One of the most horrendous aviation disasters involved USAir Flight 427, which resulted in such a grisly scene that rescue workers were traumatized by its sheer horror. The crash site was so littered with “blood, body parts, and twisted metal that it was declared a biological hazard” (Melvin, 1994.) Investigators from the NTSB as well is the FAA were able to recover the black box from the flight, and set about the task of discovering what exactly happened to the flight. This paper will discuss the details of the flight, the number of passengers on board as well as fatalities, and the investigation of the disaster as well as its conclusions.
USAir Flight 427 took off on September 8, 1994, on a regularly scheduled trip from Chicago, Illinois to Pittsburgh, Pennsylvania. The flight consisted of two pilots, three flight attendants, and 127 passengers when it entered an uncontrolled descent and impacted terrain about 6 miles northwest of the destination airport (Aircraft Accident Report, 1994.) The flight crew had radioed while it was preparing to make a final turn before landing, and there was no indication that anything had gone wrong (Melvin.) Flight 427 crashed while approaching the airport, killing all 132 people aboard (Gabbay, 1995.) Seconds before crashing, the captain and copilot were heard to be screaming while the jet began spinning out of control, diving approximately one mile nose-first into a dense wooded area. The force of the crash had left the victims unrecognizable, with limbs hanging from trees and blood-smeared patches up to 200 yards from the point of impact (Kifner, 1994.) Everyone who was present at the scene of the crash was told to be vaccinated for hepatitis because of the threat that they had been in contact with contaminated blood. The area was cordoned off to prevent any media outlets and photographers from intruding into the area, but at least eight people were arrested for trying to sneak onto the crash site (Kifner, 1994.)
Initially, the NTSB felt that the probable cause of the accident involved a loss of control of the aircraft that resulted from the movement of the rudder surface to its blowdown limit (Aircraft Accident Report, 1994.) Most likely, the surface of the rudder was deflected in a path that was opposite from the one which was directed by the pilots because of the jamming of the central rudder power control unit servo secondary slide to the servo valve housing offset from its neutral position and over-travel of the primary slide (Aircraft Accident Report, 1994.) The report that was issued concentrated on malfunctions that were suspected of being common to the Boeing 737 that included reversals of the rudders, problems with the 737 design of the rudder system, uncommon attitude training for pilots of air carriers, and parameters of the flight data recorder.
There were several safety recommendations regarding the aforementioned issues that were brought to the attention of the FAA. In addition, because of the nature of this accident, the Safety Board released 22 recommendations to the FAA to reinforce safety of the Boeing 737 in particular. Specifically, the recommendations centered on the operation of the 737 rudder system as well as unusual attitude recovery procedures (Aircraft Accident Report, 1994.) After an extensive investigation of the crash which lasted over three years, the NTSB concluded that the most likely cause of the accident was an un-commanded full rudder deflection or rudder reversal that “placed the aircraft in flight regime from which recovery was not possible using known recovery procedures” (Investigation: USAir Flight 427, 2013.) In addition, the Board believed that another contributing factor causing the accident had been the failure of the manufacturer to sufficiently advise operators of these aircraft that there was a certain speed below which the aircraft’s lateral control authority was insufficient to counteract a full rudder deficit (Investigation: USAir Flight 427, 2013.)
The conclusions of the NTSB were ironic because immediately during the aftermath of the plane crash, one of the areas that were considered to be a primary focus was the possibility of a malfunction regarding the rudder system (Gabbay, 1995.) USAir itself had been warning pilots who were flying the Boeing 737s to be on the lookout for sudden movements of the rudder while planes were in flight. Because the rudder has the capacity to move a plane in either direction, any problem with its function threatens to completely alter the trajectory of any flight. The NTSB urged that all existing and future 737s have a reliably redundant rudder actuation system, and that an engineering test should be conducted in order to provide a failure analysis to identify potential failure modes, as well as several other safeguards to anticipate how the aircraft could be managed should such failures occur.