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NTSB's findings
Thursday, March 25, 1999
The National Transportation Safety Board issued findings yesterday in its investigation of USAir Flight 427, a twin-engine Boeing 737-300 that crashed in a Hopewell ravine at 7:03 p.m. Sept. 8, 1994. Among them:
1. The pilots had proper certificates, were qualified and had received the training prescribed by federal regulations. There was no evidence of any pre-existing medical or behavioral conditions that might have adversely affected the pilots' performance during the flight.
2. The airplane was equipped, maintained and operated in accordance with applicable federal regulations.
3. All of the plane's doors were closed and locked at impact.
4. The plane didn't experience an in-flight fire, bomb, explosion or structural failure.
5. Neither a midair collision nor atmospheric phenomena, such as a bird striking the plane or turbulence, were involved in the accident.
6. Although the plane encountered turbulence from a preceding flight, Delta Flight 1083, the wake vortices - tight coils of air that spin off the wingtips of a plane - alone could not have caused the accident.
7. At about 7:03 p.m., the plane's rudder deflected rapidly to the left as far as it could go and stayed there.
8. First Officer Charles Emmett III was at the controls during the early stages of the incident. "Although it is likely both pilots manipulated the flight controls later in the accident sequence, it is unlikely that the pilots simultaneously manipulated the controls [possibly opposing each other] during the critical period in which the airplane yawed and rolled to the left."
9. No data support a scenario in which the pilots applied and held a full left rudder until the plane struck the ground more than 20 seconds later.
10. Analysis of the cockpit voice recorder, safety board computer simulation and other data "shows they are consistent with a rudder reversal most likely caused by a jam" of a hydraulically powered device that controls the rudder.
11. The pilots couldn't have assessed the flight control problem and then devised and executed the appropriate recovery procedure for a rudder reversal under the circumstances of the flight - its relatively slow air speed of 218 mph and its altitude of about 6,000 feet.
12. The pilots recognized the plane's predicament "in a timely manner" and took immediate action to attempt a recovery.
13. Training and piloting techniques developed as a result of the accident show it is possible to counteract an uncommanded deflection of the rudder.
14. It is possible that the device that controls the rudder could jam and, without leaving any obvious physical evidence that crash investigators could later find, move opposite to the direction commanded by the pilot.
15. When completed, the rudder system design changes to the Boeing 737 "should preclude the rudder reversal failure mode that most likely occurred" on Flight 427.
16. Rudder design changes to Boeing 737-NG series airplanes and the proposed installation of upgraded mechanisms don't eliminate the possibility of other potential failures and malfunctions in the Boeing 737 rudder system that could lead to a loss of control.
17. A completely independent backup rudder actuation system is needed for the Boeing 737, despite significant improvements already made in the system's design.
18. The Boeing 737 rudder system had proper certificates from the Federal Aviation Administration but doesn't have a reliable independent backup system.
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B737s - (NG)
