smartt1982
Topic Author
Posts: 226
Joined: Sat Nov 24, 2007 11:17 pm

AA191 And The V2 Increment

Tue Feb 26, 2013 12:45 pm

In the crash report of the AA191 it was mentioned that American Airlines amended their procedures for pilots to follow in the event of an engine failure on take off ie V2 + 10 if carrying excess speed above this. This was done to provide more of a margin above V2.
I know V2 is the minimum speed and does not give as good a climb profile as best abgle/rate but what is the reason for having this excess speed? Why 10 knots? On the Boeing 737 our FD will command a speed of V2 to V2+20.
Just wondering if anyone can point me to the specifics of +10 or 20 knots? Is it to prevent another AA191 crash as in the slats retract thereby increasing the stall speed for that wing, seems like a very specific fix for one sort of problem.
 
rcair1
Crew
Posts: 1144
Joined: Wed Oct 28, 2009 8:39 pm

RE: AA191 And The V2 Increment

Tue Feb 26, 2013 2:41 pm

If you read the NTSB report (http://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR79-17.pdf) you will see that the increase in speed is a result of the factors in this crash.

Specifically:
- When the left engine departed the aircraft - it damaged the leading edge slats on the left wing and the hydraulic lines controlling those slats.
- Because the DC 10 design did not include positive lock on the slats - when pressure was lost - the slats retracted increasing the stall speed of the left wing.
- Due to loss of the #1 Generator, the captian's stick shaker and, more importantly, the slat position compare warning was not effective. That system could have been restored, but there is no indication the crew attempted to do so - probably due to time available to them. The aircraft did not have a stick shaker on the right seat.
- The wings are not visible from the cockpit so the crew was unaware of the uncommanded slat retraction.
- The engine out procedure at the time included climbing at V2 accelerating to V2+6 after obstacle clearance.
- At V2 - the left wing stalled and the aircraft rolled. The crew had no indication of the impending or actual asymmetric stall.
- It was determined that if the crew had flown a faster profile - V2+10 - the a/c would have remained controllable.

Hence - the engine out climb profile was modified for higher speed.
Locking slat design was also mandated.
rcair1
 
Max Q
Posts: 5743
Joined: Wed May 09, 2001 12:40 pm

RE: AA191 And The V2 Increment

Tue Feb 26, 2013 5:35 pm

Quoting smartt1982 (Thread starter):


In the crash report of the AA191 it was mentioned that American Airlines amended their procedures for pilots to follow in the event of an engine failure on take off ie V2 + 10 if carrying excess speed above this. This was done to provide more of a margin above V2.
I know V2 is the minimum speed and does not give as good a climb profile as best abgle/rate but what is the reason for having this excess speed? Why 10 knots? On the Boeing 737 our FD will command a speed of V2 to V2+20.
Just wondering if anyone can point me to the specifics of +10 or 20 knots? Is it to prevent another AA191 crash as in the slats retract thereby increasing the stall speed for that wing, seems like a very specific fix for one sort of pro

Despite rcair's detailed and accurate reply Wadrs he didn't really answer your question.


On the older Aircraft with less performance than modern twins it was essential to fly V2 or + 10 to achieve the required climb gradient.


Modern twins have so much excess performance that, generally, if you 'hold what you've got' even if its 20 knot faster than V2 you will meet all performance requirements.
The best contribution to safety is a competent Pilot.
 
rcair1
Crew
Posts: 1144
Joined: Wed Oct 28, 2009 8:39 pm

RE: AA191 And The V2 Increment

Wed Feb 27, 2013 1:22 am

Quoting Max Q (Reply 2):
Despite rcair's detailed and accurate reply Wadrs he didn't really answer your question.

You're right! I missed the second half of the question entirely - thanks!
rcair1

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