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Report: Wrongly installed landing gear actuator causes loss of hydraulic system on Boeing 747-400
11 October 2015
Flight track (AAIB)

Flight track (AAIB)

An incorrectly installed landing gear actuator on a Boeing 747-400 caused a loss of hydraulic pressure and a return to land at London-Gatwick Airport, according to an AAIB report.

On 29 December 2014, a Virgin Atlantic Airways Boeing 747-400 aircraft departed from London Gatwick Airport for a scheduled flight to Las Vegas. Following retraction of the landing gear after takeoff, low quantity and pressure warnings occurred on hydraulic system 4, due to a hydraulic fluid leak. The required checklists were completed and the aircraft returned to land at London Gatwick Airport. As the landing gear extended during the approach, the right wing landing gear struck the gear door, preventing the gear leg from fully deploying. The crew carried out a go-around and, following a period of troubleshooting and associated preparation, a non-normal landing was successfully completed.

It was subsequently determined that the hydraulic retract actuator on the right wing landing gear had been incorrectly installed. This is an uncommon maintenance task. There was incomplete guidance for the maintenance crew of how to operate the specialist tools required by the Aircraft Maintenance Manual  (AMM). Also, several of these  specialist tools were not found. Ultimately the actuator was installed upside down.  The significance of this maintenance error was that the hydraulic fluid ports on the actuator were now transposed, with the port at the head end of actuator facing upwards. The AMM did not require the gear to be fully cycled following maintenance. Consequently, the insufficient clearance between the hydraulic port and the top of the landing gear bay, when the gear was in the retracted position, was not identified until the first time the gear was retracted fully during the incident flight the following morning. The force exerted on the hydraulic port as the gear retracted, caused it to distort and release hydraulic fluid at the full system pressure of 3,000 psi. This rapidly depleted the reserve of hydraulic fluid in system 4, generating a low quantity and then low pressure warning in the flight deck.

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