Boeing 737 operators were expected to have completed checks at the end of last week on almost 50 Next Generation aircraft believed to be fitted with potentially defective flight control modules (FCM). The emergency airworthiness directive (AD) was issued by the US Federal Aviation Administration on 13 September after the agency received reports of several FCM failures. The Smiths Aerospace-supplied FCM controls the flow of hydraulic fluid to the aileron, elevator and rudder power control units (PCU) on the 737-600, -700, -800 and -900 models, and is available for retrofit on older 737s. Failed FCM compensators have caused a build-up of hydraulic pressure within the PCUs, resulting in sluggish control responses, says the FAA. "Failure of one FCM could result in reduced controllability. Failure of both FCMs could result in loss of control of the aircraft," it adds.

Source: Flight International