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Accident description
Last updated: 11 December 2017
Status:Final
Date:Thursday 29 May 1947
Time:19:05
Type:Silhouette image of generic DC4 model; specific model in this crash may look slightly different
Douglas DC-4
Operator:United Airlines
Registration: NC30046
C/n / msn: 18324
First flight: 1944
Total airframe hrs:5950
Crew:Fatalities: 2 / Occupants: 4
Passengers:Fatalities: 41 / Occupants: 44
Total:Fatalities: 43 / Occupants: 48
Airplane damage: Destroyed
Airplane fate: Written off (damaged beyond repair)
Location:New York-La Guardia Airport, NY (LGA) (   United States of America)
Crash site elevation: 7 m (23 feet) amsl
Phase: Takeoff (TOF)
Nature:Domestic Scheduled Passenger
Departure airport:New York-La Guardia Airport, NY (LGA/KLGA), United States of America
Destination airport:Cleveland Municipal Airport, OH (CLE/KCLE), United States of America
Flightnumber:UA521
Narrative:
A Douglas DC-4, operated by United Air Lines, was destroyed in an accident at New York-La Guardia Airport, New York, USA. Five of the 48 occupants survived the accident.
The DC-4, named "Mainliner Lake Tahoe", was ready for takeoff at 19:04 hours local time. The tower operator asked whether the flight wished to wait out a storm on the ground. The captain answered. "I'll take off." The tower then advised the flight: "Cleared for immediate takeoff, or hold; traffic on final approach north of Riker's Island." Flight 521 rolled onto runway 18, and accelerated for takeoff immediately. The captain applied back pressure to the control column but the controls felt heavy and the aircraft did not respond. The captain decided to discontinue takeoff.
About 1,000 feet from the south end of the runway he applied brakes, ordering the co-pilot at the same time to cut the engines. A ground-loop was attempted by heavy application of left brake. The aircraft, however, proceeded to roll straight ahead. Then, with both brakes locked it continued over the remainder of the runway, crashed through the fence at the airport boundary, and half-bounced, half-flew across the Grand Central Parkway. The aircraft finally came to rest immediately east of the Casey Jones School of Aeronautics, a distance of 800 feet from the end of runway 18 and 1,700 feet from the point at which brakes were first applied. It was almost immediate enveloped in flames.
Investigation revealed that the guts locks on the plane had been altered, permitting it to remain locked even after removal of the gust lock warning tape.

Probable Cause:

PROBABLE CAUSE: "The Board determines that the probable cause of this accident was either the failure of the pilot to release the gust lock before take-off, or his decision to discontinue the take-off because of apprehension resulting from rapid use of a short runway under a possible calm wind condition."

Accident investigation:
cover
Investigating agency: CAB
Status: Investigation completed
Duration: 111 days (4 months)
Accident number: File No. 1-0064
Download report: Final report

Classification:
Locked rudders/ailerons/gustlock

Sources:
» CAB Accident Investigation Report


Photos

photo of Douglas DC-4 NC30046
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Map
This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from New York-La Guardia Airport, NY to Cleveland Municipal Airport, OH as the crow flies is 667 km (417 miles).
Accident location: Approximate; accuracy within a few kilometers.

This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Douglas DC-4

  • 1242+ built
  • 63rd loss
  • 28th fatal accident
  • 3rd worst accident (at the time)
  • 26th worst accident (currently)
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 United States of America
  • The worst accident (at the time)
  • 76th worst accident (currently)
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