This is not the first time the 737 has had rudder issues:
During the 90s, a series of rudder issues affected the 737
resulted in multiple incidents.
In two separate accidents
(United Airlines Flight 585 and USAir Flight 427),
pilots lost control of their aircraft due to a sudden and unexpected
rudder movement, the resulting cгashes kіlled everyone on board,
157 people in total. Similar rudder issues led to a temporary loss of
control on at least one other 737 flight before the cause of the
problem was ultimately identified.
The National Transportation Safety Board determined that the incidents
were the result of a design flaw that resulted in an un-commanded
movement of the aircraft's rudder.
The issues were resolved after the Federal Aviation Administration ordered modifications for all Boeing 737 aircraft in service.
In 2016, former NTSB investigator John Cox stated that time has proven the NTSB correct in its findings because no additional
rudder-reversal incidents have occurred since Boeing's redesign.
The NTSB was still investigating Flight 427 when the pilots of
Eastwind Airlines Flight 517 briefly lost control of their aircraft,
a 737-200, while flying from Trenton, New Jersey, to Richmond, Virginia. The aircraft experienced two episodes of rudder reversal
while on approach to land in Richmond.
Unlike the two prior incidents, the rudder issues on Flight 517 spontaneously resolved and the pilots were able to safely land
the aircraft.
The NTSB investigated the Eastwind incident, and incorporated information from both United Flight 585 and Eastwind Flight 517
into its ongoing investigation of the Flight 427
Because Eastwind Flight 517 had landed safely and the pilots of Flight 517 had survived, the NTSB was also able to perform tests on a plane that had experienced problems similar to the accident aircraft,
The captain told the NTSB in a post-accident interview that they had not encountered any turbulence during the flight, and that, during their landing descent, he felt the rudder "kick" or "bump" even though neither pilot had moved the rudder pedals.
When the plane abruptly rolled to the right, the captain applied left aileron and attempted to move the rudder, but the rudder pedal controls felt stiffer than normal and did not seem to respond to his input; when his flight control inputs did not immediately resolve the roll upset, he also advanced the throttle of the right engine in an
effort to compensate, saving all souls onboard.