A FADEC overspeed safety feature will shut down an engine at what RPM, plus or minus what tolerance, and which rotor is involved?

• A. 429 RPM ± 4 RPM, N2
• B. 425 RPM ± 2 RPM, N1
• C. 500 RPM ± 5 RPM, N2
• D. 450 RPM ± 3 RPM, N2

Answer: (A)

Overspeed protection is there to prevent the high-speed turbine rotor from exceeding safe limits, which could damage the engine and rotor drivetrain. In this case, the FADEC is set to shut the engine down when the N2 spool reaches about 429 RPM, with a tight tolerance of plus or minus 4 RPM. The N2 rotor is the power-turbine spool that ultimately drives the main rotor through the reduction gearbox, so protecting N2 from overspeed directly guards the rotor system. This precise threshold and tight tolerance ensure the system responds quickly to an overspeed condition while avoiding false trips from minor sensor noise.