Which value defines the NP overspeed threshold used to trigger DEC shutoff?

Which value defines the NP overspeed threshold used to trigger DEC shutoff?

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

Answer: (B)

Rotor speed protection is about keeping the rotor from spinning beyond what the system and airframe can safely handle. NP is the rotor speed expressed as a percentage of its normal, nominal speed. The DEC, or engine control, watches NP and will shut off fuel flow if the rotor starts to overspeed to prevent damage. The designated overspeed threshold for triggering that shutoff is 120% NP. This value sits above normal operating ranges so the system can tolerate brief spikes during aggressive maneuvers or gusts, yet it’s low enough to stop an unsafe rise before the rotor and engine are compromised. At 100% NP you’re in normal operation; 110% NP is elevated but not yet the protective limit; 130% NP would push past the designed protection window and increase risk. So 120% NP is the chosen threshold that provides timely protection while allowing for legitimate transient excursions.

Rotor speed protection is about keeping the rotor from spinning beyond what the system and airframe can safely handle. NP is the rotor speed expressed as a percentage of its normal, nominal speed. The DEC, or engine control, watches NP and will shut off fuel flow if the rotor starts to overspeed to prevent damage.

The designated overspeed threshold for triggering that shutoff is 120% NP. This value sits above normal operating ranges so the system can tolerate brief spikes during aggressive maneuvers or gusts, yet it’s low enough to stop an unsafe rise before the rotor and engine are compromised. At 100% NP you’re in normal operation; 110% NP is elevated but not yet the protective limit; 130% NP would push past the designed protection window and increase risk. So 120% NP is the chosen threshold that provides timely protection while allowing for legitimate transient excursions.