Douglas DC-6

The Douglas DC-6 is a piston-powered airliner and cargo aircraft built by the Douglas Aircraft Company from 1946 to 1958. Originally intended as a military transport near the end of World War II, it was reworked after the war to compete with the Lockheed Constellation in the long-range commercial transport market. More than 700 were built and many still fly in cargo, military, and wildfire control roles.

The DC-6 was known as the C-118 Liftmaster in the United States Air Force service and as the R6D in the United States Navy service prior to 1962, after which all U.S. Navy variants were also designated as the C-118.

The United States Army Air Forces commissioned the DC-6 project as the XC-112 in 1944. The Army Air Forces wanted a lengthened, pressurized version of the DC-4-based C-54 Skymaster transport with more powerful engines. By the time the prototype XC-112A flew on 15 February 1946, the war was over, the USAAF had rescinded its requirement, and the aircraft was converted to YC-112A, being sold in 1955.

Douglas Aircraft modified the design into a civil transport 80 in (200 cm) longer than the DC-4. The civil DC-6 first flew on 29 June 1946, being retained by Douglas for testing. The first airline deliveries were to American Airlines and United Airlines on 24 November 1946. A series of inflight fires (including the fatal crash of United Airlines Flight 608) grounded the DC-6 fleet in 1947. The cause was found to be a fuel vent next to the cabin cooling turbine intake; all DC-6s were modified, and the fleet was flying again after four months on the ground.