“Inboard Flap Asymmetry B757 cannot recover?”, Boeing”we know but cannot happen because….features”. It happened.

Flap asymmetry:What happens if the Flaps don’t retract?

American Airlines got their first few Boeing 757 aircrafts in 1990’s. The check airmen got their toys, the flight simulator to play around with. During the play session on one of the full flight simulators, they discovered that when a failure of Inboard Flap Asymmetry was simulated by pushing a button on the instructor control panel, the resultant effect on the aerodynamics created an irrecoverable situation.

Boeing was queried immediately and they were very candidly told that what American Airlines was saying was absolutely true. What followed later was taken down with a pinch of salt.

Boeing said that the situation would never arise since there are …….. safety features which would prevent the situation from arising. American Airlines, decided to remove the exercise from the flight simulator training as a management decision.

Guess what?. It happened not once but twice on other air carriers. One in-flight and the other on ground. The presence of mind of the Captain saved the day. As soon as the asymmetry happened on selection of flap, and the crew concluding that the aircraft would was uncontrollable, the Captain retracted the flap and the flap retracted, thereby removing the asymmetry and restoring stability.

American Airlines introduced this as a procedure to overcome the problem. The residual risk was, what if the flap did not retract? In the later scenario, there is no way out.

Airworthiness directive (AD), applicable to certain Boeing Model 757 series airplanes, that currently requires repetitive inspections for excessive wear of the internal and external splines of the torque tube couplings of the trailing edge flaps, and replacement of the couplings, if necessary. 

American Airlines Video
https://mindfly.blog/2019/06/27/a-question-of-safety-or-ethicsboeing-737/
 

Author: Capt. Amit Singh

I think therefore I am https://www.linkedin.com/in/traintofly/ Airlines Operations and Safety balance expert. A former head of operations/training and safety of successful LCC's in India. An experienced member of the startup teams of these airlines has hands-on experience in establishing airlines systems and processes.

2 thoughts on ““Inboard Flap Asymmetry B757 cannot recover?”, Boeing”we know but cannot happen because….features”. It happened.

  1. Thanks for your writings….Finally deciphered how to comment on your blog. I have some queries. Since flaps have considerable surface area any asymmetric would have large effect on the lift. Unless the asymmetric is very small wherein asymmetric thrust and full aileron can hold off the bank, any significant asymmetry would render aircraft uncontrollable. There have been many cases of fuselage fire where the flaps got retracted asymmetrically and the aircraft rolled over into the ground. The manufacturer try to put in as many features to stop this type of anomaly (flap brakes ).

     

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