In answer to Bob's question ("Can we name the fallen flag Airlines?"), here's the larger airlines I can think of off the top of my head that were alive in the 50s & 60s that are no longer with us. These are airlines that held a Certificate of Public Convenience by the Civil Aeronautics Board. (Only USA airilnes listed).
Braniff (orignal) - went bankrupt
Capital - merged into United
Texas International - eventually merged into Continental
Eastern - eventually merged into Continental
National (the original one) - Merged into Pan Am
Pan Am - bankrupted, out of business
TWA - merged into American
Western - merged into Delta
Northeast - merged into Delta
PSA - merged into USAir (before or after name changed from Allegheny?)
Lake Central - merged into Allegheny (now called US Airways)
Air Cal - merged into American
Seaboard World - merged into Flying Tigers
Flying Tigers - merged in FedEx
Mackey - merged into Eastern
Pacific Northern - merged into Western
Reeve Aleutian - out of business
Alaska Coastal - not sure if merged or out of business
Ellis - not sure if merged or out of business (don't believe this is the full name of the airline)
Wien - out of business
West Coast/Pacific/Bonanza - 3 way merger to former Air West (the only 3 at once merger that I know of)
Hughes AirWest - merged into Republic (this is the same airline as Air West above)
Southern - merged into North Central to form Republic
Republic - Merged into Northwest
Ozark - merged into TWA
Panagra - merged into Braniff
Mid Continent - merged into Braniff?
Frontier - merged into PeopleExpress (PeopleExpress is no longer with us but
David
Technically speaking, the USA doesn't have "flag carriers," which I take to mean airlines owned solely or largely by a nation's government to display the flag abroad. Pan Am, however, did come close to being a flag carrier