FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsMedium
A helicopter is equipped with a hydraulic servo (boost) system for the flight controls. If this hydraulic system fails in flight, what change should the pilot expect in the flight controls?
- AThe collective will automatically lock in its last position
- BThe controls will move freely with virtually no resistance
- CThe controls will become impossible to move at all
- DThe controls will become significantly heavier, requiring more physical effort
Show answer & explanationAnswer & explanation
Correct answer: D. The controls will become significantly heavier, requiring more physical effort
Hydraulic servos reduce the aerodynamic feedback forces from the rotor system that the pilot would otherwise feel through the cyclic and collective. If hydraulic pressure is lost, control inputs are still mechanically connected to the rotor, but the pilot must overcome full aerodynamic forces directly, making the controls noticeably heavier and requiring more effort and larger control movements.
Why the other options are wrong
- A. There is no automatic lock; the pilot must continue manually flying with heavier controls.
- B. The opposite occurs; without hydraulic assistance, forces increase, not decrease.
- C. Controls remain mechanically connected and movable, just heavier, not frozen.
Hydraulic Servo (Boost) System
A system using engine/transmission-driven hydraulic pressure to reduce the aerodynamic feedback forces a pilot feels through the flight controls.
- Reduces cyclic/collective control forces from rotor feedback
- Pump is typically driven by the main rotor gearbox
- Accumulators may provide brief pressure after pump failure
- Failure results in heavier, but still functional, manual controls
Memory trick: Hydraulics are power steering — lose them, and the wheel (cyclic) gets heavy.