Investigation Summary
The aircraft departed San Francisco at approximately 14:00 local time. At 14:13, while climbing through 800 feet, the number 4 (outer right) engine's third-stage turbine disc disintegrated. The resulting uncontained failure sent high-velocity debris through the wing, rupturing the outboard reserve fuel tank and igniting a massive fire. The combination of the explosion and intense heat caused the engine and the outer 25 feet of the right wing to separate from the airframe. Captain Charles Kimes took control from the First Officer and managed to stabilize the aircraft despite the loss of a significant portion of the right wing's lifting surface. A passenger, William Richmond, captured the burning wing and the moment of structural failure on 8mm film. The crew utilized emergency procedures to lower the landing gear and successfully touched down at Travis Air Force Base 34 minutes after takeoff. The investigation by the Civil Aeronautics Board (CAB) revealed that the engine had been overhauled just 39 flight hours before the accident. The failure was caused by a loss of operating clearance between the turbine disc and the sealing ring, attributed to the use of improper tools, worn parts, and an inspector signing off on work that had not been physically inspected.
Final Conclusions
The Civil Aeronautics Board determined the probable cause was the failure of the third-stage turbine disc due to a transient loss of operating clearance. This loss of clearance was the result of improper turbine rotor positioning during assembly, the use of serviceable but worn parts, and a design clearance that was less than predicted. Maintenance human factors were central to the accident, specifically the failure of quality control personnel to verify the assembly work.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Pratt & Whitney JT3D-3B Engine
The number 4 engine suffered a catastrophic disintegration of the third-stage turbine disc due to improper assembly clearance.
Right Wing Structure
Approximately 25 feet of the outboard wing separated due to the force of the engine explosion and subsequent fuel fire.
Emergency Landing Gear Extension
The crew had to use emergency means to lower the landing gear for the touchdown at Travis AFB.
Interesting Facts
- 01The number 4 engine fell through the roof of a cabinet shop in San Bruno, penetrating a concrete wall.
- 02A passenger captured the entire sequence of the wing burning and falling off on 8mm color film.
- 03The aircraft, N761PA 'Clipper Friendship', was repaired and returned to service, later appearing in the 1966 film 'Dimension 5'.
- 04The engine involved had been overhauled only 39 flight hours prior to the failure.
- 05A replacement aircraft sent to Travis AFB to pick up the passengers suffered a nose gear collapse on the runway before they could board.
Safety Actions & Advisories
Maintenance Inspection Oversight
The investigation highlighted the critical need for inspectors to physically verify turbine rotor positioning rather than 'signing off' based on procedural assumptions.