What happened
On 4 December 1999, a Boeing 757-28A, registration G-FCLI, departed Manchester Airport for a scheduled flight to Las Palmas. Shortly after takeoff, during the retraction of the landing gear, the flight crew observed two caution messages on the Engine Indication and Crew Alerting System (EICAS) indicating a 'Gear Disagree' and 'Gear Doors' status. This was accompanied by an unusual noise from the ambient airflow.
Following established procedures, the crew maintained a speed below 270 kt. After consulting with engineering and operations, the crew attempted to recycle the landing gear while climbing through FL9/900. The recycling attempt failed to resolve the indications. Due to the speed limitations imposed by the gear configuration, the commander diverted the flight to London Gatwick Airport. The aircraft performed an overweight landing at Gatwick, which was approximately 4 tonnes above the maximum allowable landing weight, though the landing itself was uneventful and no injuries were reported among the 230 passengers or 9 crew members.
The investigation
Upon inspection at Gatwick, investigators found damage to the composite panels of the starboard main landing gear bay. The starboard landing gear truck was found to be fully retracted into the main leg, with the telescoped portion of the inner cylinder invisible. Attempts to extend the gear using hydraulic pressure were unsuccessful.
Subsequent borescope examination of the removed leg revealed significant deformation and major cracking near the upper end of the inner cylinder. The damage was characterized as compressive crippling. Metallurgical analysis of the fracture faces showed no pre-existing defects. Furthermore, evidence was found that the area surrounding the metering pin had made forceful contact with the orifice plate.
During the investigation, a second, unrelated aircraft of the same type was identified with a nearly identical failure. In that instance, the aircraft had experienced a slight nosewheel bounce during taxiing and subsequent gear retraction issues. The investigation also considered the possibility of 'dieseling'—rapid combustion of hydraulic fluid vapor—but found no evidence that the leg had been incorrectly charged with compressed air.
Findings
- The primary cause of the failure was the internal structural collapse of the inner cylinder due to compressive crippling.
- This deformation occurred when the metering pin surround struck the orifice plate travel stop.
- It is probable that the leg reached full compression due to an insufficient amount of hydraulic fluid, which would have left the fluid level below the orifice plate during the compression stroke, thereby removing the necessary damping function during firmer landings.