What happened
During the sequence of events involving landing and taxiing, a mechanical failure occurred within the aircraft's landing gear assembly. Specifically, the wheel hub on the left main gear experienced a sudden fatigue fracture. This structural failure was not random; forensic examination revealed that the cracks initiating the fracture originated from the grease dam groove within the hub itself.
As the hub fractured, it caused significant collateral damage to other brake components in the vicinity. The destruction of these parts compromised the integrity of the hydraulic system, allowing hydraulic fluid to escape and leak onto a nearby brake pad. Because the brake pad was hot at the time, the leaked fluid ignited immediately, creating a fire hazard.
The investigation
The investigation focused on the root cause of the landing gear failure. Analysis confirmed that the primary point of failure was the fatigue fracture of the left main gear wheel hub. Investigators traced the origin of the cracks back to the grease dam groove, identifying this as the initiation site for the structural failure.
Findings
The sequence of events was driven by mechanical wear and material fatigue. The fatigue fracture of the wheel hub was the initiating event. This fracture damaged brake components, leading to a hydraulic leak. The presence of hot brake pads provided the ignition source for the leaked hydraulic fluid. The combination of structural failure in the gear hub and subsequent thermal ignition highlights the critical nature of maintenance intervals for landing gear components.
Safety message
Regular inspection of landing gear wheel hubs, particularly around grease dam grooves, is essential to detect early signs of fatigue cracking before catastrophic failure occurs.