A birdstrike as it was departing San Francisco saw a Qantas operated Boeing 747-400ER continue its flight to Sydney with one of its left main landing gear door down, causing abnormal vibrations during the flight.

The Australian Transport Safety Bureau(ATSB) says the event occurred on 6 October 2016, and involved VH-OEH.

In its final report, the investigator says an undetected birdstrike during the aircraft's departure "sheared a landing gear door strut resulting in the door not closing." That, in-turn, led to turbulent airflow and "an abnormal vibration in the area of the left over-wing door".

The crew, however, received no indications in the cockpit of any abnormalities and did not have any procedures to manage the observed vibrations. After liaising with Qantas's maintenance operational control centre and unsuccessfully troubleshooting a number of potential causes of the vibration, the crew opted to continue the flight as the aircraft appeared to be operating normally.

After landing, engineers identified a protruding gear door seal, and a closer examination found that the rod that attaches to the landing gear door had been sheared.

"Despite the door not being closed during the flight, there was no additional wear or damage. The attach rod was replaced and the aircraft returned to normal service, with no further vibration or noise reported," the ATSB says.

While the incident yielded no significant safety issues, the investigator says that it highlights that even with complex systems and technology for diagnosing faults, flight crew may experience situations where they have to rely on their own professional judgement.

"In this case, the flight crew utilised the support of both on-ground maintenance personnel and cabin crew to methodically troubleshoot the source of the vibration and assess that the flight could be safely continued to the destination airport," it adds.

Source: Cirium Dashboard