Introduction
An incident involving an aircraft operating in Australia resulted in a flap disagreement warning and a subsequent return to Adelaide Airport. The event was investigated by the relevant aviation safety authority, which identified a bracket failure as the cause.
Incident Details
During climb, the left-hand outboard flap could not be fully retracted. This triggered a flap disagreement warning in the cockpit. The flight crew experienced no adverse control or handling issues and decided to return the aircraft to Adelaide Airport. The flaps were extended normally for landing without further problems.
Investigation Findings
Examination revealed that a pre-existing crack on a partially concealed bracket had propagated to the point where it failed in overstress during normal operation. The origin and age of the crack could not be determined, so it is not known whether there was an opportunity for it to have been detected during a base check conducted in 2014.
The exact mechanism by which the failed bracket prevented flap retraction was unclear, but it may have been caused by a bracket fragment physically obstructing the flap.
Risk Controls and Response
All risk controls during this incident worked well. The aircraft’s flap monitoring system identified the misalignment of the outboard flaps and prevented an asymmetry from occurring. The crew were adequately warned of the fault and advised air traffic control of the situation. They followed the quick reference handbook in an attempt to rectify the problem, but when the fault could not be cleared, they returned the aircraft to Adelaide Airport. A contingency plan was formulated in the event the flaps could not be extended, but ultimately it was not necessary.
Conclusion
The incident was attributed to a pre-existing crack in a bracket that failed under normal operating loads. No injuries or aircraft damage were reported.