Dreamliner Pre-flight Maintenance
On Wednesday, the 16th of June, British Airways flight 881 from Moscow arrived at Heathrow airport. The aircraft was registration G-ZBJB, a Boeing 787-8 which had been converted from a passenger aircraft to cargo transport. This was one of four Dreamliner aircraft that British Airways began operating in 2013.
The next scheduled flight for the Dreamliner was on Friday the 18th, a cargo flight from London to Frankfurt. The flight crew arrived at the airport at 6:20 and went straight to the aircraft.
There, they found three ground engineers in the cockpit doing pre-flight maintenance. The aircraft had thrown up three status messages related to an Acceptable Deferred Defect, a door-closed solenoid valve related to the nose landing gear.
The engineers told the flight crew that they needed about forty minutes to finish up and the estimated “off blocks” time, that is, the time when the aircraft will leave the gate, was revised to 07:20.
In the cockpit, the first officer sat down in the right seat with the lead ground engineer remaining in the left seat. The overseas engineer moved to the galley in the centre of the cabin. The captain and the other engineer exited via the airstairs.
The aircraft was being loaded with cargo via an aircraft pallet loader positioned under the forward cargo door on the right side of the aircraft. There were four members of the loading team: one was loading the cargo into the plane, one operating the “Tarmac Transfer Vehicle” at the rear of the pallet, one was supervising and helping to load the cargo onto the vehicle. The fourth was sent to open the rear cargo doors.
The report does not mention the weather but presumably it was good as the captain did the walk around. Then he returned to the flight deck with the dispatcher and a ground technician who was also a part of the ground engineering team. The technician reported to the lead ground engineer that the walk-round inspection was complete. He then took a seat in the forward galley where he could watch the progress on the flight deck.
The lead ground engineer in the cockpit was using his laptop to work throiugh the Nose Landing Gear status messages related to the known issues. They weren’t critical and had already been confirmed as Acceptable Deferred Defects, which meant that they could be dealt with at a later date, for example with other, scheduled maintenance. The ground engineering team simply needed to carry out the appropriate Dispatch Deviation Guide procedure and clear the maintenance messages.
This procedure is a basic test which requires the engineers to apply hydraulic pressure and then cycle the cockpit landing gear selection, that is, take the gear lever from down to up and then down again.
Obviously the problem with this is that the landing gear would retract and then extend again, which isn’t something you want to do on the ground. To get around this, each gear has a downlock, which enables you to lock the gear in the down position by inserting a pin into a hollow cylindrical hole. Now you can cycle the gear lever without actually pulling the landing gear up.
The lead engineer asked the lead mechanic and another mechanic to fit the landing gear locking pins. He also told them to attach the ground communications headset to the external connection in the nose landing gear bay.
The two mechanics collected the five landing gear locking pins and went to the nose landing gear to fit the first one. The lead mechanic wasn’t quite tall enough to reach the locking pin hole without steps but the other man was, so he asked the second mechanic to fit the locking pin, pointing to the location of the hole. Then they made their way to the right main landing gear.
On the way, the second mechanic spoke to one of the loading team who was standing on the pallet loader, letting him know that they were going to apply hydraulic power to the aircraft. This can cause the aircraft to move slightly, so the mechanic warned the man that he needed to stand clear of the aircraft and lower the pallet loader to keep it away from the cargo door.
Meanwhile, the lead mechanic picked up a set of steps and placed two of the downlock pins on the right main landing gear and another two on the left landing gear. His task complete, he returned to the flight deck and told the flight engineer that the pins were all fitted. Then both mechanics returned to the nose landing gear, where the lead mechanic plugged in the headset and put it on.
He heard the lead engineer asking him to confirm that the landing gear pins were fitted and he said yes, they were. The second mechanic stepped clear from the aircraft and stopped by some nearby vehicles to watch.
The lead engineer had the appropriate section of the Aircraft Maintenance Manual open on his laptop and so, following the procedure, he applied hydraulic pressure. Then, again following procedure, he asked the lead mechanic to verify that the locking pins were in place and that the loading team were clear of the aircraft.
The lead mechanic glanced at all of the landing gears: all five warning flags on the downlock pins were clearly visible. All members of the loading team seemed to be clear but he bent down to look under the loading platform just to make sure there were no feet visible there. Everything seemed as it should be, so he confirmed to the lead engineer in the cockpit that the pins were fitted and that the pallet loader was clear of personnel.
The lead engineer pressed the LOCK OVERRIDE button and selected the landing gear lever to UP.
The nose landing gear retracted and the nose of the Dreamliner crashed to the ground.
— JACDEC (@JacdecNew) June 18, 2021
The nose of the aircraft crushed the articulated arm of a ground power unit, destroying the cable arm. The lower forward fuselage, nose landing gear doors and both engine cowlings struck the ground and were damaged. The left-side door connected to the airstairs was ripped off of its hinges as the aircraft lurched forwards, leaving the door hanging from electrical cables.
One of the ground loading team who was on the pallet loader was struck by the cargo door as it dropped. Inside the cockpit, the lead engineer and the first officer were thrown forward. Three personnel in the cabin and galley fell to the floor.
During the recovery operations, investigators found that the nose landing gear downlock pin had not been placed into the correct hole. It had been placed into a very similar hole next to the downlock, the nose landing gear apex pin bore.
This isn’t the first time this has happened. In 2018, another operator suffered an almost identical accident when during maintenance, the downlock pin was placed into the nose landing gear apex pin bore and the nose lever gear was moved to the UP position, leading to the nose landing gear retracting. As a result of this accident, Boeing released a service bulletin for installing an insert into the apex pin bore in order to stop the downlocking pin being inserted into the wrong hole. In January 2020, the FAA made this service bulletin mandatory as an Airworthiness Directive for all relevant Boeing jets, allowing for a compliance period of 36 months.
Obviously, this particular aircraft had not yet had the insert placed in the apex pin bore, although British Airways have stated that they are now expediting the procedure on their remaining Dreamliners.
The final report is still in progress at the British AAIB. Thanks to Mendel who spotted this special bulletin.