National Transportation Safety Board
Investigation Update
USAir Flight 427

On Sept. 8, 1994, USAir flight 427, a Boeing 737-300, crashed
on approach to Pittsburgh, killing all 132 passengers and crew on board.

Status of Investigative Work

• The NTSB investigation into the crash of USAir flight 427 near Pittsburgh has been tough and challenging. It is the longest, and possibly most complex, aviation accident investigation in the NTSB's 31-year history.
• The NTSB expects to issue a final report, including a probable cause of the accident, in early 1999.
• Investigators (NTSB and parties with direct participation) have spent more than 100,000 hours on the investigation.
• The NTSB has found no evidence that the following were involved in the accident: criminal intent; engine reverse deployment; slat/flap extension; spoiler extension; cargo door, service door or entry door opening in flight; cargo shifting; electromagnetic interference; engine mount/pylon failure; floor beam failure; and bird strikes.
• The majority of NTSB's investigation this year has focused on aircraft systems, aircraft performance, human performance and sound spectrum analysis.
• Investigators have logged more than 6,000 hours performing scientific aircraft rudder tests to determine the impact of pilot inputs, hydraulic fluid contamination, yaw damper failure, rudder power control until failure, structural failure, electrical short circuits and effects of extreme temperatures.
• Information from more than 60 flight data recorders have been analyzed from 737 flights in which pilots reported uncommanded rolls.
• This summer investigators completed all planned tests and research in connection with the USAir 427 accident. Investigators are completing analyses of data from those tests.
• A special team of government and industry control system experts completed its review of NTSB's work to make sure safety issues have not been overlooked.

Recommendations Stemming from the Accident

• Since the accident, the NTSB has issued 20 safety recommendations focusing on flight data recorders, the 737's rudder and rudder control system and pilot training.
• The first three recommendations were issued to the FAA in February 1995, calling for expanded parameters on older 737s and all transport category aircraft.
• In October 1996, the NTSB issued 14 recommendations to the FAA urging a series of operational and design changes to the rudder system, and unusual attitude pilot training.
• In February 1997, the NTSB issued three additional recommendations to the FAA urging the expeditious installation of a redesigned main rudder power control unit on 737 aircraft; advising pilots of the potential for a reverse rudder response when a full or high-rate input is applied to rudder pedals; and develop operational procedures for flightcrews to recognize and recover from unusual attitudes and upsets caused by a reverse rudder response.
• NTSB has classified 13 of FAA responses to these recommendations "acceptable," seven have been classified "unacceptable."

Flight Data Recorders

• The investigation has been hampered by the accident aircraft's lack of a sophisticated flight data recorder (11 parameters). Crucial parameters missing -- and not required by the FAA at the time of the accident -- from Flight 427's flight data recorder include: pitch control surfaces positions, control wheel and lateral control surfaces positions, rudder pedal and yaw control surfaces positions, and lateral acceleration.
• The lack of a sophisticated flight data recorder (5 parameters) hampered the NTSB’s investigation of another 737 accident, the crash of United Airlines flight 585 in Colorado Springs on March 3, 1991 that claimed 25 lives.
• If these two 737s had enhanced flight data recorders, data from additional parameters would have allowed the NTSB to quickly identify any abnormal control surface movements, configuration changes or autopilot status that may have been involved in the loss of airplane control.
• In contrast, a sophisticated flight data recorder (98 parameters) on an ATR-72 that crashed in Roselawn, Ind. in 1994, killing 68, yielded a vast amount of valuable data. Within a week of the crash of American Eagle flight 4184, flight data enabled investigators to quickly focus on critical areas of the investigation. Comprehensive FDR data enabled the NTSB to issue urgent recommendations on the operation of that aircraft in icing conditions -- 8 days after the accident.

737 Statistics

• It's important that the NTSB find out what happened in Pittsburgh because the 737 is the world's most popular jet and has transported more than 5 billion people.
• 2,990 737s in service worldwide, operated by more than 270 airlines in more than 100 countries.
• 73 million flights by 737s over the past 30 years.
• 85 million flight hours.
• 800 737s are in the air worldwide at any given time.
• One 737 takes off every 6 seconds.

NTSB's Investigative Track Record

• Rarely has the NTSB failed to find out what caused an aviation accident.
• In its 31-year history, NTSB has investigated more than 110,000 aviation accidents. Some 350 of these have been major aviation accidents involving large jet aircraft and commuter turboprop aircraft.
• The NTSB has issued probable causes in more than 98% of all its major aviation accident investigations.
• Only four accidents remain unsolved, including the United Airlines 737 crash at Colorado Springs.
• Other unsolved major accidents are:
• Allegheny Airlines Convair 440, Bradford, Penn., January 6, 1969: 11 fatalities.
• Southern Airways DC-9, Huntington, WV, November 14, 1970: 75 fatalities including the Marshall University football team.
• Sierra Pacific Airlines Convair 340/440, Bishop, Calif., March 13, 1974: 36 fatalities including a David Wolper film crew.
• NTSB current major investigations in which the Board expects to issue probable causes:
• USAir 737, Pittsburgh, Sept. 8, 1994: 132 fatalities
• TWA 747, East Moriches, NY, July 17, 1996: 230 fatalities
• Federal Express MD-11, Newark, NJ, July 31, 1997: No fatalities
• Korean Air 747, Guam, Aug. 5, 1997: 227 fatalities

Revised: October 15, 1998