NTSB revises report, says rudder probably caused '91 air crash

WASHINGTON (CNN) -- Ten years after a United Airlines 737 crashed in a field near Colorado Springs, Colorado -- killing all 25 aboard -- federal accident investigators have revised their findings and now conclude that the crash was caused by a jammed rudder mechanism.

Investigators said the rudder forced the plane to turn one direction when the pilots commanded it to go the opposite direction.

This is the second time the National Transportation Safety Board has officially closed the book on United Flight 585, but the first time it has established a probable cause for the accident.

About two years after the March 3, 1991, crash, the NTSB wrote in a report that it "could not identify conclusive evidence to explain the loss of" the aircraft, but suggested a possible malfunction of the plane's control system or unusually severe weather. The accident was one of four jetliner accidents in the NTSB's 34-year history that remained unsolved.

But investigators took a fresh look at the crash following two similar incidents involving Boeing 737s. On September 8, 1994, USAir Flight 427 crashed near Pittsburgh, Pennsylvania, killing 132 people. On June 9, 1996, an Eastwind Airlines Boeing 737-200 experienced control difficulties while on approach to Richmond, Virginia. The Eastwind crew was able to maintain control and landed the aircraft safely.

Based on all three occurrences and on tests of Boeing 737s, the board issued a final report on USAir Flight 427, citing a malfunction in the plane's rudder system as the most likely cause of all three events.

The board on Tuesday announced it had accepted a revised report on United Flight 585 citing the same probable cause as that of USAir Flight 427. Since the problem in Colorado occurred less than 1,000 feet above the ground, the pilots had very little time to react and recover from the problem, the board said.

Since the crashes of United 585 and USAir 427, the board said, Boeing has redesigned new power control unit servo valves for all 737s operating in this country and has retrofitted older planes.