The Australian Transport Safety Bureau (ATSB) says failure to remove two of five landing gear downlock pins were the cause of an incident which saw a Qantas flight return to Sydney because its landing gear failed to retract.
The pins, which are marked with 'Remove before flight' tags, weren't identified while the aircraft was being towed to its gate or during any pre-flight inspections.
Failure to comply with the instructions to remove before flight, the wheels of the Boeing 787 aircraft could not retract once the aircraft had taken off.
The incident happened on June 21 and involved a Qantas Boeing 787-9 departing Sydney for Perth with 106 passengers and 13 crew onboard.
During the initial climb, when the flight crew went to raise the aircraft's landing gear, they received a warning indicating that neither main landing gear had retracted to the "up and locked" position.
Actioning the aircraft's electronic checklist did not resolve the issue.
The flight crew then selected the landing gear lever to down, resulting in a positive gear extension indication, and the aircraft was returned to Sydney for what the report calls an "uneventful landing".
Subsequent inspections identified that two of the aircraft's five landing gear downlock pins had not been removed after it had been towed to the domestic terminal aircraft bay in preparation for the flight.
"Pins are inserted into the nose and main landing gear when the aircraft is on the ground to prevent inadvertent gear retraction during maintenance or towing," ATSB Director Transport Safety Stuart Macleod explained.
"In this case two of the pins - one of the two for each main landing gear - had not been removed after towing and prior to the flight. In addition, subsequent pre-flight inspections by the flight and dispatch crew did not identify that the pins remained in place prior to departure."
Attached to each pin was a red 'remove before flight' streamer. One streamer on each main landing gear was visible in CCTV footage of the aircraft being towed to its bay prior to the flight.
The pins attached to these two streamers were removed before departure, while the second gear pin on each main landing gear was missed. The missed gear pin streamers may have been stuck on the gear, from a combination of grime and the recent wet and windy conditions.
Post-incident inspection found all four main gear pins' streamers to be in place, but dull and frayed. Their condition prior to the flight could not be conclusively determined.
"'Remove before flight' streamers are visual reminders to remove covers and lockout devices prior to flight, but can be subject to varying environmental conditions that can reduce their visibility," Macleod said.
"Expectation can also affect your ability to identify these warning devices. If you are not expecting to see a 'remove before flight' streamer, you are significantly less likely to detect one that is present.
"The same principle can also prevent the discovery of damaged and/or missing components."
The 787 has five landing gear pin locations: one in its nose gear, and two in each of its main landing gear, whereas other types in the Qantas fleet such as the A330 and 737 have three pins: One in the nose gear, and just one in each of the main landing gears.
The two members of the tow crew who had removed three of the five gear pins - one from the nose gear, and one each from the left and right main landing gear - had not towed a 787 prior to this event.
Qantas says it has since made changes to its procedures and has made sure all of its staff are aware that the Boeing 787 has five 'Remove before flight' tags, while other aircraft in the Qantas fleet only have three.
