TWA's introduction of the Constellation in 1946 put American and United at a serious disadvantage on their all important transcontinental routes, but it also disadvantaged Lockheed who were tied to an agreement, with Howard Hughes, which stopped them selling to his competitors. This pushed American towards Douglas and hundreds of sales of the new DC-6 and DC-7 throughout the 1950s.
TWA's lead in operating fast and pressurised Connie equipment against American and United's ex-USAAF C-54s was tempered somewhat by the types temporary grounding in 1946, however it wasn't until May 1947 that American could put the competing DC-6 into service. Douglas undertook a joint delivery ceremony to American and United in March but by then several aircraft had already been delivered. It was United though that was first to put the Six into service, on April 27, 1947. American followed with its first transcontinental service on May 20. The westbound leg took 11 hours and the eastbound 10 hours. Travelling at 300 mph and being pressurised itself the DC-6 was a capable Connie competitor.
The initial service entry of the DC-6 was far from smooth as in November 1947 the type was voluntarily withdrawn from service due to serious safety problems related to inflight fires caused by fuel leakage into the cabin heating system. This had already led to the loss of a United aircraft and the emergency landing of an American DC-6. Fixing the problem took until March 14, 1948, but subsequent to that American was able to replace almost its entire fleet of DC-4 / C-54s. American advertised its DC-6s as 'Five Star Flagships'. They took delivery of 50 standard DC-6s registered N90701 to N90750 between March 1947 and May 1948.
In 1948 American introduced DC-6 "Skysleeper" flights with aircraft refitted with 8 sleeper berths and 36 regular seats. The lower berths could accommodate two passengers, which seems risque for the time!
In 1949 American introduced Air Coach services. Though initially flown with DC-4s the service was really designed for the DC-6s, reconfigured with 70 passengers, rather than the normal 52. The fares were set so the 70 passengers would generate the same level of profit as the original 52. When the DC-6s were used from 1950 the service, operating from New York-Chicago-Los Angeles, was known as the DC-6 Blue Ribbon Aircoach.
Douglas, American and United took the lead over TWA and Lockheed in April 1951 with the introduction of the new DC-6B, a slightly stretched DC-6 that would prove to be the most economic piston prop-liner of all time. It wasn't until late 1952 that TWA could counter with the L-1049A. American started DC-6B services 18 days after United on April 29, 1951. American purchased 35 DC-6A/Bs (the A was the freight version) registered from N90751 to N90785 with deliveries into October 1957 (though the last passenger variant was delivered in May 1953). N90751 was first 'Flagship California' and then 'Flagship Los Angeles' later in her life.