Investigation Summary
The accident occurred during a multi-leg cargo and mail flight from San Francisco to South Vietnam. Due to poor weather at Anchorage International Airport, the flight diverted to Elmendorf Air Force Base. During the arrival, the crew noted a technical issue with the No. 4 engine thrust reverser, adding to their workload. During taxi in freezing conditions, Captain Arthur Moen retracted the flaps to prevent ice accumulation in the flap tracks, a standard cold-weather procedure. While the First Officer had initially lowered them during the first reading of the taxi checklist, the subsequent retraction was not caught during the final pre-takeoff checks because the Pan Am checklist only listed the flap setting during the taxi phase, not the immediate pre-takeoff phase. The crew was also under significant time pressure; they had been given a 'void time' by Oceanic Control, meaning a failure to take off by 06:15 would result in a 45-minute delay. This pressure, combined with the distraction of navigating unfamiliar, slippery taxiways with a 'follow me' truck, led to the oversight. Although ATC originally cleared the flight for Runway 5, the crew requested Runway 23 because it offered a greater effective length. The Boeing 707 was equipped with a takeoff warning horn designed to sound if the throttles were advanced without flaps extended, but the system did not activate. In the cold Alaskan air, the engines produced sufficient thrust for takeoff at a lower throttle lever angle than the warning system's trigger point. Boeing had previously issued a Service Bulletin to lower this trigger point, but Pan Am's engineering department had incorrectly deemed it unnecessary for their fleet.
Final Conclusions
The NTSB determined the probable cause was an attempted takeoff with flaps retracted due to a combination of factors: an inadequate cockpit checklist that lacked a final flap verification, a warning system that failed to account for cold-weather thrust settings, and crew stress caused by an ATC-imposed deadline. The board also cited Pan Am's failure to implement Boeing Service Bulletin 2384. The investigation resulted in a mandatory Airworthiness Directive (AD) issued by the FAA on May 28, 1969, requiring the modification of the takeoff warning system on all Boeing 707s.
Photographic Evidence (1)
Video Analysis
A Deadly Mistake That Went Unnoticed | The Crash Of Pan Am Flight 799 — A detailed look at how a missing checklist item and a misconfigured warning system led to the loss of a Pan Am Boeing 707 in Anchorage.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Arthur Moen, aged 47.
First Officer
Johannes D. Markistein, aged 38.
Flight Engineer
James R. Skellenger, aged 31.
Systems & Failure Modes
Takeoff Warning System
A system designed to sound a horn if the throttles are advanced for takeoff while the flaps are not in a takeoff configuration. On N799PA, it was set to trigger at 42 degrees of thrust-lever advancement, which was not reached due to high engine performance in cold air.
Stick Shaker
A mechanical device that rapidly vibrates the control yoke to provide a tactile warning to the pilots that the aircraft is approaching an aerodynamic stall.
Wing Flaps
High-lift devices on the trailing edge of the wings. For the Boeing 707, these must be extended to a specific setting to provide enough lift for a safe takeoff at calculated speeds.
Interesting Facts
- 01The aircraft was a Boeing 707-321C named 'Clipper Racer'.
- 02The takeoff warning horn failed to sound because the thrust levers were not advanced far enough to trigger the sensor, despite producing takeoff thrust in the cold air.
- 03The 'lower flaps' item appeared on the taxi checklist but was absent from the pre-takeoff checklist.
- 04The crew was rushing to meet a 06:15 'void time' to avoid a 45-minute traffic delay.
- 05The right wing contacted the ground 94 feet left of the extended centerline.
Safety Actions & Advisories
FAA Airworthiness Directive 69-12-02
Issued May 28, 1969, making Boeing Service Bulletin 2384 mandatory, requiring the takeoff warning system throttle actuation point be reduced from 42 degrees to 25 degrees.
Checklist Revision
The NTSB recommended that air carrier checklists be reviewed to ensure critical items like flap settings are verified immediately prior to takeoff.