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B733, vicinity Pittsburg PA USA, 1994

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On 8 September 1994, a US Air Boeing 737-300 crashed near Pittsburg USA following loss of control attributed to a rudder malfunction.
Event Details
When September 1994
Actual or Potential
Event Type
Airworthiness, Loss of Control
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft BOEING 737-300
Operator US Airways
Domicile United States
Type of Flight Public Transport (Passenger)
Origin Chicago/O'Hare International Airport
Intended Destination Pittsburgh
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Manoeuvring
Location - Airport
Airport vicinity Pittsburgh
Tag(s) Inadequate Airworthiness Procedures
Tag(s) Significant Systems or Systems Control Failure,
Extreme Bank
Tag(s) “Emergency” declaration
System(s) Flight Controls
Contributor(s) OEM Design fault,
Component Fault in service
Safety Net Mitigations
Stall Protection Available but ineffective
Damage or injury Yes
Aircraft damage Hull loss
Fatalities Most or all occupants (132)
Causal Factor Group(s)
Group(s) Aircraft Technical
Safety Recommendation(s)
Group(s) Aircraft Operation,
Aircraft Airworthiness
Investigation Type
Type Independent


On 8 September 1994, a US Air Boeing 737-300 crashed near Pittsburg USA following loss of control attributed to a rudder malfunction.


The following is the Executive Summary from the official National Transportation Safety Board (USA) (NTSB) report (AAR-99/01):

"On September 8, 1994, about 1903:23 eastern daylight time, USAir (now US Airways) flight 427, a Boeing 737-3B7 (737-300), N513AU, crashed while maneuvering to land at Pittsburgh International Airport, Pittsburgh, Pennsylvania. Flight 427 was operating under the provisions of 14 Code of Federal Regulations Part 121 as a scheduled domestic passenger flight from Chicago-O'Hare International Airport, Chicago, Illinois, to Pittsburgh. The flight departed about 1810, with 2 pilots, 3 flight attendants, and 127 passengers on board. The airplane entered an uncontrolled descent and impacted terrain near Aliquippa, Pennsylvania, about 6 miles northwest of the destination airport. All 132 people on board were killed, and the airplane was destroyed by impact forces and fire. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.

The National Transportation Safety Board determines that the probable cause of the USAir flight 427 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide. The safety issues in this report focused on Boeing 737 rudder malfunctions, including rudder reversals; the adequacy of the 737 rudder system design; unusual attitude training for air carrier pilots; and flight data recorder (FDR) parameters.

Safety recommendations concerning these issues were addressed to the Federal Aviation Administration (Federal Aviation Administration (FAA)). Also, as a result of this accident, the Safety Board issued a total of 22 safety recommendations to the FAA on October 18, 1996, and February 20, 1997, regarding operation of the 737 rudder system and unusual attitude recovery procedures. In addition, as a result of this accident and the United Airlines flight 585 accident (involving a 737-291) on March 3, 1991, the Safety Board issued three recommendations (one of which was designated “urgent”) to the FAA on February 22, 1995, regarding the need to increase the number of FDR parameters."

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Further Reading

For further information:

  • see the official NTSB Aircraft Accident Report: AAR-99/01