I’ve always been amazed at the speed with which the DC 7s and L-1649 propeller airliners were withdrawn from service when jets came in. Did AA, UA, and TWA make any money on them? I realize they were fiercely competitive on coast to coast routes and to Europe (for TWA) but I wonder how quickly they were allowed to depreciate them and if they had to take a write off when they were retired?
My understanding is that the engines were difficult and expensive to maintain, which is why DC 6s and L-1011 planes were used longer. Pushing reciprocating engines to the limits for high performance came at a price.
I know that DL and NW flew them longer than UA and AA. I don’t know how long EA flew their DC 7Bs.
You are absolutely correct that the DC-7s as well as the L-1049C/G/H and L-1649 were retired early because of engine reliability problems. The way I think about it is that there was no easy way to squeeze over 3,000 horsepower out of a radial engine. The two bad options were either turbocharging, which Wright did with the R-3350 for the DC-7s and Super Constellations, or adding more rows of cylinders, which Pratt&Whitney did with the R-4360 for the Stratocruiser. Both options gave the engines bad thermal dynamics. They both ran so hot that they were prone to inflight shutdowns and cracked cylinders. The reason the airlines needed the power, though, is that it was the only way to give an airplane as heavy as a DC-7 or a Super Connie transcontinental/transatlantic range. The R-2800 on the DC-6 was far more reliable, but at only 2,500hp, you were just too payload and range limited. So for five years starting in 1953, the solution was to turbocharge the Wright R-3350 and limp along until the jets came in in 1958. Once that happened, the jets took over all the long range flying, and you could relegate the remaining piston fleet to short haul. You no longer needed the extra horsepower on short haul, so you could retire the less reliable planes. Thus, United ended piston operations with the DC-6, and TWA with the non-turbo L-749A. Northwest did run the DC-7C until 1967, but that was because they could use the extra horsepower to lift more freight on their transpacific freight ops for a short window before they had enough 707 lift to retire the pistons altogether.