Brief Summary
This video tells the story of two accidents involving Douglas DC-6 aircraft in the late 1940s. The first accident, United Airlines Flight 608, resulted in the deaths of all 52 people on board due to a fire caused by a design flaw in the fuel system. The second accident, an American Airlines DC-6 fire in Gallup, New Mexico, resulted in no fatalities but led to the grounding of all DC-6 aircraft in the United States. The investigation into these accidents revealed a series of design flaws and safety oversights by Douglas, including a fuel transfer system that could cause fuel to overflow and a fire extinguishing system that could incapacitate the crew with carbon dioxide. These accidents led to significant changes in aviation safety regulations and practices, including the mandatory use of full-face fume-proof oxygen masks for pilots.
- The DC-6 had a fuel transfer system that could cause fuel to overflow and ignite the cabin heater.
- The DC-6's fire extinguishing system could release hazardous amounts of carbon dioxide, potentially incapacitating the crew.
The DC-6 Fuel System Flaw
This chapter details the fuel system design flaw that led to the fire on United Airlines Flight 608. The DC-6's fuel system was inherited from the DC-4 and had eight fuel tanks, with a main and alternate tank for each engine. The pilots could manually configure which tank supplied each engine, but the system was complex and required careful monitoring. The outboard alternate tanks were larger than the inboard alternate tanks, which meant that the inboard tanks could run out of fuel before the outboard tanks. The pilots often used a fuel transfer procedure to equalize the fuel levels in the tanks, but this procedure was not intended by Douglas and could cause fuel to overflow from the tank vents.
The DC-6 Fire Extinguishing System Flaw
This chapter focuses on the fire extinguishing system flaw that led to the incapacitation of the crew on United Airlines Flight 624. After the initial DC-6 accidents, Douglas redesigned the fire extinguishing system, increasing the number of extinguishers in the underfloor compartment. This change required new flight tests to demonstrate compliance with safety regulations, but Douglas did not conduct these tests adequately. The fire extinguishers used carbon dioxide, which could displace oxygen and incapacitate the crew if released in high concentrations. Douglas also failed to design the system so that the cabin pressure relief valve could be activated simultaneously with the extinguishers, making the procedure overly complex in an emergency situation.
