What happened
On 18 June 2021, a Boeing 787-8, registration G-ZBJB, was undergoing maintenance at London Heathrow Airport in preparation for a cargo flight to Frankfurt. Ground engineers were working to clear maintenance messages related to a defect in a nose landing gear (NLG) door-closed solenoid valve. To clear these messages, a procedure required the application of hydraulic power and the cycling of the landing gear lever in the cockpit.
To ensure safety during this process, the procedure required landing gear locking pins to be inserted into the nose and main landing gear downlocks to prevent accidental retraction. While the engineers were performing the task, the nose landing gear unexpectedly retracted. This caused the aircraft nose to strike the ground, impacting a ground power unit cable arm. The movement also caused the aircraft to sink, leading the left passenger cabin door to strike mobile steps, which resulted in the door separating from the fuselage.
During the incident, one person operating a cargo loader and the co-pilot sustained minor injuries. The aircraft sustained damage to the lower forward fuselage, the engine cowlings, and the NLG doors.
The investigation
The AAIB investigation established that the nose landing gear retracted because the NLG downlock pin had been incorrectly installed. Instead of being placed in the correct downlock pin hole, the pin was inserted into the adjacent apex pin bore. This error meant the gear was not actually secured against retraction.
Investigators found that a previous similar event in 201 and a subsequent Airworthiness Directive (AD) had been issued to prevent this specific error. The directive required the installation of an insert over the apex pin bore to make incorrect installation impossible. However, this modification had not yet been implemented on G-ZBJB.
Findings
- The nose landing gear retracted because the NLG downlock pin was installed in the incorrect location (the apex pin bore).
- An existing Airworthiness Directive intended to prevent this error via a hardware insert had not yet been completed on the aircraft.
- The ground engineers had followed the procedure for cycling the gear lever but the physical safeguard (the pin) was not functional due to its misplacement.