Boeing will have to revise the design of 737 rudder control system components, develop a cockpit display showing rudder position, and establish service life limits for certain rudder control parts if several proposals under study by the US National Transportation Safety Board (NTSB) are made compulsory. The aim is to eliminate any potential for loss of control from an uncommanded rudder hard over.
In September, the Federal Aviation Administration proposed nine airworthiness directives (AD) requiring changes in the 737 flight-control system (Flight International, 11-17 September). The most important changes would be to the rudder and its yaw-damper. Some of the NTSB's concerns are addressed by the ADs.
Investigators say that at certain air speeds, pilots may suffer uncommanded full rudder deflection and lose control of the 737. Operational changes may include making higher minimum airspeeds compulsory, an instruction which some operators already insist on implementing.
Boeing has decided to install a rudder limiter on the latest versions of its 737 to prevent unexpected rudder movement.
Source: Flight International
