Boeing expects to deliver the first production Next Generation 737 fitted with the enhanced rudder control system in January next year, around six months early.

The company says the programme is ahead of schedule following a smoother than expected development and flight-test effort, and expects to certificate the system in December. The revised system will be retrofitted to all Next Generation 737s from the second quarter of 2003 and be available for retrofit to 737 Classics from the third quarter. Flight tests of the revised system were completed in June on a Next Generation 737 and are due to begin later this month on a Classic aircraft.

The system was developed in the wake of two fatal accidents in 1991 and 1994. Both were judged to have been caused by large, uncommanded rudder deflections. The redesign also followed a government/industry 737 Flight Control Engineering Test and Evaluation Board review that found other possible failure modes which persisted, despite the mandated retrofit of a redesigned power control unit (PCU) and yaw damper system.

The enhanced system incorporates a different PCU design with two independent valves and actuator arms to meet US National Transportation Safety Board and Federal Aviation Administration requirements that eliminate danger from a "single failure or jam in the linkage aft of the torque tube".

Source: Flight International