What happened
On January 23, 1999, an Air Liberté Fokker 100, registration F-GNLH, was operating a scheduled flight from London to Bordeaux. Upon landing on runway 23, the flight crew noticed the aircraft pulling to the left and experienced uncommanded braking on the left side during the rollout.
After exiting the runway, the aircraft came to a stop on taxiway Papa 3. The crew observed smoke emanating from the left main landing gear. Emergency services were deployed and quickly managed the situation. As a precaution, the 45 passengers and 5 crew members were evacuated through the front right door without incident.
The investigation
The investigation focused on the hydraulic connection coupling (self-connection) of the left main landing gear. This component consists of two quick-connect fittings that screw together. The investigation examined the maintenance history and the physical condition of the hardware.
Analysis of the maintenance recorder (QAR) confirmed that during the landing, the aircraft's longitudinal and lateral accelerations showed the aircraft was braking and veering to the left. Physical inspection of the coupling revealed significant wear on the spring ring and excessive wear on the braking notches. The upper collar of the ring was broken, and there were visible marks from the use of pliers, despite the component being designed for hand-tightening. Additionally, the check valve in the fitting showed signs of impact, likely from previous brake assembly/disassembly work. The investigation also noted that the safety wire was broken.
Findings
- The primary cause of the incident was a maintenance failure that led to the disconnection of the hydraulic connection coupling on the left main gear.
- The coupling could not be fully tightened because the worn spring ring created a hard point during assembly.
- The broken safety wire meant there was nothing to prevent the components from separating under pressure.
- Once the coupling partially separated, the internal check valves prevented hydraulic fluid from leaking, but effectively trapped the existing braking pressure. This caused the left brake to remain applied even as the pilot reduced braking pressure, leading to the asymmetric pull and the resulting heat and smoke.
- The component was in a condition that should have prompted replacement during the last brake assembly change on September 23, 1997.