A technician is servicing a pneumatic emergency landing gear extension system's air storage bottle and must select the correct charging gas. Why is dry nitrogen specified rather than shop compressed air for this system?
- ANitrogen expands more predictably under Boyle's Law than compressed air
- BNitrogen is inert and moisture-free, reducing corrosion and fire hazard risk
- CNitrogen provides greater pressure per cubic foot at the same bottle volume
- DNitrogen is required because compressed air cannot achieve high storage pressures
Show answer & explanationAnswer & explanation
Correct answer: B. Nitrogen is inert and moisture-free, reducing corrosion and fire hazard risk
Dry nitrogen is used in aircraft pneumatic systems because it is chemically inert (won't support combustion) and free of moisture, which prevents internal corrosion of system components and eliminates the risk of ice formation as gas expands and cools during use. Ordinary shop compressed air often contains moisture and is not filtered to aviation cleanliness standards.
Why the other options are wrong
- A. Boyle's Law applies equally to all gases; nitrogen doesn't behave more predictably than air under this law.
- C. Both gases can be compressed to similarly high pressures; nitrogen isn't chosen for pressure density advantages.
- D. Compressed air can be compressed to very high pressures just as nitrogen can; pressure capability is not the reason for the choice.
Nitrogen in Pneumatic Systems
Dry nitrogen gas is used to charge aircraft pneumatic systems and accumulators because it is inert and moisture-free, minimizing corrosion, ice formation, and fire risk compared to shop compressed air.
- Nitrogen does not support combustion
- Moisture-free gas prevents internal corrosion and ice during rapid expansion
- Shop compressed air is not used because of moisture and contamination content
Memory trick: Nitrogen = the 'dry, calm gas' that won't rust pipes or feed a fire.