Boeing B-737-300 N513AU

Summary

On 8 September 1994 at about 23:03 local time, a Boeing B-737-300 registered N513AU, operated by Usair, was involved in an accident near Aliquippa, Pennsylvania, United States. 132 people were on board and 132 died. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

8 September 1994 at 23:03

Classification

Accident

Location

Aliquippa, Pennsylvania, United States

Coordinates

40.6104, -80.2506

Aircraft

Boeing B-737-300

Registration

N513AU

Category

Airplane

Engines

2

Operator

Usair

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Chicago → Pittsburg

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

DCA94MA076

132 people died.

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.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The airplane crashed while maneuvering to land at Pittsburgh International Airport. The airplane entered an uncontrolled descent and impacted terrain about 6 miles east of the airport. The airplane struck the ground at an angle of descent of about 80 degrees, in a slight roll to the left, and the airspeed was about 260 knots at impact. The investigation revealed that during the accident sequence, the airplane rudder deflected rapidly to the left and reached its left aerodynamic blowdown limit shortly thereafter. Examination of the rudder system revealed that it is possible, in the main rudder power control unit (PCU) of the airplane (as a result of some combination of tight clearances within the servo valve, thermal effects, particulate matter in the hydraulic fluid, or other unknown factors), the servo valve secondary slide could jam to the servo valve housing at a position offset from its neutral position without leaving any obvious physical evidence and that, combined with rudder pedal input, could have caused the rudder to move opposite to the direction commanded by a rudder pedal input. This condition of the PCU was also consistent with analysis of the cockpit voice recorder, computer simulation, and human performance data, including operational factors

Quoted verbatim from the NTSB record.