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NTSB recommends ATR-42 stick pusher AOA changes
29 June 2012

The ATR-42 as it came to rest near the runway at Lubbock, TX

The U.S. National Transportation Safety Board issued four additional safety recommendations in the wake of a non-fatal ATR-42 accident at Lubbock Airport, TX in 2009. The NTSB recommends to revise the stick pusher’s activation angle of attack (AOA) on ATR 42-series airplanes.

On January 27, 2009, an ATR 42-320 operating as Empire Airlines flight 8284, was on an instrument approach when it crashed short of the runway at Lubbock-Preston Smith International Airport, Texas. The captain sustained serious injuries, and the first officer sustained minor injuries. The airplane was substantially damaged.

The NTSB determined that the probable cause of  this accident was the flight crew’s failure to monitor and maintain a minimum safe airspeed while executing an instrument approach in icing conditions, which resulted in an aerodynamic
stall at low altitude.

A further review by the NTSB showed that current guidance emphasizes reducing the AOA as the primary means to stall prevention, and the stick pusher is intended to aid the pilot in that action. However, the NTSB is  concerned that, for in-service stick pusher-equipped transport-category airplanes, if the activation angle of the stick pusher is not reduced in icing conditions, its benefit in reducing the airplane’s AOA prior to stall and during recovery efforts is lost. The NTSB concludes that a lower stick pusher activation AOA would enhance safety in icing conditions and provide stall protection
before an uncommanded roll develops during stall.

Therefore, the NTSB recommends the FAA to:

  1. Require that Avions de Transport Régional (ATR) 42-series airplanes operating in the United States incorporate a revised stick pusher activation angle of attack (AOA), such that the stick pusher activates before the stall AOA in the presence of airframe ice accretions.
  2. Evaluate all  U.S.-certificated  transport-category airplanes  equipped with stick pushers  to ensure that the stick pusher  activates at an angle of attack that will provide adequate  stall  protection in the presence of  airframe  ice accretions.

And the NTSB recommends EASA to:

  1. Require  Avions de Transport Régional (ATR) to revise the stick pusher’s activation  angle of attack (AOA)  on ATR 42-series airplanes  to ensure that the stick pusher activates  before the stall AOA in the presence of airframe ice accretions.
  2. Evaluate all  European Aviation Safety Agency-certificated  transport-category airplanes equipped with stick pushers to ensure that the stick pusher activates at an  angle of  attack that will  provide adequate stall  protection in the presence of airframe ice accretions.

 

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