USAir Flight 427 Rudder Hardover leads to Fatal Crash! On September 8, 1994, USAir Flight 427, a Boeing 737-3B7 registered as N513AU, was en route from Chicago O’Hare to Palm Beach with a scheduled stop at Pittsburgh International Airport. While on approach to Runway 28R at Pittsburgh, the aircraft abruptly lost control and crashed in Hopewell Township, Pennsylvania, killing all 132 occupants. The investigation, conducted by the National Transportation Safety Board (NTSB), concluded that the aircraft's rudder experienced an uncommanded hardover, leading to a loss of control. The event was initiated as Flight 427 encountered wake turbulence from a preceding Delta Air Lines Boeing 727 at approximately 6,000 feet. Shortly after, the aircraft’s rudder deflected fully to the left without pilot input. This rudder movement caused an uncontrollable left roll and rapid descent. The crew attempted corrective actions by rolling the control yoke right and pulling back on the elevators, but their actions exacerbated the situation by increasing the angle of attack, leading to an aerodynamic stall. The NTSB’s extensive investigation, lasting over four years, revealed that the rudder hardover was caused by a failure in the main rudder power control unit (PCU). The PCU’s servo valve was found to be susceptible to thermal shock, a condition where cold hydraulic components are suddenly exposed to heated hydraulic fluid. This failure could result in the rudder moving in the opposite direction of pilot command. Bench tests confirmed that this failure mechanism, though rare, could occur under specific conditions. As a result of the investigation, Boeing redesigned the rudder control system on all 737 models, adding redundancy to prevent similar failures. The Federal Aviation Administration (FAA) mandated modifications to existing aircraft and required enhanced flight data recording capabilities to capture rudder pedal inputs. No further rudder reversal incidents have been recorded since these modifications were implemented. Subscribe to our Aviation Safety Newsletter NOW and get the hot stuff free and without delay: https://lnkd.in/eGZqhPHR! Visit https://AEROTHRIVE.com for professional training courses, audits and solutions in aviation safety, compliance, quality and operations!
