Its Official Now , through 'AAIB SPECIAL Bulletin S1/2021' , United Kingdom's Air Accidents Invetigation Branch (AAIB) released the Circumstances and Cause of the Nose Landing Gear(NLG) Collapse of B787-8 (G-ZBJB) aircraft on 18 June 2021.
8 years old British Airways Boeing B787-8 (G-ZBJB) aircraft sustained a NLG (Nose Landing Gear) collapse while parked on a gate near 5C of London-Heathrow International Airport, UK while preparing for a flight to Frankfurt.
As the aircraft was preparing for the flight to Frankfurt, three ground engineers on the flight deck were engaged in maintenance activity to clear three status messages associated with an Acceptable Deferred Defect (ADD) for a NLG door-closed solenoid valve.
While carrying out the Dispatch Deviation Guide (DDG) procedure to clear maintenance messages relating to the existing ADD, the Nose Landing Gear (NLG) retracted due to a sequence of events.
In order to defer the three defects highlighted by the NLG status messages messages, the DDG for the aircraft required hydraulic pressure to be applied and the cockpit landing gear lever to be cycled from down to up then returned to down.
During the Landing Gear Selection lever recycling process, to prevent the landing gear from retracting, the maintenance procedure required pins to be inserted in the nose and main landing gear downlocks.
To comply the requirements, the Lead Engineer instructed the lead mechanic and another mechanic to install the landing gear locking pins on Both NLG and MLG Down Locks.
However, the NLG downlock pin was installed in the NLG downlock apex pin bore which was adjacent to the correct hole location to install the downlock pin. When the landing gear selector was cycled the NLG retracted.
This caused damage to the lower nose, NLG doors and engine cowlings. Door 2 left (Door 2L) struck the top of the mobile steps which resulted in the door separating from the fuselage and one person, operating the cargo loader positioned at the forward cargo hold, received minor injuries.
An Airworthiness Directive had already been issued, with a 36-month compliance from 16 January 2020, to install an insert over the apex pin bore to prevent incorrect installation of the downlock pin, but this had not yet been implemented on G-ZBJB.
In 2018, another Boeing 787 experienced a retraction of the NLG while the aircraft was on the ground which had been caused by the NLG downlock pin being accidentally installed in the apex pin inner bore, which is adjacent to the correct hole for the downlock pin in the NLG lock link assembly.
As a result of this event the aircraft manufacturer published Issue 01 of Service Bulletin (SB) B787-81205-SB320040-00 on 12 March 2019. The SB provides instructions to install an insert into the NLG lock link apex pin inner bore.
The insert prevents the NLG downlock pin from being inserted in the apex pin bore instead of the adjacent NLG downlock pin hole. Issue 02 of the SB was subsequently published on 23 October 2020.
Incorporation of SB B787-81205-SB320040-00 was subsequently mandated by FAA Airworthiness Directive (AD) 2019-23-07, published on 16 January 2020. The AD specified a compliance time of 36 months from the date of publication. This had not yet been implemented on G-ZBJB.
Source : AAIB SPECIAL Bulletin S1/2021.
