What happened
On 16 August 2015, a British Aerospace 1s6-200, registration D-AMGL, arrived at London City Airport on a scheduled passenger service from Frankfurt. The flight, carrying 77 passengers and 4 crew members, proceeded with a normal approach and landing. The commander noted a touchdown that was strongly positive with a slight bounce, a detail corroborated by airport CCTV.
Following the landing, the aircraft taxied to its parking stand without any reported warnings or cockpit indications of a malfunction. However, once parked, ground personnel alerted the crew to fluid leaking from the right main landing gear. The crew observed that the aircraft was beginning to tilt slightly to one side. Upon inspection, the commander identified an oil leak and a puncture in the right main gear door.
The investigation
The AAIB investigation focused on the source of the fluid loss and the physical damage to the landing gear. Inspections revealed that the head of a bolt on the shock-absorber was missing, and oil was visibly bubbling from the site of the failure. The investigation also examined the landing gear door, finding a hole consistent with the missing bolt head being forced against the door structure during gear retraction.
Technical analysis of the shock-absorber was conducted by the manufacturer. Metallurgical examination of the fractured bolt revealed multiple fatigue cracks at the interface between the bolt and the outer cylinder. Furthermore, the investigation reviewed maintenance records and the aircraft's Flight Data Recorder (FDR) to determine the operational history of the component.
Findings
- The primary cause of the incident was the fracture of a shock-absorber bolt due to fatigue.
- The bolt had exceeded its established 18,100 landing fatigue-life limit, having completed at least 21,000 landings.
- There was evidence suggesting the remaining attachment bolts may have been over-torqued during previous maintenance, which could have contributed to the failure.
- At the time of the occurrence, the operator was not monitoring the specific landing life of these bolts, as records were not inherited from the previous owner.
- The design of the shock-absorber ensures that a loss of oil of this magnitude does not significantly degrade aircraft performance.
Safety action
Following the investigation, the operator implemented a new system to specifically record and monitor the number of landings for the bolts on the shock-absorbers to ensure they are replaced before reaching their fatigue life limit.