Which SOV fails in the open position?

Which SOV fails in the open position?

• A. Cowl Anti-Ice SOV
• B. Pack SOV
• C. Engine Start SOV
• D. Isolation SOV

Answer: (A)

Bleed-air control valves have defined failure modes, and the one that would cause a problem if it stuck open is the valve feeding the cowl anti-ice system. When this valve is commanded off, it should close to stop bleed air from reaching the cowl anti-ice ducts. If it fails open, bleed air would continue to flow to the cowl anti-ice system even when anti-ice is not needed. That means the anti-ice system would stay on by itself, wasting bleed air, increasing fuel burn, and potentially causing unnecessary thermal stress in the cowl or unexpected icing protection activity. The other valves (packs, engine-start bleed, and isolation) either don’t create the same persistent undesired operation when they fail open, or their open-fail condition is less likely to produce a continuously active, uncommanded system in normal operations. That’s why the cowl anti-ice valve is the correct choice for a failure mode that presents an open-position fault.

Bleed-air control valves have defined failure modes, and the one that would cause a problem if it stuck open is the valve feeding the cowl anti-ice system. When this valve is commanded off, it should close to stop bleed air from reaching the cowl anti-ice ducts. If it fails open, bleed air would continue to flow to the cowl anti-ice system even when anti-ice is not needed. That means the anti-ice system would stay on by itself, wasting bleed air, increasing fuel burn, and potentially causing unnecessary thermal stress in the cowl or unexpected icing protection activity.

The other valves (packs, engine-start bleed, and isolation) either don’t create the same persistent undesired operation when they fail open, or their open-fail condition is less likely to produce a continuously active, uncommanded system in normal operations. That’s why the cowl anti-ice valve is the correct choice for a failure mode that presents an open-position fault.