Known Maintenance Risk Led To 787 Gear Collapse, UK’s AAIB Finds

787 gear collapse
Credit: AAIB

A British Airways 787-8’s inadvertent nose-gear retraction at a London Heathrow gate last month was caused by an incorrectly placed pin during routine maintenance—a design-related risk that regulators flagged in an airworthiness directive that had not been implemented on the aircraft, an interim report by the U.K.’s Air Accidents Investigation Branch (AAIB) found. 

The aircraft, G-ZBJB, was being loaded for an all-cargo flight to Frankfurt June 18 when the incident took place. While being loaded, a team of three technicians were clearing fault messages linked to a nose landing gear (NLG) solenoid valve. Issue was deferrable, so no immediate maintenance was necessary. But clearing the messages required applying hydraulic pressure and commanding the landing gear to raise and lower, according to the aircraft’s dispatch deviation guide (DDG). 

The process requires installing downlock pins in each gear bogie to prevent the landing gear from moving. On the nose gear, however, one technician inadvertently put the pin in an adjacent gap, or apex pin bore. While all three technicians took steps to confirm the pins were installed, they failed to realize the NLG was adjacent to its required position. 

When the landing gear level was selected to “UP,” the 787’s nose lowered to the ground. One member of the ground-loading team was “slightly injured,” the AAIB said. The aircraft’s NLG doors, lower fuselage, and engine cowlings were damaged.

A similar issue several years ago prompted Boeing to recommend all 787 operators install an insert in the pin bore and lock it with a cotter pin to prevent mechanics from misplacing the downlock pin. The FAA and EASA mandated Boeing’s instructions in January 2020, giving operators 36 months to do the work. G-ZBJB had not undergone the modification. 

Some operators recognized the risk before Boeing’s bulletin and took matters into their own hands. United Airlines filled its 787s’ pin bores with sealant, it told the FAA in comments during the rulemaking. The agency said the move, while effective, ran the risk of the sealant deteriorating, and said United should follow the directive.  

British Airways did not ignore the issue. It issued a “technical news leaflet” to its engineers in April 2020 highlighting the risk and correct installation of the downlock pin. It re-issued the same bulletin in December 2020. Following the incident, it decided to expedite compliance with the pin bore installation directive. 

“The investigation continues and will consider the safety procedures associated with landing gear maintenance, and the factors which may have contributed to the NLG downlock pin being incorrectly installed in the apex pin inner bore,” the AAIB wrote. 

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.