Fuel Systems
Crash-resistant (self-sealing) tanks and breakaway couplings, boost pumps and crossfeed, and capacitance quantity.
Fuel systems, summary notes
- Fuel is held in tanks (often CRASH-RESISTANT, self-sealing bladder tanks with breakaway couplings to prevent post-crash fire); boost pumps deliver fuel under positive pressure to the engine(s).
- A crossfeed lets either engine draw from either tank on twins; tanks are vented, have water drains at their low points, and fuel is filtered.
- Fuel QUANTITY is measured by capacitance probes; fuel flow, pressure and low-level/low-pressure warnings are provided.
- Crash-resistant fuel systems (CRFS), flexible bladder cells, self-sealing breakaway valves and frangible fittings, are a major helicopter safety feature to prevent fuel-fed fires in a survivable crash.
- Refuel/defuel and bonding/earthing for static control follow the same rules as fixed-wing.
- ⚠ Exam trap: helicopters emphasise CRASH-RESISTANT fuel systems (self-sealing bladder tanks + breakaway couplings) to prevent post-impact fire; fuel quantity is by capacitance probes, and crossfeed balances a twin.
What features make a helicopter fuel system 'crash-resistant', and why does it matter?
A crash-resistant fuel system uses flexible, self-sealing bladder tanks that resist tearing, plus breakaway (frangible) couplings and self-sealing valves at every connection so lines separate cleanly and seal rather than spilling fuel. This prevents fuel spraying onto hot or sparking components in an otherwise-survivable crash, dramatically reducing the risk of a post-impact fire, historically a major cause of helicopter accident fatalities.
Fuel systems concept map
Fuel Systems
Fuel systems quiz
Fuel Systems, quiz
1. Helicopter fuel tanks are often
Crash-resistant self-sealing bladder cellsRigid glass tanksOpen containers2. Breakaway (frangible) couplings in a crash-resistant fuel system
Separate cleanly and self-seal in a crashWeld shutAre non-structural3. Fuel quantity is measured by
Capacitance probesFloat switches onlyA dipstick in flight4. Boost pumps are fitted to
Deliver fuel under positive pressure and prevent vapour lockCool the cabin by circulating fuel through a heat exchanger in the environmental systemCharge the battery from the pump generator whenever the engine driven pumps are running5. On a twin, a crossfeed allows
Either engine to draw from either tankOnly the left engine to runFuel jettison only6. Fuel tanks are vented to
Keep the ullage at ambient pressureIncrease pressureStore extra fuel7. The main purpose of a crash-resistant fuel system is to
Prevent a post-impact fuel-fed fireIncrease rangeCool the engine8. Water is removed from fuel by
Draining the tank low points before flightAdding more fuelVenting air