Module 11C.4–11C.6 — B3 light aeroplanes: heating and ventilation, instruments and avionics, electrical power

B3 levels for these sub-modules

Sub-module	B3 level
11.4(e) Heating and ventilation (the only part of 11.4 for B3)	1
11.5.1 Instrument systems	2
11.5.2 Avionics systems	1
11.6 Electrical power	3

Remember B3 privileges: avionics work only where simple tests prove serviceability and no troubleshooting is needed (66.A.20) — but electrical power is level 3, so you must understand and troubleshoot the electrical system.

11.4(e) Heating and ventilation (level 1)

• Exhaust shroud (muff) heater: ram air heated around the exhaust muffler → heater valve (push-pull "CABIN HEAT") → cabin and windscreen defrost outlets; surplus dumped overboard.
• Carbon monoxide hazard: cracks in the muffler/exhaust inside the shroud let CO into the cabin; inspect exhaust systems at each scheduled inspection (and per ADs for some mufflers), fit a CO detector (spot card or electronic).
• Ventilation: fresh-air scoops/eyeball vents, opening windows, NACA inlets; cabin exhaust outlets.
• Electric heaters (ground) and combustion heaters are rare on B3 aircraft.

Key fact: The biggest maintenance risk of an exhaust-shroud cabin heater is carbon monoxide from a cracked exhaust.

11.5.1 Instrument systems (level 2)

Pitot-static

• ASI (pitot + static) with colour arcs: white (flap operating range, V_S0 to V_FE), green (normal operating, V_S1 to V_NO), yellow (caution, V_NO to V_NE), red line (V_NE). Arc positions must match the AFM — check after instrument change.
• Altimeter (static, aneroid capsules, subscale setting) and VSI (static, metered leak).
• Alternate static source in the cabin → altimeter and ASI read slightly high.
• Pitot-static leak test after disturbance; correct line routing and drains.

Gyroscopic instruments

• Attitude indicator and heading indicator — usually vacuum-driven (suction 4.5–5.5 inHg) or electric.
• Turn coordinator (electric, gyro canted about 30°) or turn-and-slip indicator (rate gyro, horizontal axis) with slip ball.
• Heading indicator drift — reset to the compass.

Compass

Direct-reading compass: deviation card after a compass swing, compensator screws; avoid steel tools/magnetic items near it; variation, turning and acceleration errors.

Stall warning and AoA

Reed horn (pneumatic) or vane switch with horn/light; AoA indicators fitted as modifications on some aircraft.

Glass cockpit and engine indications

• Light-aircraft EFIS/integrated displays with AHRS and ADC; engine monitors (EGT/CHT for each cylinder, fuel flow).
• Indications of other systems: fuel quantity, oil pressure/temperature, ammeter/voltmeter, suction, annunciators.