FAA Finalizes 737 Rudder Mandate

WASHINGTON—The Department of
Transportation`s Federal Aviation
Administration (FAA) today published a
final rule requiring Boeing 737
operators to install a newly designed
rudder control system, and to make
other changes to the aircraft to
accommodate the new system.

Today’s final rule airworthiness
directive (AD) affects about 2,000 U.S.-
registered airplanes at an estimated
total cost of approximately $364
million. There are about 4,500 737s in
the worldwide fleet. The AD was first
published for public comment on Nov.
13, 2001.

The new design, which is being
finalized by Boeing, will increase the
overall safety of the 737 by
simplifying the rudder system and
eliminating a range of failure
possibilities. The redesign also will
make it unnecessary to continue
existing flight crew operating
procedures and associated training,
which were designed to address failure
possibilities unique to the existing
737 rudder system.

The enhanced rudder control system will
feature new or modified components
including an aft torque tube, hydraulic
actuators, associated control rods and
additional wiring throughout the
aircraft to support a system fault
indicator in the cockpit. The system
will incorporate two separate inputs,
each of which can be overridden by the
pilots, to two separate servo valves on
the main rudder power control unit
(PCU). Input to the backup standby PCU
also will have an override mechanism.
Operators must install the new system
within six years.


From mid-1999 to mid-2000, a government-
industry 737 Flight Control Engineering
Test and Evaluation Board (ETEB)
conducted a top-to-bottom analysis of
the Boeing 737 rudder system, including
possible ways the 737 rudder system
could malfunction.

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The FAA already has taken many safety
actions on the 737 rudder system. Two
years ago, the agency mandated a
simplified procedure for handling a
jammed or restricted rudder and began
training 737 pilots on the new methods.
The FAA also made several maintenance
changes to reduce the possibility of
undetected failures. 

The FAA had previously ordered other
design changes that increased the
safety level of the 737 rudder system.
All U.S.-registered 737s have improved
rudder power control units, a more
reliable yaw damper mechanism and a
hydraulic pressure reducer that gives
pilots a greater margin of control if
the rudder makes unintended movements.


A copy of the airworthiness directive
is available at:
http://www.access.gpo.gov/su_docs/aces/a
ces140.html

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