One of my jobs was for a subsidiary of a European plane maker. Some of their critical systems were written in Fortran 77 and was decades old in some cases. I ha

One of my jobs was for a subsidiary of a European plane maker. Some of their critical systems were written in Fortran 77 and was decades old in some cases. I have no clue about F77 or aircraft engineering, but my team was told repeatedly that these software ran flawlessly and nobody was ever to touch it (we made some fancy JAVA UI and called F77 executables in the background). I guess a time will come to sunset, but just not yet. As above, may be these COBOL systems have been battle tested for a long time and they are good. Other reasons could be, "if it ain't broke then why fix it?" or that there aren't enough people to act as a bridge between the old and new systems so it is hard to do such projects (as other comments have pointed out)