What happened
During the climb phase of flight, the aircraft experienced a flap disagreement warning. The failure was triggered when a bracket supporting the left-hand outboard flap shroud fractured, which prevented the flap from retracting fully. While the exact mechanism of the obstruction was not confirmed, it is believed that a fragment from the failed bracket may have physically blocked the flap's movement.
Despite the mechanical issue, the flight crew did not encounter any difficulties with aircraft control or handling. The crew followed established procedures, including consulting the quick reference handbook, in an attempt to resolve the fault. After being unable to clear the warning, the crew notified Air Traffic Control and elected to return the aircraft to Adelaide Airport. The flaps functioned normally during the landing phase without further complications.
The investigation
The investigation focused on the structural integrity of the flap shroud support. It was determined that a pre-existing crack on a partially concealed bracket had propagated until the component failed due to overstress during normal operations. Investigators were unable to establish the exact origin or age of the crack, leaving it uncertain whether the defect could have been identified during a base maintenance check performed in 2014.
Findings
- A pre-existing crack in a bracket led to a structural failure due to overstress.
- The failure of the bracket prevented the left-hand outboard flap from retracting fully.
- The aircraft's flap monitoring system successfully identified the misalignment, preventing a flap asymmetry.
- All established risk controls and crew responses were effective, including the formulation of a contingency plan for flap extension failure.