Gate 41

Things that look scary but have an explanation

What are those thumps and whirrs under the floor?

I heard a clunk and a whine below me. Is something falling off?

After takeoff the landing gear folds up into the belly to cut drag. Before landing it extends again. You hear hydraulic pumps, doors opening and the gear locking in place. The rumble on retraction is the wheels being braked so spinning tyres do not whip around inside the bay.

The gear usually comes down a few miles from the runway, often around 2,000 feet above the ground, though procedures vary by airline and aircraft.

Once down, mechanical over-centre locks hold each leg, and cockpit indications confirm "down and locked". If the hydraulics ever failed, there is an alternate method: the gear can drop under its own weight (free fall) and lock.

A little deeper

Large long-haul aircraft such as the 787 and A350 have six-wheel bogies on each main leg to spread the load on the runway. The shock strut is an oil-and-gas spring that absorbs landing energy.

Tyres are filled with nitrogen: dry, inert and less sensitive to temperature changes. Brakes are carbon or steel, and anti-skid systems stop wheels locking.

Honest limits: gear problems are rare and well-trained. Crews follow checklists and ground staff, fire services and ATC have procedures ready.

See it in Gate 41, in the outside view

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