What you should know about… Landing Gear Doors
Of the hundreds of structural parts and hundreds of moving parts on a commercial airplane, there are very few that are both structural and moving that also face the aerodynamic and mechanical-performance demands placed on landing gear doors. They must perform flawlessly under all flight conditions and meet a host of contingency requirements in the event of aircraft power loss or landing gear failure. To decrease drag in flight, undercarriages retract into the wings and fuselage with wheels flush with the surrounding surface or concealed behind flush-mounted doors.
Gravity extension in emergency
The landing gears and doors are moved by a set of actuating cylinders. For each door, a cylinder opens and closes the door. In nominal mode, the landing sequence is: open the doors of the landing gear boxes, extend the landing gears and close the doors. After taking off, the retraction sequence to be performed is: open the doors, retract the landing gears and close the doors.
The landing gears and landing gear doors are operated and controlled electrically and hydraulically. In abnormal operation, the landing gear can be extended by gravity. An Auxiliary Ground Door Opening System allows on-ground access to each landing gear bay for maintenance purposes. This system is electrically operated and controlled from GDO Panels.
No vibration or rattle during flight on an A350
The doors are hinged back-to-back in the center of an A350 fuselage and open only when the landing gear are retracted or deployed. On an aircraft, a perfectly shaped door would vibrate or rattle during flight. This would be a very distressing thing for passengers to hear. Engineers discovered that constantly changing air pressures as the aircraft changes altitude and airspeed cause the main landing gear door to change shape. Designers determined where and how these changes occurred and then used that data to optimize the design. A warped door is more difficult to close and latch, but the warp design provides built-in stress that keeps it from vibrating.
What if the landing gear doors don’t open before landing?
It is important to cover all the different situations that can occur on a flight.
- Normal operation: Doors open and close via hydraulic action, followed by deployment or retraction of the landing gear.
- Landing gear malfunction: Doors remain closed and locked in the event of inadvertent landing gear deployment.
- Door hydraulic power malfunction: Doors are pushed open by landing gear deployment in the event of loss of hydraulic power to the doors.
- Total hydraulic power malfunction: Doors withstand pressure of flight dynamics in the event that landing gear push the doors open by gravity and they remain open while in flight.
No landing gear doors on a B737
The B737 was built to be a short-haul, regional airliner with low ground separation. This allows ground staff working in small domestic airports to service and prepare the aircraft easily under the limitations of those airports in the 1960s. With such a design, Boeing deemed landing gear doors infeasible from a safety standpoint. Additionally, the complications surrounding the development of the landing gear bay doors as well as the added weight and maintenance considerations ultimately led Boeing to conceive a workaround. This is why the B737 model today still has no landing gear doors. Rubber seals surrounding the opening of each wheel well seal off the gap between the wheels and fuselage surface once the gear is retracted. This creates a protective barrier that prevents foreign objects, rain, and other elements from entering and potentially damaging the components inside.