Incident Overview
During a night departure, a Boeing 747 experienced a birdstrike while the landing gear was extended. The strike sheared an attach rod on a landing gear door, preventing the door from closing. The flight crew and ground personnel did not detect the birdstrike due to the aircraft's physical size and the nighttime conditions.
Flight Crew Response
After retracting the landing gear, the flight crew noticed a vibration. While the vibration appeared related to the landing gear, all indications showed the gear had retracted normally. The crew considered that additional noise and vibration during gear extension could have masked other issues. Sterile cockpit procedures limited non-emergency communications during critical phases, so the first indication of abnormality came when the cabin services manager contacted the flight deck.
Once the vibration's nature and location were established, the crew used all available resources, consulting maintenance operational control and cabin crew, to systematically isolate systems that could generate the vibration. Although they could not identify the source, they determined the vibration was constant and the aircraft otherwise performed normally. With no abnormal flight deck indications or relevant checklist, the crew exercised professional judgment to continue the flight.
Technical Details
The Boeing 747 landing gear system uses hydraulics and attach rods to extend and retract the gear and associated doors. Proximity switch sensors on the gear and hydraulically operated doors provide indications of normal and abnormal operation. Small doors attached directly to the gear by rods lack proximity sensors, as they normally open and close with the gear.
Investigation revealed the sheared attach rod and evidence of a birdstrike, consistent with the aircraft having struck a bird during departure with the gear extended. The damaged rod prevented the L3 door from closing, causing residual turbulence and vibration. The absence of a proximity sensor meant the crew was unaware the door remained open.