change from
en route 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

Navigation Aids 1-1-21

Page 75 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   74 -- Page 75 -- 76