The Italian Air Safety Board, ANSV, issued an urgent safety recommendation to the U.S. Federal Aviation Administration (FAA) and European Aviation Safety Agency (EASA).
On June 13, 2009 a Boeing 737-700 airplane suffered an engine flameout while crossing 2500 feet on approach to Firenze (Florence) Airport, Italy. The engine was restarted in-flight and the airplane landed safely. The root of the problem was identified in the bleed air check valve stuck in the open position. The valve is designed to prevent reverse flow from 9th stage into the 5th stage of the High Pressure Compressor.
The investigators leared that in just over a year, the 737 NG fleet has experienced five engine shutdowns that were all caused by the 5th stage bleed air check valve stuck in the open or partially open position.
The ANSV classified this as a serious incident and issued an urgent safety recommendation on October 1, 2009.
ANSV based on previous considerations, recommends Federal Aviation Administration (FAA) and European Aviation Safety Agency:
– to consider requesting Boeing to build-up a pro-active procedure allowing flight crews to identify and manage the event of CFM56-7B22 engines 5th stage bleed air check valve stuck in the open position (ANSV-6/625-09/1/I/09);
– to verify the on-going manufacturer investigation process on the involved P/N, in order to determine if the failure is associated with the design of the part or with a production deviation occurrence which affects a limited number of Serial numbers.
Furthermore to ensure that the affected parts are replaced either if they are identified to belong to a specific batch or if is a fleet wide problem (ANSV-71625-0912/1/09). (ANSV)