Investigation Summary
The investigation centered on the configuration of the Boeing 377's cowl flaps, which are panels used to regulate engine temperature. On the Stratocruiser, open cowl flaps significantly disrupt airflow over the wing's upper surface. When the crew retracted the wing flaps at 145 knots, the resulting loss of lift and increased turbulence caused the aircraft, named 'Stratocruiser Tokyo', to buffet violently and roll left. The captain, Robert Reeve Heard, suspected a 'split-flap' condition, where flaps on one wing retract while the others remain extended. This diagnosis led him to avoid turning the aircraft, as asymmetric lift makes maneuvering extremely hazardous. Civil Aeronautics Board (CAB) investigators discovered that the flight engineer, Vernon Thomsen, had recently requalified on the B-377 but had spent the majority of his recent flying time on the Lockheed L-1049 Super Constellation and Douglas DC-6. Crucially, the cowl flap controls on the L-1049 moved in the opposite direction to those on the B-377. Thomsen likely moved the switches to what he believed was the 'closed' position, but actually left them fully open. The wreckage, recovered from 430 feet of water, confirmed all cowl flaps were in the full-open position.
Final Conclusions
The Civil Aeronautics Board determined the probable cause was the flight engineer's failure to close the engine cowl flaps prior to takeoff, followed by the captain's incorrect analysis of the resulting control difficulties. The Board noted that the captain's misidentification occurred under conditions of great urgency with extremely limited time for decision-making. The flight engineer's lack of recent experience on the B-377 type and the conflicting control designs between the B-377 and other aircraft in the fleet were cited as significant factors.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Robert Reeve Heard
First Officer
Gene Paul Johnson
Systems & Failure Modes
Cowl Flaps
Engine cooling panels that, when left open on the B-377, create significant aerodynamic interference with the wing, leading to buffeting and reduced lift.
Wing Flaps
High-lift devices; their retraction at low altitude while cowl flaps were open triggered the stall and buffeting.
Interesting Facts
- 01The water temperature in Puget Sound at the time of the accident was 42°F (6°C).
- 02All 38 people on board successfully exited the aircraft before it sank.
- 03The five fatalities were caused by hypothermia, not the impact of the ditching.
- 04The aircraft was recovered from the seabed for investigation, revealing the cowl flaps were fully open.
- 05The flight engineer had less than two hours of flight time on the B-377 in the 90 days preceding the accident.
Safety Actions & Advisories
Control Standardization
Source ↗The investigation highlighted the danger of conflicting control designs between different aircraft types in a single fleet, specifically the opposite operation of cowl flap switches on the B-377 versus the L-1049, leading to industry-wide discussions on cockpit standardization for multi-type qualified crews.