737 Perturbations

From:         jsteele@AZStarNet.com (Jerry Steele)
Organization: Arizona Daily Star - AZSTARNET
Date:         08 Feb 96 03:21:07 
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A recent announcement in the newswires by the Seattle times  states that
some U.S. airlines have begun to voluntarily change the way they fly Boeing
737s duringlanding approaches to give pilots a better chance of countering
potential uncontrolled movements of the aircraft's rudder as well as
training for flying 737's inverted.

The flight change involves pilots flying 737s slightly faster as the
aircraft descends toward landing. That would better ailerons, to offset
any severe, inadvertent rudder swings.

The 737 has fewer safeguards against inadvertent rudder hard-overs than
do other models.  The 737 has one large rudder controlled by a single
power control unit, or PCU.

The Boeing 727 and 747 models use a split rudder in which two rudder
sections are controlled separately by two PCUs. Thus, a rogue command
issued by one unit can be offset by the proper operation of the other
unit.

Boeing 757s, 767s and 777s use a single rudder controlled by multiple
PCUs, another way to minimize danger caused by a rogue signal issued by
one of the control units.

McDonnell Douglas jetliners use a device called a "limiter" that physically
prevents the rudder from extreme deflections in flight.

Concern about the potential for a rudder swing at low altitudes, when
there may be only a few seconds to make the proper recovery maneuvers,
led the pilots' group to call for special AEROBATIC training for 737pilots.
Such training would complement the approach speed change some airlines
are now embracing, thegroup contends.