1947 — Oct 24, United Air 608 fire and emer. lndg. attempt crash ~Bryce Canyon AP, UT–52
Compiled by Wayne Blanchard 10-6-2023 for upload to: https://www.usdeadlyevents.com/
–52 AP. “52 Plunge to Fiery Death In Utah Crash…” Bridgeport Telegram (CN), Oct 25, 1947.
–52 Aviation Safety Network. Accident Description. United Air Lines Flight 608.
–52 Civil Aeronautics Board. United Air Lines, Inc., Bryce Canyon, Utah, October 24, 1947.
–52 Eckert. “Fatal commercial air transport crashes, 1924-1981.” AJFM&P, 3/1, Mar 1982, p53.
–52 Haine, Edgar A. Disaster in the Air. New York: Cornwall Books, 2000, p. 247.
Narrative Information
Civil Aeronautics Board Accident Investigation Report (SA-153/File No. 1-0097-47):
“The Accident
“United Air Lines’ Flight 608 crashed at 1229 MST, October 24, 1947 1½ miles southeast of Bryce Canyon Airport, Utah, during an attempted emergency landing resulting from a fire in flight. The aircraft, a Model DC-6, NC 37510, was demolished by impact and fire, and all of the 46 passengers and the crew of 6 were killed.
“History of the Flight
“Flight 608 departed Los Angeles California at 10:23 with its destination Chicago, Illinois, to cruise at 19,000 feet according to visual flight rules.[1] Routine position reports were made over Fontana, Daggett and Silver Lake, California; Las Vegas, Nevada; and Saint George, Utah. During the latter report, the flight indicated that it estimated passing over Bryce Canyon, Utah, at 1222.
“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 (BCE). 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.” (ASN, United 608).
“Witnesses who observed the aircraft as it was approaching Bryce Canyon from approximately 20 miles southwest first observed what appeared to be white smoke streaming from the aircraft, followed later by dense black smoke. The first witnesses who observed fire in the bottom of the aircraft at approximately the center-section were located approximately 15 miles south of Bryce Canyon. Until shortly before the moment of impact, the aircraft appeared to be under normal control; however, no witnesses were located who observed the crash
“Investigation
….
“….It was apparent that the aircraft structure began to disintegrate in the center section in the vicinity of the right wing fillet and that parts of the interior of the aircraft in the proximity of this area began to fall from the aircraft early in the development of the fire. The extensiveness of this disintegration is indicated by the fact that the trailing edge of the right wing flap, the main cabin entrance door and the buffet cold box had fallen from the aircraft prior to impact. The extent of burning on parts of the cabin interior, prior to impact, indicates conclusively that the fire in flight was of such severity as to have been unsurvivable for cabin occupants.
“Reconstruction of the fuselage and analysis of the burning of its structural components indicate that the burning in flight took place in an area covering the lower right side of the fuselage beginning at a point in the center section approximately midwing and extending rearward approximately 23 feet and upward along the right side of the fuselage to the top of the window line. Inspection of the structure and components of the cockpit and the rear lounge and toilets show no evidence of burning in flight….
“Discussion
“Investigation of this accident leaves little doubt that the initial fire and the most extensive burning which followed were caused by the combustion of aviation fuel. Reconstruction of the flame path indicates the origin of this fuel to be forward of and approximately in line with the cabin heater combustion air intake scoop. Since the only source of gasoline in this area is the no. 3 alternate tank vent outlet, it is concluded that gasoline overflow through this outlet entered the scoop while in flight, was ignited in the heater and thereafter burned in the scoop and duct.
“In view of the above, the testimony of the captain’s regular co-pilot concerning the flight procedures routinely followed by the captain indicates very strongly that, in the course of transferring fuel from the outboard alternate tanks to the inboard alternate tanks in flight, he failed to stop the transfer in time to prevent the No. 3 alternate tank from overflowing through the vent outlet. The time of discovery of fire aboard the aircraft corresponds very closely to the time at which the crew would be expected to transfer fuel from the outboard alternate tanks to the inboard alternate tanks.
“Early in the course of the investigation it became apparent that the emergency landing flares contributed to the severity of the fire in flight. Although it was apparent that a fire of considerable intensity would have been necessary to ignite these flares, the hazard that their location in the Model DC-6 presented was, nevertheless, recognized. As a result of this investigation, the Board promulgated a special regulation enabling air carriers operating this model aircraft to remove all landing flares until proper location in the aircraft is made….
“Soon after the investigation was initiated, a Modification Board was organized, consisting of representatives of the Civil Aeronautics Board, Douglas Aircraft Company, United Air Lines, Inc., and American Airlines, Inc., the purpose of which was to analyze and improve where possible the component parts and systems of the DC-6. Since the industry voluntarily withdrew the DC-6 from scheduled service on 11 November 1947, a portion of these modifications is now underway. The modification plan required the relocation of the Nos. 2 and 3 alternate tank vent outlets to areas in which no hazardous fuel overflow conditions will exist. In addition, extensive modifications to the electrical system was required to increase the protection against possible fire hazards from this source. Other modifications encompassing the power plant and fire extinguishers were also affected. After the DC-6 was returned to service, operations were limited to certain categories until all modifications had been instituted. For example, operation with the heater was not permitted until extensive modifications had been completed on the cabin supercharging and ventilating systems, cabin heating system, and fire detection and suppression system.
“The investigation clearly established that the origin of the fire in this accident was not in either of the baggage compartments. The Board has been cognizant of the public concern over the possibility of a fire being started in flight as a result of discharge of photo flash bulbs carried in passenger baggage. An extensive study showed that the amount and rate of heat dissipated by the discharge of such bulbs was insufficient to ignite even the most highly flammable materials carried in baggage or express….
“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 Board determines that the probable cause of this accident was 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. Contributing factors were the improper location of the No. 3 alternate tank air vent outlet and the lack of instructions provided DC-6 flight crews concerning hazards associated with fuel transfer.
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.”
Aviation Safety Network, Flight Safety Foundation, Database, 1947 (United 608. 10-24-1947):
“Follow-up / safety actions
“Airlines voluntarily withdrew the DC-6 from scheduled services on November 11, 1947, in preparation for modifications. Meanwhile, a Modification Board created a list of modifications to the DC-6 design that were to prevent such an accident from happening again.
This modification plan required a.o. the relocation of the Nos. 2 and 3 alternate tank vent outlets to areas in which no hazardous fuel overflow conditions would exist. Guards are required for all fuel booster pump switches. In addition, extensive modification to the electrical system is required to increase the protection against possible fire hazards from this source.
ASN notes that Flight 608 was the first loss of a Douglas DC-6 and the 2nd worst aviation disaster in the U.S. at the time. (Aviation Safety Network. Accident Description, United Air Lines Flight 608)
Associated Press
Oct 25, AP: Flight 608 went down after ‘Trailing smoke and flames for at least 22 miles….just 1,500 yards from the safety of an emergency landing strip.” (AP, Oct 25, 1947, in Bridgeport Telegram, CT.)
Sources
Associated Press. “52 Plunge to Fiery Death In Utah Crash of Airliner.” Bridgeport Telegram (CN), 10-25-1947. At: http://www.newspaperarchive.com/freepdfviewer.aspx?img=4973569
Aviation Safety Network. Accident Description. United Air Lines Flight 608. Accessed 12-20-2008 and 10-6-23 at: http://aviation-safety.net/database/record.php?id=19471024-0
Civil Aeronautics Board. United Air Lines, Inc., Bryce Canyon, Utah, October 24, 1947. Accessed 10-5-2023 at: https://reports.aviation-safety.net/1947/19471024-0_DC6_NC37510.pdf
Eckert, William G. “Fatal commercial air transport crashes, 1924-1981.” American Journal of Forensic Medicine and Pathology, Vol. 3, No. 1, March 1982, Table 1.
Haine, Edgar A. Disaster in the Air. New York: Cornwall Books, 2000, 394 pages.
[1] Haine notes that the flight was then to go on to New York. (p. 242.)