The turbojet engine JT3C-6 and JT3C-7 entered commercial service on American Airlines Boeing 707/720 Aircraft after a considerable period of experience resulting from military J57 operation. Although the commercial operation uncovered problem areas, the causes were defined and the engine reliability and serviceability responded to various improvement programs. The time between overhauls (TBO) increased from 800 to 2100 hr at a rate unparalled in commercial engine operation. The turbofan is now going through a period of commercial “growing pains.” Problems have resulted from higher thrust, use of new materials, higher temperatures within and outside the engine, complexities of a fan air-thrust reverser, and so on. The airframe and engine manufacturers have defined these problems and together with the commercial operators are engaged in programs to insure performance and reliability compatible with the tremendous success of the first generation JT3C-6 and JT3C-7 turbojets.

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