Rotor Brake Pressure in Flight

• Background
• Symptoms
• Emergency Procedure

Background

Many helicopters have a rotor brake to slow the rotors after landing and engine shut down. It brings the rotors to a stop quicker, allowing occupants to safely exit the helicopter sooner.

Rotor brakes are similar to disk brakes in cars. Hydraulic pressure is used to create friction on a disk, which effectively resists rotor motion and slows rotor speed.

A rotor brake is activated by pulling a lever in the cockpit, often mounted on the ceiling. At high speeds the rotor will naturally decelerate quickly, and the rotor brake risks excess heat and wear. Hence, the brake is not applied until the engines are off and the rotor speed has dropped below a certain threshold.

Very rarely, the brake may malfunction and pressurize in flight. It’s also possible an occupant could accidentally or intentionally pull the brake lever in flight. This requires the engine to provide more torque/power to maintain rotor speed. If brake pressure is too high, the engine will not be able to maintain the desired rotor speed and the rotor will slowdown.

Symptoms

Possible symptoms of a rotor brake pressuring follow.

• Many helicopters have a light in the cockpit which illuminates when rotor brake pressure is detected.
• Many helicopters provide an aural que when brake pressure is detected.
• Engine torque/power increase unexpectedly.
• Rotor speed decreases unexpectedly. This will only happen if the brake overpowers the engine’s ability to maintain rotor speed.
• The rotor brake lever is not fully stowed.

Emergency Procedure

If brake pressurization is detected in flight, the following steps may be followed.

1. Ensure the rotor brake lever is fully stowed. Passengers have been known to pull the brake lever.
2. Disable the hydraulic system used by the rotor brake. There may be more than one hydraulic system on the aircraft and a pilot should know which hydraulic system powers which components.
3. Be prepared for degradation in other systems using the disabled hydraulic system. This may reduce aircraft stability and/or the forces required to move the primary controls, among other things.
4. Stay within the potentially constrained flight envelope associated with the disabled hydraulic system. This often means flying below a reduced top speed.
5. Land as soon as practical.