Aural Warnings: which statements are true about NR thresholds?

Aural Warnings: which statements are true about NR thresholds?

• A. They occur at NR <= 350 RPM only
• B. They occur at NR >= 380 RPM only
• C. They occur at NR <= 345 RPM and NR >= 380 RPM
• D. They occur at NR <= 300 RPM and NR >= 390 RPM

Answer: (C)

Aural warnings are triggered when rotor speed (NR) is outside the safe operating range, and this system uses two guardbands to catch both ends of that range. The numbers shown indicate warnings occur when NR is at or below 345 RPM or at or above 380 RPM. Between these values, from just above 345 up to just below 380, there’s no alert, meaning there’s a defined safe window. This design helps the pilot react to rotor speed that’s too low (risk of loss of lift) as well as rotor speed that’s too high (risk of overspeed damage). The other options don’t fit because they cover only one side or use incorrect thresholds, whereas the correct interpretation requires recognizing both low and high NR warning boundaries.

Aural warnings are triggered when rotor speed (NR) is outside the safe operating range, and this system uses two guardbands to catch both ends of that range. The numbers shown indicate warnings occur when NR is at or below 345 RPM or at or above 380 RPM. Between these values, from just above 345 up to just below 380, there’s no alert, meaning there’s a defined safe window. This design helps the pilot react to rotor speed that’s too low (risk of loss of lift) as well as rotor speed that’s too high (risk of overspeed damage). The other options don’t fit because they cover only one side or use incorrect thresholds, whereas the correct interpretation requires recognizing both low and high NR warning boundaries.