Gattaca
17th Apr 2007, 21:50
Jeppessen Charts don't show this point.
How does one calculate this for a Jet say A320?
How come Turbo Props use this point more commonly than Jets?
Capt Claret
17th Apr 2007, 23:05
Not heard the term used, what does it mean?
Below is what is in my company's ops specs. With CANPA now in full swing, consideration of VDPs has become nearly obsolete. They are an important part of the equation for non-CANPA approaches, and when published are included in the brief.
Visual Descent Point (VDP)
The VDP is the point at which a three degree glide slope from the threshold
intersects the Minimum Descent Altitude (MDA).
Published VDP
Some non-precision approach charts depict a VDP, usually identified as a DME
fix. The VDP is identified in the profile view of an approach chart by the symbol “V”
and is intended to provide additional vertical guidance. It is a defined point on the
final approach course of a non-precision straight-in approach procedure from
which a normal descent from the MDA to the runway touchdown zone may
commence, provided that the necessary visual reference has been established.
If the pilot has acquired the necessary visual reference prior to reaching the VDP,
he should realize that he has not yet reached the point to begin a normal descent.
Conversely, if the pilot has not acquired the necessary visual reference at the
VDP, he should anticipate that a missed approach is likely.
While maintaining MDA, the pilot may not descend below MDA prior to reaching
the published VDP, even if he acquires the necessary visual reference.
NOTE: There is one rare exception to this rule. FAR 121.651 states that the pilot
may leave MDA prior to reaching the published VDP if he has acquired the
necessary visual reference and a descent to the runway cannot be made using
normal procedures or rates of descent if descent is delayed until reaching the
published VDP
Also, from the FAA's IPH:
http://www.faa.gov/library/manuals/aviation/instrument_procedures_handbook/media/CH-05.pdf
For short runways, arriving at the MDA at the MAP
when the MAP is located at the threshold may require a
missed approach for some airplanes. For nonprecision
approaches a descent rate should be used that will
ensure that the airplane reaches the MDA at a distance
from the threshold that will allow landing in the touchdown
zone. On many IAPs this distance will be annotated
by a VDP. To determine the required rate of
descent, subtract the TDZE from the FAF altitude and
divide this by the time inbound. For example if the
FAF altitude is 2,000 feet MSL, the TDZE is 400 feet
MSL and the time inbound is two minutes, an 800
FPM rate of descent should be used.
To verify the airplane is on an approximate 3° glidepath,
use a calculation of “300-foot-to 1 NM.” The
glidepath height above TDZE is calculated by multiplying
the NM distance from the threshold by 300.
For example, at 10 NM the aircraft should be 3,000
feet above the TDZE, at 5 NM 1,500 feet, at 2 NM
600 feet, at 1.5 NM 450 feet, etc., until a safe landing
can be made. In the above example the aircraft should
arrive at the MDA (800 feet MSL) approximately 1.3
NM from the threshold and in a position to land in the
touchdown zone.