ATPL Landing Gear Questions

The purpose of the torque links (torque arms) fitted to an oleo-pneumatic landing gear leg is to:

• Prevent the lower, sliding part of the gear leg from rotating relative to the fixed upper cylinder
• Transfer braking torque from the wheel to the axle
• Position the wheels correctly just before touchdown
• Prevent shimmy of the nose wheel specifically

Explanation: Torque links connect the lower sliding piston of an oleo-pneumatic gear leg to its fixed upper cylinder, allowing the leg to compress and extend freely while preventing the lower part - and the wheel/axle it carries - from rotating around the leg's axis, keeping the wheel correctly aligned.

Landing Gear - Torque Links

During full dynamic (aquaplaning) hydroplaning, the effective coefficient of friction between tyre and runway is generally close to:

• 0.0
• 0.5
• 0.1
• 1.0

Explanation: In full dynamic hydroplaning, a wedge of water lifts the tyre completely clear of the runway surface, leaving essentially no direct tyre-to-runway contact to generate friction. Braking and directional control become almost entirely ineffective, which is why hydroplaning is treated as such a serious hazard on a wet or contaminated runway.

Landing Gear - Hydroplaning

An underinflated tyre operated on a dry runway tends to:

• Increase wear on the tyre's shoulders (the outer edges of the tread)
• Increase wear concentrated on the tyre's crown (centre of the tread)
• Reduce the tyre's operating temperature
• Increase the tyre's hydroplaning speed

Explanation: An underinflated tyre bulges more at the sidewalls under load, causing the tread's outer shoulders to bear a disproportionate share of the contact-patch load and wear faster than the centre - the opposite of the crown wear characteristic of an overinflated tyre. Under-inflation also raises tyre operating temperature and reduces, rather than increases, the speed at which some forms of hydroplaning occur.

Landing Gear - Tyre Inflation and Wear

A landing gear leg is considered truly 'locked' in the down position when:

• It is mechanically secured by an over-centre locking mechanism, independent of hydraulic pressure
• The gear-down indicator light is illuminated
• The actuating cylinder has simply reached the end of its travel
• It has physically reached the fully extended position

Explanation: True mechanical locking relies on an over-centre linkage (a down-lock) that holds the gear extended by its own geometry, not by sustained hydraulic pressure - this is what keeps the gear safely down even if hydraulic pressure is later lost. An indicator light, a cylinder reaching its travel limit, or the leg simply reaching the down position are each just indications or contributing steps, not the locking mechanism itself.

Landing Gear - Down-Lock Mechanism