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23rd May 2011, 20:10
Turbine D

Join Date: Dec 2010
Location: Middle America
Age: 81
Posts: 1,163
Time To Impact

On the other AF 447 thread in R&N, there is an interesting Post # 377 by MFgeo. In this post there is a link to an author (Matthew Squair) where he has calculated the time to impact using information provided by the BEA in their Interim Report #1. With additional information provided by the BEA in Interim Report #2 he revised his figures accordingly.

Based on a terminal airspeed derived from the cabin pressure advisory message, the time to impact (tti) can be calculated as being 57 seconds after the cabin vertical speed advisory was generated (2:14:21).
This would result in a time of impact (toi) of 2:15:23.
But, these tti and toi are based upon the assumption of an average terminal vertical velocity in the last 57 seconds of flight that is the same as the average calculated for the preceding flight phase.
As a still flying aircraft would have transmitted the class 2 ADR 2 fault message before impact these two times can be used to revise the time to impact (tti) and correct the terminal velocity (vterm).
He previously calculated the altitude at which the safety valve opened (6,898.5 ft) and he believed that the valve opened at 2:14:26, 5 seconds before the advisory would have triggered and he calculated the terminal velocity associated with both ends of the transmission window as follows.
In the case of (time to impact) timp = 2:15:00:
tti (2:15:00) = 2:14:26 – 2:15:00 = 0:00:34 seconds.
Giving an average terminal velocity of:
vterm (2:15:00) = 6,898.5 ft / 34 sec = 12,173.9 ft / min.
In the case of timp = 2:15:14:
tti (2:15:14) = 2:14:26 – 2:15:14 = 0:00:48 seconds.
Giving an average terminal velocity of:
vterm (2:15:00) = 6,898.5 ft / 48 sec = 8,623.1 ft / min.
The corrected results. Given the transmission window for the ADR 2 fault message the average terminal velocity of AF 447 is in the range 8,623.1 to 12,173.9 ft / min.
His Conclusions. The increase in average vertical velocity from 6,718 ft/min to at a minimum 8,623.1 f/min indicates a sustained vertical acceleration of the aircraft.
This terminal vertical acceleration and high terminal vertical speed when combined with the positive attitude and low bank of the aircraft is strongly indicative of the aircraft having departed into a deep stall and possibly a subsequent flat spin.

If his theory is correct, it might explain the relative closeness of the found debris to the LNP.

Last edited by Jetdriver; 23rd May 2011 at 21:20.