Module 11C.10, 11C.11, 11C.13 — B3 light aeroplanes: fuel, hydraulic power and landing gear

B3 levels

Sub-module	B3 level
11.10(a) Fuel system layout, tanks, supply	1
11.10(b) Cross-feed/transfer, refuelling/defuelling	1
11.10(c) Fuel indication and warnings	1
11.11(a) Hydraulic system description	2
11.11(b) Pressure generation, control, indication, servicing	2
11.13 Landing gear (construction, tyres, systems, tail protection)	2

Part 1 — Fuel systems (level 1)

Fuel grades

• AVGAS 100LL — blue; UL91 and other unleaded grades only where approved; MOGAS only with an approval (vapour lock, ethanol content restrictions).
• Jet A-1 must never be put into a spark-ignition engine (detonation). Diesel/compression-ignition piston engines (e.g. Jet-A-burning engines) are placarded accordingly.
• Placards at every filler: grade and capacity.

Layout and tanks

Layout	Features
Gravity feed (high wing)	Tanks above the engine; selector LEFT/RIGHT/BOTH/OFF; fuel flows by gravity to the carburettor
Pump feed (low wing)	Engine-driven pump plus electric boost (auxiliary) pump for start, take-off, landing and tank changes
Tanks	Integral (wet wing), rigid aluminium, bladder, or a single fuselage tank (some light/microlight-derived types)

Each tank has a filler cap (seal check), vent (must be clear — a blocked vent starves the engine and can collapse tanks), sump drain, and finger strainer at the outlet.

Supply

• Fuel selector valve — detents and placards; leak-tight; correct positions.
• Gascolator (strainer) — lowest point; traps water/sediment; drained pre-flight; bowl cleaned at inspections.
• Primer for starting; fuel lines (aluminium tube, fire-resistant hoses forward of the firewall).

Handling

• Cross-feed/transfer — on single-engine aircraft, by selecting tanks; some have transfer pumps from auxiliary tanks.
• Refuelling: bond aircraft to the fuel source before opening the filler; no smoking/flames; correct grade; after refuelling wait, then drain sumps and check for water.
• Defuelling via drains or defuel points into bonded, clean containers.

Indication

Float and variable-resistor quantity senders (most common), capacitance on some types, sight/direct-reading gauges; low-fuel warning; fuel pressure gauge or fuel flow on injected engines. Calibrate gauges after replacing senders (unusable fuel marking).

Key fact: Drain fuel sumps and the gascolator after refuelling and before flight — water sinks to the lowest point and stops the engine.

Part 2 — Hydraulic power (level 2)

Typical uses on B3 aircraft

Wheel brakes (the most common hydraulic system), and on some retractable or high-performance types landing gear and flaps.

System description

• Fluid: mineral-based hydraulic fluid (red, MIL-PRF-5606) with nitrile seals — never mix with other fluid types (e.g. phosphate ester or automotive brake fluid).
• Brake system: each pedal has a master cylinder with a small integral reservoir (or a common reservoir); lines to the caliper; parking brake valve traps pressure.
• Power pack (retractable types): electric motor + reversible gear pump + reservoir + check/relief valves + pressure switch.
• Filters, relief valves, actuators, selector valves as required.
• Accumulators are rare on B3 aircraft.

Pressure generation and control

• Manual (master cylinders, hand pump), electric (power pack), or mechanical (engine-driven pump on some).
• Pressure control by relief valves and pressure switches (power pack motor stops when pressure is reached).

Indication, warnings and servicing

• Gear position lights and power-pack motor running light; brake pedal feel is the main "indication" for brakes.
• Servicing: top up reservoirs with the specified fluid; bleed brakes from the caliper bleeder upwards (pressure-bleeding) to remove air (spongy pedal); check for leaks and hose deterioration.

Key fact: A spongy brake pedal usually means air in the system — bleed the brakes with the correct fluid.