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Last updated: 5 August 2021
Date:Wednesday 12 September 1951
Type:Boeing 377 Stratocruiser 10-34
Operator:United Airlines
Registration: N31230
MSN: 15970/61
First flight: 1949-12-19 (1 year 9 months)
Total airframe hrs:1971
Engines: 4 Pratt & Whitney R-4360-B6
Crew:Fatalities: 3 / Occupants: 3
Passengers:Fatalities: 0 / Occupants: 0
Total:Fatalities: 3 / Occupants: 3
Aircraft damage: Damaged beyond repair
Location:off Redwood City, CA (   United States of America)
Phase: Approach (APR)
Departure airport:San Francisco International Airport, CA (SFO/KSFO), United States of America
Destination airport:San Francisco International Airport, CA (SFO/KSFO), United States of America
United Air Lines' Boeing Stratocruiser "Mainliner Oahu" was being used for a semi-annual instrument check of a captain. In addition, consideration had been given to investigating the feasibility of using the Oakland, California, Municipal Airport for certain phases of crew training in this type aircraft for a new class of pilots and flight engineers which was to convene that afternoon. The flight departed at 09:42 and reported on top of the broken scattered clouds four minutes later. The flight proceeded to Oakland, where a simulated ILS approach was carried out, followed by a missed approach procedure. The flight again reported on top at 10:36. Another simulated ILS approach was requested of the Oakland tower but the flight was advised that there would be a delay due to other traffic. In view of this, the pilot decided to return to San Francisco. At 10:39, the flight was cleared for an ILS approach to the San Francisco Airport. The aircraft, with No. 4 propeller feathered, stalled and abruptly dived from an altitude of approximately 300 feet and was demolished upon impact in San Francisco Bay.

Probable Cause:

PROBABLE CAUSE: "An inadvertent stall at a low altitude from which recovery was not effected."

Loss of control

» CAB File No. 1-0089


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Boeing 377

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