Enhanced Boeing 737 Rudder System
The modification retains key features of the current, highly reliable system while adding elements designed to improve redundancy -- an aerospace design principle in which duplicate systems are used to prevent overall failure if one part is damaged. Primary changes affect the Power Control Unit (PCU) located in the airplane's tail; this mechanism controls the rudder's movement. The current PCU with one dual concentric valve will be replaced by a system with two independent valves, shown here in blue and yellow, with two independent "input" arms. Also, hydraulic pressure sensors in the new system will monitor both halves of the actuator; if abnormal pressures are sensed, the standby rudder system will activate automatically.
The 737 is among the world's safest airplanes, with a safety record twice as good as the overall jet fleet. This workhorse twinjet has completed more than 296 million hours of flight with an enviable record of reliability; today, a 737 takes off or lands somewhere in the world every 4.6 seconds.