Aeronautical Information Manual (AIM), page 354

Index   353 -- Page 354 -- 355


considered for obstacle clearance and may be lower
than the LNAV/VNAV DA, but never lower than the
straight in LNAV MDA. This may occur when
different controlling obstacles are used or when other
controlling factors force the LNAV MDA to be higher
than 250 feet above the LNAV OCS. In FIG 5-4-11,
the required obstacle clearance for both the LNAV
and Circle resulted in the same MDA, but lower than
the LNAV/VNAV DA. FIG 5-4-12 provides an
illustration of this type of situation.
3. Vertical guidance (LNAV/VNAV). A line is
drawn horizontal at obstacle height until reaching the
obstacle clearance surface (OCS). At the OCS, a
vertical line is drawn until reaching the glide path.
This is the DA for the approach. This method places
the offending obstacle in front of the LNAV/VNAV
DA so it can be seen and avoided. In some situations,
this may result in the LNAV/VNAV DA being higher

than the LNAV and/or Circling MDA.

h. The Visual Descent Point (VDP), identified by
the symbol (V), is a defined point on the final
approach course of a nonprecision straight-in
approach procedure from which a stabilized visual
descent from the MDA to the runway touchdown

point may be commenced. The pilot should not

descend below the MDA prior to reaching the VDP.

The VDP will be identified by DME or RNAV

along-track distance to the MAP. The VDP distance

is based on the lowest MDA published on the IAP and

harmonized with the angle of the visual glide slope
indicator (VGSI) (if installed) or the procedure VDA
(if no VGSI is installed). A VDP may not be
published under certain circumstances which may
result in a destabilized descent between the MDA and
the runway touchdown point. Such circumstances
include an obstacle penetrating the visual surface
between the MDA and runway threshold, lack of
distance measuring capability, or the procedure
design prevents a VDP to be identified.

1. VGSI systems may be used as a visual aid to
the pilot to determine if the aircraft is in a position
make a stabilized descent from the MDA. When the
visibility is close to minimums, the VGSI may not be
visible at the VDP due to its location beyond the
2. Pilots not equipped to receive the VDP should
fly the approach procedure as though no VDP had
been provided.

3. On a straight-in nonprecision IAP, descent
below the MDA between the VDP and the MAP may
be inadvisable or impossible. 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 safe descent
and landing can be accomplished.
i. A visual segment obstruction evaluation is ac-
complished during procedure design on all IAPs.
Obstacles (both lighted and unlighted) are allowed to
penetrate the visual segment obstacle identification
surfaces. Identified obstacle penetrations may cause
restrictions to instrument approach operations which
may include an increased approach visibility require-
ment, not publishing a VDP, and/or prohibiting night
instrument operations to the runway. There is no im-
plicit obstacle protection from the MDA/DA to the
touchdown point. Accordingly, it is the responsibility
of the pilot to visually acquire and avoid obstacles be-

low the MDA/DA during transition to landing.
1. Unlighted obstacle penetrations may result in
prohibiting night instrument operations to the
runway. A chart note will be published in the pilot
briefing strip "Procedure NA at Night."

2. Use of a VGSI may be approved in lieu of

obstruction lighting to restore night instrument

operations to the runway. A chart note will be

published in the pilot briefing strip " Straight-in Rwy

XX at Night, operational VGSI required, remain on

or above VGSI glidepath until threshold."

j. The highest obstacle (man-made, terrain, or ve-
getation) will be charted on the planview of an IAP.
Other obstacles may be charted in either the planview
or the airport sketch based on distance from the run-
way and available chart space. The elevation of the
charted obstacle will be shown to the nearest foot
above mean sea level. Obstacles without a verified
accuracy are indicated by a ± symbol following the
elevation value.
k. Vertical Descent Angle (VDA). FAA policy is
to publish VDAs on all nonprecision approaches ex-
to cept those published in conjunction with vertically
guided minimums or no-FAF procedures without
step-down fixes. A VDA does not guarantee obstacle
protection below the MDA in the visual segment. The
presence of a VDA does not change any nonprecision
approach requirements.
1. Obstacles may penetrate the visual segment
of an IAP that has a published VDA. When the VDA

5-4-18 Arrival Procedures

Page 354 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   353 -- Page 354 -- 355