When does the DEC receive the NP overspeed signal and shut off the fuel?

When does the DEC receive the NP overspeed signal and shut off the fuel?

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

Answer: (A)

NP overload protection relies on a clear speed limit for the rotor. The Digital Engine Control constantly watches NP, the rotor speed expressed as a percentage of its maximum. When NP hits the overspeed threshold of 120%, the DEC automatically commands fuel shutoff to the affected engine to prevent turbine and blade damage. This is a rapid, built-in safety response that works even if the pilot is holding a different throttle setting, so the engine cannot continue to accelerate beyond safe limits. After fuel is cut, the engine decelerates, and normal fuel control can resume once NP drops below the safe range. The other values are outside the designed protective action: normal operation is around 100%, a higher but non-threshold value like 110% won’t trigger the shutoff, and a much higher value such as 130% would exceed the protection envelope and lead to different protective behavior.

NP overload protection relies on a clear speed limit for the rotor. The Digital Engine Control constantly watches NP, the rotor speed expressed as a percentage of its maximum. When NP hits the overspeed threshold of 120%, the DEC automatically commands fuel shutoff to the affected engine to prevent turbine and blade damage. This is a rapid, built-in safety response that works even if the pilot is holding a different throttle setting, so the engine cannot continue to accelerate beyond safe limits. After fuel is cut, the engine decelerates, and normal fuel control can resume once NP drops below the safe range. The other values are outside the designed protective action: normal operation is around 100%, a higher but non-threshold value like 110% won’t trigger the shutoff, and a much higher value such as 130% would exceed the protection envelope and lead to different protective behavior.