At what NP percentage does the DEC receive the overspeed signal and shut off fuel?

At what NP percentage does the DEC receive the overspeed signal and shut off fuel?

• A. 120% NP
• B. 100% NP
• C. 110% NP
• D. 130% NP

Answer: (A)

The key idea is how the engine’s overspeed protection works. The DEC (digital engine controller) constantly monitors rotor speed, indicated as NP. When NP hits the established overspeed limit, the DEC automatically cuts fuel to the engine to stop acceleration and prevent damage. In this system, that limit is 120% NP, so reaching 120% triggers the fuel shutoff. Normal operation sits at 100% NP, and while 110% NP is high, it’s still below the protective threshold, whereas 130% NP would exceed the safe limit and would trigger protective actions sooner or indicate a more severe condition. Once fuel is shut off, the engine decelerates back below the limit, and normal operation can be reestablished through the appropriate restart procedure.

The key idea is how the engine’s overspeed protection works. The DEC (digital engine controller) constantly monitors rotor speed, indicated as NP. When NP hits the established overspeed limit, the DEC automatically cuts fuel to the engine to stop acceleration and prevent damage. In this system, that limit is 120% NP, so reaching 120% triggers the fuel shutoff. Normal operation sits at 100% NP, and while 110% NP is high, it’s still below the protective threshold, whereas 130% NP would exceed the safe limit and would trigger protective actions sooner or indicate a more severe condition. Once fuel is shut off, the engine decelerates back below the limit, and normal operation can be reestablished through the appropriate restart procedure.