Boeing 727 Flight Master

RUDDER LOAD LIMITER

The hydraulic pressure to the lower rudder has three options, it will be 800 psi when the flaps are UP, 2400 psi when the flaps are DOWN, or it will be zero when there is no hydraulic pressure.

The pressure controller that determines the output pressure is spring-loaded to the 2400 psi position and requires 3000 psi pressure to force it to the 800 psi output position. This is accomplished by the use of a solenoid valve.

The diagram below shows the power from the RUDDER LOAD LIMITER circuit breaker through a flap UP/DOWN switch, to a solenoid valve. When the flaps are UP, power is supplied to the valve and the valve opens. This, in turn, ports 3000 psi hydraulic pressure to the pressure controller and forces it to the 800 psi position.

The abnormal procedure calls for the pulling of the RUDDER LOAD LIMITER circuit breaker in the event of certain malfunctions. This action will remove power from the solenoid valve, and it is spring-loaded closed. When it closes, 3000 psi pressure is removed from the controller and it then is spring-loaded to the 2400 psi position.

FLIGHT CONTROLS

1 .        How do you arm the auto speedbrake?

The speedbrake lever is moved up and slightly aft.

2.         What causes the deployment of the auto speedbrakes?

Wheel spinup of 60 knots occurring on both main gears or left strut compression.

3.         Are you able to operate the ground spoilers in flight? If not, why?

No.  A hydraulic bypass valve operated by left strut extension at liftoff prevents the deployment of the ground spoilers in flight.

4.         What is the purpose of the rudder load limiter?

To reduce pressure to the lower rudder when the flaps are up.

5.         What does the RUDDER LOAD LIMITER light indicate?

It indicates a disagreement of hydraulic pressure to the lower rudder for the selected flap position.

6.         During loss of electrical power to the system, does the rudder load limiter unit fail to high or low rudder pressure?

The system fails to the high pressure mode.

7.         What procedure do you follow if the RUDDER LOAD LIMITER light illuminates?

First, refer to your company’s alternate procedures.  It will probably be

similar to the following:  If the flaps are up, avoid large or abrupt rudder inputs. If the flaps are extended, pull the rudder limiter control C/B. If the light remains on, limit the landing crosswind to 19 knots.

8.         With external power or APU powering the airplane, flaps are up and there is no System “A” hydraulic pressure.  Should the RUDDER LOAD LIMITER light be on or off and why?

Yes. The light should be on because anytime you don’t have electrical or System “A” hydraulic pressure, the system will fail in the high mode causing the RUDDER LOAD LIMITER light to illuminate.