Recently, an operator reported that the wing flaps of a CRJ200 extended with no command while in cruise flight. The flight crew observed the EICAS flap indication showing an extension of the left flaps to 10 degrees, while experiencing a minor un-commanded roll to the right following autopilot disconnect.
During troubleshooting following the flight, the Flap Electronic Control Unit (FECU) and flap Power Drive Unit (PDU) were replaced. Prior to removal, the fault logs of the FECU were interrogated, and no faults were logged for the applicable flight leg. During a subsequent ferry flight, anomalous EICAS flap indications continued. Final resolution of the issue on the subject aircraft was achieved by replacement of the left Flap Position Transmitter Unit (FPTU).
The investigation of this event has determined that there was NOT an un-commanded flap deployment. What was perceived as a flap deployment was in fact due to an erroneous EICAS indication for the left flap (EICAS flap position indication is independent of the flap control system), coupled with the perception of a sympathetic physical response of the aircraft to the EICAS indication (it is possible for a small amount of roll mistrim to be present during autopilot operation, which can trigger minor rolling movements upon autopilot disengagement until the
aileron trim is adjusted).
While there have been several reported events similar to the one described above, uncommanded flap operation on the CRJ series fleet has never occurred. In all known reported events, the issue was resolved by rectification actions taken for the FPTUs, not for the flap control system.
Bombardier Aerospace will release a Service Letter in the near future to discuss technical details of the issue and to recommend appropriate actions when abnormal EICAS indications for flap position occur.
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