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aircraft must begin descent to execute a safe landing.
It is developed based on terrain, obstructions,
NAVAID location and possibly air traffic considerations.
Because the MAP may be located anywhere
from well prior to the runway threshold to past the
opposite end of the runway, the descent from the
Minimum Descent Altitude (MDA) to the runway
threshold cannot be determined based on the MAP
location. Descent from MDA at the MAP when the
MAP is located close to the threshold would require
an excessively steep descent gradient to land in the
normal touchdown zone. Any turn from the final
approach course to the runway heading may also be
a factor in when to begin the descent.
12.10.1 Pilots are cautioned that descent to a
straight−in landing from the MDA at the MAP may
be inadvisable or impossible, on a nonprecision
approach, even if current weather conditions meet the
published ceiling and visibility. Aircraft speed, height
above the runway, descent rate, amount of turn and
runway length are some of the factors which must be
considered by the pilot to determine if a landing can
be accomplished.
12.10.2 Visual descent points (VDPs) provide pilots
with a reference for the optimal location to begin
descent from the MDA, based on the designed
vertical descent angle (VDA) for the approach
procedure, assuming required visual references are
available. Approaches without VDPs have not been
assessed for terrain clearance below the MDA, and
may not provide a clear vertical path to the runway at
the normally expected descent angle. Therefore,
pilots must be especially vigilant when descending
below the MDA at locations without VDPs. This does
not necessarily prevent flying the normal angle; it
only means that obstacle clearance in the visual
segment could be less and greater care should be
exercised in looking for obstacles in the visual
segment. Use of visual glide slope indicator (VGSI)
systems can aid the pilot in determining if the aircraft
is in a position to make the descent from the MDA.
However, when the visibility is close to minimums,
the VGSI may not be visible at the start descent point
for a “normal” glidepath, due to its location down the
runway.
12.10.3 Accordingly, pilots are advised to carefully
review approach procedures, prior to initiating the
approach, to identify the optimum position(s), and
any unacceptable positions, from which a descent to
landing can be initiated (in accordance with 14 CFR
Section 91.175(c)).
12.11 Area Navigation (RNAV) Instrument
Approach Charts. Reliance on RNAV systems for
instrument operations is becoming more
commonplace as new systems such as GPS and
augmented GPS such as the Wide Area
Augmentation System (WAAS) are developed and
deployed. In order to support full integration of
RNAV procedures into the National Airspace System
(NAS), the FAA developed a new charting format for
IAPs (See FIG ENR 1.5−20). This format avoids
unnecessary duplication and proliferation of
instrument approach charts. The original stand alone
GPS charts, titled simply “GPS,” are being converted
to the newer format as the procedures are revised.
One reason for the revision could be the addition of
WAAS based minima to the approach chart. The
reformatted approach chart is titled “RNAV (GPS)
RWY XX.” Up to four lines of minima are included
on these charts. GLS (Global Navigation Satellite
System [GNSS] Landing System) was a placeholder
for future WAAS and LAAS minima, and the minima
was always listed as N/A. The GLS minima line has
now been replaced by the WAAS LPV (Localizer
Performance with Vertical Guidance) minima on
most RNAV (GPS) charts. LNAV/VNAV (lateral
navigation/vertical navigation) was added to support
both WAAS electronic vertical guidance and
Barometric VNAV. LPV and LNAV/VNAV are both
3114 J FUELBY 08
ENR 1.5−36 AIP
15 MAR 07 United States of America
Nineteenth Edition Federal Aviation Administration
APV procedures as described in paragraph 12.1.7.
The original GPS minima, titled “S−XX,” for straight
in runway XX, is retitled LNAV (lateral navigation).
Circling minima may also be published. A new type
of nonprecision WAAS minima will also be
published on this chart and titled LP (localizer
performance). LP will be published in locations
where vertically guided minima cannot be provided
due to terrain and obstacles and therefore, no LPV or
LNAV/VNAV minima will be published. Current
plans call for LAAS based procedures to be published
　
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