ASN Wikibase Occurrence # 336865
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| Date: | Friday 24 October 1947 |
| Time: | 12:29 |
| Type: |  Douglas DC-6 |
| Owner/operator: | United Airlines |
| Registration: | NC37510 |
| MSN: | 42875/17 |
| Year of manufacture: | 1947 |
| Total airframe hrs: | 933 hours |
| Engine model: | Pratt & Whitney R-2800 |
| Fatalities: | Fatalities: 52 / Occupants: 52 |
| Aircraft damage: | Destroyed, written off |
| Category: | Accident |
| Location: | 2,4 km SE of Bryce Canyon Airport, UT (BCE) -
 United States of America
|
| Phase: | En route |
| Nature: | Passenger - Scheduled |
| Departure airport: | Los Angeles Airport, CA (LAX/KLAX) |
| Chicago Municipal Airport, IL (MDW/KMDW) | |
| Investigating agency: | CAB |
| Confidence Rating: |  Accident investigation report completed and information captured |
United Airlines flight 608 departed Los Angeles at 10:23 for a non-stop flight to Chicago. The airplane climbed to 19,000 feet and proceeded VFR over Fontana, Daggett, Silver Lake, Las Vegas, and Saint George. At 12:21 Flight 608 reported that a fire had been detected in the baggage compartment which the crew was unable to extinguish. The report added that the cabin was filled with smoke and that the flight was attempting to make an emergency landing at Bryce Canyon Airport in Utah. The fire had erupted in the center section in the vicinity of the right wing fillet. Small parts of the airplane were lost in flight and at least one of the emergency landing flares which are located at the trailing edge of the right wing fillet ignited in flight.
Shortly thereafter the flight again reported that the "tail is going out-we may get down and we may not." At 12:26 another transmission was received from the flight indicating that it was going into the "best place available." One minute later the flight reported "we may make it-approaching a strip." This was the last contact with the flight. It crashed at 12:29 before it was able to reach the airport.
After the accident, investigators noted that the DC-6 airplane design included a No.3 alternate fuel tank vent outlet that was located on the right side of the fuselage near the leading edge of the wing and close to the bottom wing fillet. Approximately 10 feet aft of this point and slightly to the left there was an air scoop which served as a source of cabin heater combustion air and cooling air for the cabin supercharger air after-cooler and cabin supercharger oil cooler. Flight tests conducted with other model DC-6 aircraft subsequent to the accident revealed that overflow from the No. 3 alternate tank through the air vent line and out the vent outlet would sweep back in the slip stream toward the cabin heater combustion air intake scoop and that a considerable quantity of fuel would enter the scoop. Ground tests clearly demonstrated that, under conditions simulating the entry of fuel overflow into the scoop inflight while the heater was operating, the cabin heater could be expected to backfire and thereby propagate flame downstream into the air scoop. Incoming fuel would, thereafter, be expected to continue to burn in the air scoop and duct.
PROBABLE CAUSE: "The combustion of gasoline which had entered the cabin heater air intake scoop from the No.3 alternate tank vent due to inadvertent overflow during the transfer of fuel from the No.4 alternate tank. The failure of the manufacturer and the Civil Aeronautics Administration to exercise full caution in the analysis of the fuel system of the DC-6 relative to proper location of fuel tank vents to provide non-hazardous location for fuel drainage, as required by existing regulations, and the insufficient attentiveness on the part of the manufacturer, the Civil Aeronautics Administration, and the air carriers to the procedures of fuel management employed by pilots operating DC-6 aircraft, were contributing factors."
Accident investigation:
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