Landing gear, wheels and brakes

Gear is either conventional (two mains and a tailwheel) or tricycle (two mains and a nosewheel), and fixed or retractable. Shocks are taken by spring steel legs, rubber bungees, or most often an oleo-pneumatic strut: oil is forced through an orifice to soak up the landing, and compressed nitrogen or dry air holds the aircraft up.

To service a strut: release the air, push it to the position the manual gives, fill with the right fluid to the level shown, bleed out trapped air, then inflate with nitrogen or dry air until the strut shows the extension the chart gives for the aircraft's weight.

Retractable gear

Retraction is hydraulic, electric or both. Down-locks and up-locks hold the gear; a squat switch (weight-on-wheels or air-ground switch) stops the gear being raised on the ground; a warning horn sounds if the throttle is closed with the gear up; and an emergency extension (a hand crank, free fall, or a bottle of compressed gas) lowers it if the normal system fails. Nosewheels usually have a shimmy damper, and are centered as they retract so they fit the wheel well.

Wheels and tires

• Check tire pressure cold; many larger aircraft use nitrogen, which doesn't support a fire and holds pressure better.
• Inflate tires on a removed wheel in a safety cage, and deflate before taking a split wheel apart; many manuals say deflate before removing it from the axle.
• Tubeless wheels have fusible plugs that melt and let the air out if hot brakes overheat the wheel, before it can burst.
• Look for cuts, bulges, flat spots, tread worn past limits and damage near the bead.

Brakes

Most aircraft use disc brakes, single or multiple disc. Wear is checked by the manual's method, often a wear pin that shrinks into the housing as the linings wear. A spongy brake pedal means air in the lines: bleed the brakes, from the bottom up or top down as the manual says. Larger aircraft add anti-skid, which releases a wheel's brake when it starts to skid.