FAA issues emergency airworthiness directive after worries over inertial sensors
Boeing 777 operators have had to reinstall old software to stop the possible in-flight failure of Honeywell air data inertial reference units (ADIRUs) that rely on newer software.
An emergency airworthiness directive (AD) issued by the US Federal Aviation Administration says operational program software (OPS) versions approved since 1998 will accept data from failed sensors.
“OPS using data from faulted sensors, if not corrected, could result in anomalies of the fly-by-wire primary flight-control, autopilot, autothrottle, pilot display and auto-brake systems, which could result in high pilot workload, deviation from the intended flightpath, and possible loss of control of the aircraft,” says the FAA.
The emergency AD follows a Boeing service bulletin issued on 26 August, itself the result of an ongoing investigation into the 1 August failure of a Malaysia Airlines 777-200ER flight management system while climbing through 36,000ft (11,000m) soon after take-off from Perth airport in Australia.
“The flight crew disconnected the autopilot and stabilised the aircraft, during which time the aircraft climbed above 41,000ft, decelerated to a minimum speed of 158kt, and activated the stick shaker,” says the AD.
“A review of the flight data recorder shows there were abrupt and persistent errors in the outputs of the ADIRU. These errors were caused by the OPS using data from faulted sensors,” says the directive.
In April, the FAA issued an AD requiring 777 operators to upgrade to a later OPS version to prevent the display of erroneous heading information caused by a fault in the ADIRU software. The emergency AD requires operators to revert to the earlier software version. Honeywell is working on a fix.
DARREN SHANNON/WASHINGTON DC
Source: Flight International
