Enhanced Boeing 737 Rudder System
Principal changes affect the Power Control Unit (PCU) located in the airplane's tail; this unit controls the rudder's movement. The enhanced system (shown here in blue and yellow) retains features of the current, highly reliable rudder system and adds elements to improve redundancy, an aerospace design principle in which duplicate systems are used to prevent overall failure if one part is damaged. The new enhanced PCU features two independent valves and dual input arms; the input arms incorporate spring overrides (shown in blue and yellow) that allow the system to operate normally if one portion of the system becomes jammed. Also, hydraulic pressure sensors in the new system will monitor both halves of the PCU; 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.