What happened
On 20 July 1999, a DC-8-62F, registration 9G-MKH, was undergoing cargo unloading and turnaround operations at Manston, Kent International Airport. During the process, an avionics engineer attempted to replace a GPS unit on the flight deck. Because the landing gear selector lever on this specific aircraft model obstructed the removal of the unit, the engineer moved the lever out of the DOWN position to provide clearance.
While the aircraft's hydraulic systems were unpressurised, a ground engineering supervisor requested to restore hydraulic power to facilitate maintenance on a wheel well component. Upon activating the auxiliary hydraulic pump, the nose landing gear retracted approximately 20 to 30 seconds later. The sudden collapse of the nose caused the aircraft to drop violently, resulting in one serious injury and four minor injuries among the ground staff and crew.
The investigation
The AAIB investigation focused on why the landing gear lever moved into a position that allowed retraction. Investigators found that the engineer had moved the lever to clear the GPS unit, potentially during a transient period where the weight-on-wheels system briefly entered 'air mode' due to shifts in the aircraft's center of gravity during cargo movement.
Testing revealed that once the lever was lifted past a certain point, it could unexpectedly creep or jump into a check detent position. If the lever reached this position, hydraulic fluid could be directed to the gear-up lines. The investigation also noted that the flight crew and supervisor were unaware that the landing gear lever had been disturbed, and the request to pressurise the hydraulics was not explicitly refused by the pilots.
Findings
- The nose landing gear retracted because the selector lever had been moved to a position that allowed hydraulic fluid to reach the retraction lines.
- A lack of coordination between the flight crew, the engineering supervisor, and the avionics engineer contributed to the incident.
- The avionics engineer performed an improvised procedure without a formal worksheet or supervision.
- The ground engineering supervisor and flight crew failed to verify the position of the landing gear controls before applying hydraulic power.