FAA Aviation Mechanic Airframe (AMA)Fuel, Cabin and Ice Control SystemsHard
A technician is inspecting an onboard inert gas generation system (OBIGGS) installed to reduce the fire hazard in a transport-category aircraft's center wing fuel tank. How does this system reduce the flammability of the fuel tank ullage?
- AIt maintains a slight negative pressure in the tank to prevent vapor formation
- BIt circulates cooled bleed air to lower fuel vapor temperature below the flash point
- CIt adds fuel system icing inhibitor to suppress ignition of fuel vapors
- DIt injects nitrogen-enriched air produced by an air separation module to lower oxygen concentration
Show answer & explanationAnswer & explanation
Correct answer: D. It injects nitrogen-enriched air produced by an air separation module to lower oxygen concentration
OBIGGS uses an air separation module (ASM) to strip oxygen from bleed air, producing nitrogen-enriched air (NEA) that is injected into the fuel tank ullage, lowering oxygen concentration below the level needed to sustain combustion.
Why the other options are wrong
- A. OBIGGS does not rely on negative pressure to control flammability.
- B. Cooling vapor temperature is not how OBIGGS operates; it changes gas composition, not temperature.
- C. FSII prevents ice formation in fuel, unrelated to tank flammability reduction.
Onboard Inert Gas Generation System (OBIGGS)
A system that uses an air separation module to produce nitrogen-enriched air, which is injected into fuel tank ullage to reduce oxygen concentration and fire risk.
- Uses bleed air through an air separation module (ASM)
- Produces nitrogen-enriched air (NEA)
- Lowers oxygen content below flammability threshold in fuel tank ullage
Memory trick: OBIGGS suffocates the fire before it can even start, by starving it of oxygen.