13.15, 13.18, 13.19 Ice and rain protection, pneumatic/vacuum and water/waste

Scope

All are in the B2L Airframe Systems block as well as B2.

• 13.15 Ice and rain (ATA 30): (a) ice formation, classification, detection — level 2; (b) de-icing: electrical, hot-air, pneumatic, chemical; probe and drain heating — level 3; (c) anti-icing: electrical, hot-air, chemical — level 2; (d) wipers — level 1; (e) rain repellent — level 1.
• 13.18 Pneumatic/vacuum (ATA 36) — level 2: layout; sources (engine/APU, compressors, reservoirs, ground supply); pressure control; distribution; indications; interfaces.
• 13.19 Water/waste (ATA 38) — level 2: water layout, supply, distribution, servicing and draining; toilet layout, flushing and servicing.

Ice formation and detection

• Ice forms when supercooled water droplets strike a surface at or below 0 °C. Rime (small droplets, white, brittle), clear/glaze (large droplets, hard, heavy, most dangerous), mixed; frost on parked aircraft.
• Effects: increased stall speed, reduced lift, increased drag and weight, control-surface jamming, blocked probes, engine damage from shed ice, antenna and radome icing (degraded radio).
• Ice detectors: vibrating-probe type (resonant frequency decreases as ice accretes; the probe then de-ices itself and counts cycles), optical detectors, and visual cues (ice-detector rod, windscreen wiper bolts, wing illumination at night). Detectors can automatically switch on wing and engine anti-ice on some aircraft.

Anti-icing versus de-icing

• Anti-icing prevents ice from forming — continuous heat (running wet or evaporative).
• De-icing removes ice after a thin layer has formed — cyclic.

Method	Anti-ice use	De-ice use
Hot air (bleed)	Wing/slat leading edges via piccolo tubes; engine intake cowl lips	—
Electrical	Windscreens, probes, drain masts, some propeller/rotor spinners	Propeller and rotor blade heater mats (cyclic), some leading edges on newer aircraft (heater blankets)
Pneumatic boots	—	Inflatable rubber boots on wing/tail leading edges of turboprops
Chemical (fluid)	Freezing-point depressant fluid weeping from porous panels (TKS-type)	Ground de-icing fluids; fluid on propellers

Pneumatic boots

• Inflated in sequence by regulated engine-bleed air through solenoid-operated distributor/timer valves; between cycles they are held down by vacuum from an ejector (venturi) to stay flat and streamlined.
• Inflation cycles (span-wise or chord-wise tubes, typically a few seconds each) crack the ice so the airflow removes it.
• Inspect for cuts, deterioration, bonding; use only approved conductive coatings and cleaners.

Electrical windshield heat (important B2 content)

• Laminated glass/acrylic with a conductive film (gold or tin-oxide) or embedded wires.
• Window heat control units regulate temperature using sensors (thermistors) laminated into the panel, with an independent overheat sensor; power is applied gradually to avoid thermal shock; side windows may be on a lower setting (anti-mist).
• Faults: delamination, arcing, sensor failure — window heat failure is an MEL item.

Probe and drain heating

• Pitot, static, TAT, AoA probes heated electrically; heaters monitored by current sensors → caution if a heater fails; often automatic on with engines running or in flight; probes are heated at low power on the ground on some types.
• Drain masts (waste-water) heated to prevent ice blocking them.