USAir 427 – Pittsburgh Rudder Reversal
Date of Incident: September 8, 1994
Location: Hopewell Township, Pennsylvania, USA
🧭 What Happened
USAir Flight 427, a Boeing 737-3B7, crashed during approach to Pittsburgh International Airport. The aircraft experienced a rudder hardover — the rudder deflected fully in the opposite direction of pilot input — causing an unrecoverable roll and aerodynamic stall. All 132 onboard were killed. The crash led to a landmark investigation and major changes in rudder system design and upset recovery training.
✈️ Aircraft Details
Flight Number: US427 / USAIR 427
Aircraft Type: Boeing 737-3B7
Registration: N513AU
Route: Chicago O'Hare (ORD) → Pittsburgh (PIT) → Palm Beach (PBI)
Fatalities: 132 (127 passengers, 5 crew)
Survivors: 0
🔍 Key Factors
- Wake turbulence from Delta 1083 preceded rudder malfunction
- Rudder reversed due to jam in servo valve secondary slide
- Aircraft entered steep left roll and stalled
- Pilots pulled back on yoke, worsening stall due to sideslip
- Crash occurred 28 seconds after onset of upset
📆 Timeline of Events
- 22:10 UTC – Departure from Chicago O'Hare
- 23:02:53 UTC – Aircraft rolls out of left bank at 6,000 ft
- 23:03:01 UTC – Rudder reverses; aircraft yaws left
- 23:03:07 UTC – Stall begins; pitch reaches -20°
- 23:03:25 UTC – Impact near Aliquippa, PA
🎙️ Cockpit Voice & Flight Data
“Four-twenty-seven, emergency!” — Captain Germano
“God, no.” — First Officer Emmett
The CVR captured crew confusion, stick shaker activation, and final exclamations. The FDR showed full rudder deflection, increasing bank angle, and pitch down to 80°. The microphone remained keyed throughout the descent, broadcasting cockpit audio to ATC.
⚙️ Aircraft Systems & Failures
- Single rudder PCU design with dual servo valve
- Secondary valve jam caused primary valve overtravel
- Rudder deflected opposite to pilot input
- 737 lacked manual rudder backup
- Crossover speed too low to counter rudder with ailerons
🛡️ Aftermath and Reforms
- Longest NTSB investigation in history (4.5 years)
- Redesign of 737 rudder system to prevent reversals
- Upset Recovery Training Aid developed for pilots
- FAA issued airworthiness directives for rudder PCUs
- Crash helped solve United 585 and Eastwind 517 incidents
- Memorial erected near crash site in Hopewell Township