12.14 Helicopter landing gear (ATA 32)

Scope

Level 2 (A) and 3 (B1.3).

• 12.14(a) System description and operation: construction and shock absorbing; extension and retraction (normal and emergency); wheels, tyres, brakes; steering; skids; floats.
• 12.14(b) Sensors: indications and warnings; air–ground sensing.

Types of helicopter undercarriage

Type	Features	Typical use
Skids	Two longitudinal skid tubes joined to the fuselage by cross tubes (front and rear); shock absorbed by plastic bending of the cross tubes and elastic flexing; replaceable skid shoes/wear plates	Light and medium helicopters
Fixed wheels	Tricycle or tail-wheel layout with oleo struts	Medium helicopters
Retractable wheels	Hydraulic or electric retraction into sponsons/fuselage — reduced drag	Larger, faster helicopters
Floats	Fixed inflated floats or emergency pop-out floats packed on skids	Over-water operations

Skid gear notes:

• Cross tubes are designed to yield in a hard landing; after a heavy landing check the skid-tube splay/deflection against limits and inspect for cracks at the saddle clamps.
• Ground-handling wheels clip onto the skids to move the helicopter.
• Some skid gear has dampers (or a tuned design) because skid stiffness influences ground resonance.

Shock struts (oleo-pneumatic)

• A cylinder and piston containing hydraulic fluid and nitrogen (or dry air); landing energy compresses the gas (spring) while fluid forced through an orifice (often metered by a tapered pin) dissipates energy as heat.
• Servicing: deflate, fill with the specified fluid to the correct level with the strut fully compressed (or per the extension chart), then re-inflate with nitrogen to the correct extension or pressure.
• Strut extension and pressure affect ground resonance behaviour — incorrect servicing is a classic cause.