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Old 13th Apr 2010, 18:11
  #511 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 72
Posts: 2,408
alph2z;

The only animations which are of any use at all are those which are data-driven from the DFDR and, where it may survive, the QAR.

Anything else is from someone who has some skill with Google Earth or the many animation programs out there, and some imagination. As such, with these animations there is absolutely no basis in reality or fact so they should be completely ignored. Those doing such work, including any media, do not have access to DFDR information.

What is reliably known now is that the tree-breakage and wreckage pattern means the aircraft was low on the approach and in a low rate-of-descent regime rather than in a high rate-of-descent loss-of-control situation. This speaks to approach issues rather than operational/aircraft issues but why they were low cannot be established from what we know thus far.

That is why it would be helpful to know what approach was in use and what charts were being used by the flight crew and what those charts indicated.

Has it been firmly established that they were doing an NDB approach?

For others pondering the meaning of such approaches, an NDB approach is essentially a cloud-breaking procedure with questionable accuracy.

To add a bit of precision to the approach, a time (in minutes/seconds) to the runway threshold or, (better), the MDA, (minimum descent altitude) from the FAF (final approach fix) using a ground-speed chart and altitude to lose are provided on the chart along with a rate-of-descent.

This is intended to provide a uniform rate of descent towards the MDA, ideally reaching the MDA at or slightly before the time is up rather than what is called the "dive-and-drive" descent where high rates of descent obtain followed by a level-off for level-flight low to the ground and perhaps some distance away from the runway.

The timed approach with published rate of descent is so that the crew know when they should descend no further until they establish firm visual contact with the runway.

However, the temptation to scud-run (as the previous poster accurately states) once one sees a bit of the ground, can be very high. The result is a very high risk approach in poor visibility.

But because of accuracy issues (left or right of course) and the complete absence of vertical guidance and the illusions which may be caused by variations in terrain, (such as here), the civilian regulatory limitations on forward visibility are high on such approaches. If I recall from earlier posts, the visibility was around 400m, or very near/at CATII limits precluding any kind of non-precision approach.

PJ2

Last edited by PJ2; 13th Apr 2010 at 18:35.
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