Investigation Summary
The flight departed JFK at 19:14 EST into a region experiencing severe winter weather. The flight was chartered to pick up the Baltimore Colts in Buffalo after the aircraft originally earmarked to transport the team was grounded by a snowstorm in Detroit. As the aircraft climbed through 16,000 feet, the crew received a false overspeed warning because the iced-over pitot tubes were providing increasing pressure readings as the aircraft climbed, simulating high speed. Ten seconds later, the stick shaker activated, indicating an impending stall. The crew, confused by the conflicting data, pulled back on the control column, pitching the nose up to 30 degrees. This action induced a genuine deep stall. The aircraft entered a right-hand spin and descended at rates exceeding 15,000 feet per minute. During the descent, vertical acceleration reached +5 g, causing a large portion of the horizontal stabilizer to separate at approximately 3,500 feet. The aircraft struck the ground just 83 seconds after leaving its peak altitude of 24,800 feet.
Final Conclusions
The NTSB determined the probable cause was the loss of control because the flight crew failed to recognize and correct the aircraft's high angle of attack, low-speed stall, and descending spiral. The stall was precipitated by the crew's improper reaction to erroneous airspeed and Mach indications resulting from pitot head icing. A contributing factor was the crew's failure to activate the pitot head heaters prior to or during the flight. (NTSB/AAR-75-13, released August 13, 1975).
Video Analysis
Two crashes in one day! Ground this aircraft! Boeing 727 — A detailed look at the crash of Northwest Orient Airlines Flight 6231 and the instrument failures that led to a fatal stall.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
John B. Lagorio, age 35.
First Officer
Walter A. Zadra, age 32. Only 46 hours of his type experience were as a pilot; the remainder was as a flight engineer.
Second Officer
James F. Cox, age 33. Experience was as a Boeing 727 Flight Engineer.
Systems & Failure Modes
Pitot-Static System
Provides airspeed and altitude data; blockage of the pitot tubes by ice caused the airspeed indicators to show an increase in speed as the aircraft climbed, despite the actual speed decreasing.
Pitot Heat
Electrical heaters designed to prevent ice accumulation on the pitot probes; these were not activated by the crew.
Stick Shaker
A mechanical device that vibrates the control yoke to warn the pilot of an impending stall; the crew misinterpreted this as a high-speed buffet.
Interesting Facts
- 01The aircraft was a ferry flight intended to transport the Baltimore Colts football team from Buffalo.
- 02The flight was chartered because the original aircraft for the team was grounded by a snowstorm in Detroit.
- 03The crash occurred on the same day as TWA Flight 514, another Boeing 727 accident in the eastern U.S.
- 04The aircraft descended from 24,000 feet to ground level in only 83 seconds.
- 05The pitot tube heaters were found to be in the 'OFF' position at the time of the crash.
- 06The vertical acceleration during the spiral descent reached +5 g.
- 07The aircraft's Manufacturer Serial Number (MSN) was 20296/777 and it was manufactured in 1969.
Safety Actions & Advisories
Cockpit Design and Training Improvements
The investigation prompted changes in commercial pilot training regarding stall recognition and advancements in cockpit design to prevent similar instrument misinterpretations.