Aeronautical Information Manual (AIM), page 358

Index   357 -- Page 358 -- 359


3. ILS or RNAV (GPS) charts.

(a) Some RNAV (GPS) charts will also con-

tain an ILS line of minima to make use of the ILS

precision final in conjunction with the RNAV GPS

capabilities for the portions of the procedure prior to

the final approach segment and for the missed ap-

proach. Obstacle clearance for the portions of the

procedure other than the final approach segment is

still based on GPS criteria.

Some GPS receiver installations inhibit GPS navigation
whenever ANY ILS frequency is tuned. Pilots flying
aircraft with receivers installed in this manner must wait
until they are on the intermediate segment of the procedure
prior to the PFAF (PFAF is the active waypoint) to tune the
ILS frequency and must tune the ILS back to a VOR fre-
quency in order to fly the GPS based missed approach.

(b) Charting. There are charting differences

between ILS, RNAV (GPS), and GLS approaches.

(1) The LAAS procedure is titled "GLS
RWY XX" on the approach chart.

(2) The VDB provides information to the

airborne receiver where the guidance is synthesized.

(3) The LAAS procedure is identified by a
four alpha-numeric character field referred to as the
RPI or approach ID and is similar to the IDENT fea-
ture of the ILS.

(4) The RPI is charted.

(5) Most RNAV(GPS) approach charts

have had the GLS (NA) minima line replaced by an

LPV line of minima.

(6) Since the concepts for LAAS and

WAAS procedure publication have evolved, GLS

will now be used only for LAAS minima, which will

be on a separate approach chart.

4. Required Navigation Performance (RNP).

(a) Pilots are advised to refer to the


(Section A) of the U.S. Government Terminal

Procedures books for aircraft approach eligibility
requirements by specific RNP level requirements.

(b) Some aircraft have RNP approval in their
AFM without a GPS sensor. The lowest level of
sensors that the FAA will support for RNP service is
DME/DME. However, necessary DME signal may
not be available at the airport of intended operations.

For those locations having an RNAV chart published
with LNAV/VNAV minimums, a procedure note may

be provided such as "DME/DME RNP-0.3 NA."

This means that RNP aircraft dependent on

DME/DME to achieve RNP-0.3 are not authorized to

conduct this approach. Where DME facility

availability is a factor, the note may read "DME/DME

RNP-0.3 Authorized; ABC and XYZ Required."

This means that ABC and XYZ facilities have been

determined by flight inspection to be required in the
navigation solution to assure RNP-0.3. VOR/DME
updating must not be used for approach procedures.

5. Chart Terminology.

(a) Decision Altitude (DA) replaces the
familiar term Decision Height (DH). DA conforms to
the international convention where altitudes relate to
MSL and heights relate to AGL. DA will eventually

be published for other types of instrument approach

procedures with vertical guidance, as well. DA
indicates to the pilot that the published descent profile
is flown to the DA (MSL), where a missed approach
will be initiated if visual references for landing are not

established. Obstacle clearance is provided to allow

a momentary descent below DA while transitioning
from the final approach to the missed approach. The
aircraft is expected to follow the missed instructions
while continuing along the published final approach
course to at least the published runway threshold
waypoint or MAP (if not at the threshold) before

executing any turns.

(b) Minimum Descent Altitude (MDA) has

been in use for many years, and will continue to be

used for the LNAV only and circling procedures.

(c) Threshold Crossing Height (TCH) has

been traditionally used in "precision" approaches as

the height of the glide slope above threshold. With

publication of LNAV/VNAV minimums and RNAV
descent angles, including graphically depicted
descent profiles, TCH also applies to the height of the

"descent angle," or glidepath, at the threshold. Unless

otherwise required for larger type aircraft which may

be using the IAP, the typical TCH is 30 to 50 feet.

6. The MINIMA FORMAT will also change

(a) Each line of minima on the RNAV IAP is
titled to reflect the level of service available; e.g.,
CIRCLING minima will also be provided.

5-4-22 Arrival Procedures

Page 358 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   357 -- Page 358 -- 359