Module 11B.12–11B.13 — Piston aeroplanes: ice and rain protection, landing gear

Scope and levels

Item	A2	B1.2
11.12(a) Ice formation, classification, detection	1	3
11.12(b) De-icing: electrical, hot air, pneumatic, chemical; probe/drain heating	1	3
11.12(c) Anti-icing systems	—	—
11.12(d) Wipers	1	3
11.12(e) Rain repellent	—	—
11.13(a)(b)(d) Landing gear construction, tyres, systems, tail protection	2	3
11.13(c) Air–ground sensing	—	—

Part 1 — Ice and rain protection (ATA 30)

Ice formation and classification

• Needs visible moisture and surface temperature at or below 0 °C; most likely between 0 °C and about −15 °C.
• Rime (small droplets, instant freezing, white/brittle), clear/glaze (large droplets, slow freezing near 0 °C, hard, heavy, spreads aft — most dangerous), mixed, and frost (sublimation; must be removed before flight).
• Piston aircraft also suffer induction (carburettor) icing — a Module 16 topic, but remember it can occur well above 0 °C in humid air.
• Certification: aircraft approved for flight into known icing (FIKI) carry full protection; others may have only partial systems (e.g. "non-hazard" TKS or pitot heat) and must avoid icing.

Detection

Mainly visual: ice on the windscreen wiper arm/edges, wing leading edges (ice inspection light at night), ice probe/rod visible from the cockpit; some aircraft have electronic ice detectors.

De-icing systems (B1.2 level 3)

System	How it works	Maintenance
Pneumatic boots (wings, tail, struts)	Air from the pressure side of the engine-driven pneumatic pump (dry air pumps) inflates boot tubes via a timer and distribution/flow-control valves; between cycles boots are held flat by vacuum	Clean, inspect for cracks/cuts/ozone damage, cold-patch repairs, conductive coating; check inflation sequence and pressure gauge/indicator light
Electrical propeller de-icing	Heater elements bonded to blade roots; power via brush block and slip rings; timer cycles heating between blades/propellers; ammeter shows current	Check brushes, slip rings, heater resistance, ammeter readings in each cycle
Fluid (TKS)	Glycol-based fluid pumped through porous leading-edge panels, propeller slinger rings and windscreen spray bar	Fluid level, filter, panel porosity (blocked panels), pump function, approved fluid only
Hot air	Not common on pistons (some heated windscreen/inlet designs via exhaust heat)
Electrical heating of probes and drains	Pitot heat, heated stall-warning vane/lift detector, heated fuel vents on some aircraft, heated static ports	Check heater current (ammeter) or warmth (carefully — very hot on the ground); "pitot heat" annunciators

Windscreen

• Electrically heated windscreen panels or hot-plate (bolt-on heated glass panel in front of the pilot) on FIKI aircraft; defroster airflow from the cabin heater on all aircraft.

Wipers

• Electric wiper motor and arm on some piston twins; never run dry; check blade condition, arm tension, park position.
• Many light aircraft have no wipers — rely on propeller slipstream.

Key fact: Pneumatic de-ice boots on piston twins are inflated from the pressure (outlet) side of the engine-driven dry air pump and held flat by vacuum from the suction side.

Part 2 — Landing gear (ATA 32)

11.13(a) Construction and shock absorption

Type	Features
Spring steel / composite legs	Flat spring leg (e.g. Cessna main gear) — simple, absorbs energy by flexing; no damping, so bounces
Oleo-pneumatic struts	Nitrogen/air spring + oil damping through an orifice/metering pin; nose gear on many singles, main gear on twins; servicing by extension vs pressure, fill with fluid when compressed
Rubber discs / bungee cords	Older types and tail-wheel aircraft; bungee cords have colour-coded manufacture dates and limited life
Tail-wheel	Steerable via springs/chains from the rudder; locks for take-off on some types
Tricycle with nose wheel	Nose strut with shimmy damper and torque links

• Tyres: tube-type or tubeless; ply rating/load rating; inflation pressure per the AMM, checked cold; creep marks (white painted alignment marks across tyre and rim) show if the tyre has slipped on the rim (tube-type — valve damage risk).
• Wheels: split-type, tie bolts torqued in sequence; bearings cleaned, inspected and repacked with the specified grease.

11.13(b) Systems

Retraction and extension

• Electro-hydraulic power pack (most common), electro-mechanical (motor, gearbox, push-pull tubes — e.g. some Beechcraft/Mooney) or manual (hand lever — older Mooney).
• Uplocks/downlocks: over-centre linkages, hook locks; gear doors sequenced mechanically or hydraulically.
• Squat (safety) switch on a main gear leg prevents gear retraction on the ground.
• Emergency extension: free-fall (release hydraulic pressure via an emergency valve; gear drops by gravity and airflow, often assisted by springs), hand crank (electro-mechanical systems), hand pump or CO₂ blow-down bottle.
• Automatic gear extension (airspeed-sensing) on some Piper models — check pitot pressure line and switch adjustment.

Indications and warnings

• Three green lights = down and locked; amber/red in transit or unsafe; mechanical indicators/mirrors on some types.
• Gear warning horn when throttle (manifold pressure) is reduced below a set value or flaps lowered with gear not down and locked.
• Gear retraction test on jacks (functional/operational check, emergency extension test) at intervals — gear swing.

Wheels and brakes

• Single-disc brakes (e.g. Cleveland-type): disc attached to the wheel (or fixed to the axle in some designs) with floating caliper and linings; wear limit by lining thickness or disc thickness.
• Master cylinders on the rudder pedals (toe brakes) — independent left/right brake systems with their own reservoirs; parking brake valve traps pressure.
• Bleeding brakes (pressure bleed from the caliper upwards); check for spongy pedals (air), leaks, overheated discs (blue tint), warped discs.
• Antiskid and autobrake are generally not fitted on light piston aircraft.

Steering

• Direct steering through rudder pedals via push-pull rods/springs to the nose gear, differential braking with a castering nose wheel, or tail-wheel steering springs.
• Towing: observe the turn limits (marked stops) — over-turning the nose wheel when towing damages steering stops/linkages; disconnect steering links if required.

11.13(d) Tail protection

Tail skids/bumpers protect the tail on aircraft prone to tail strikes; inspect for wear and attachment cracks, and inspect the rear fuselage after any strike.