June 27, 1972 Daniel Applegate, Director of Product Engineering for Convair, the fuselage contractor, wrote a memo to his supervisors detailing potential problems of cargo door. The problem was first recognized in Aug 69. The same thing had also happened in a ground test in 1970.
Recognized design flaws - floor, latch
FAA director John Shaffer and McDonnel Douglas President Jackson McGowan reached a gentleman's agreement to voluntarily fix problem, but no further official action was taken.
In July 1972, Three inspectors at Long Beach plant certified that Ship 29 had been modified (but it was not). Two years later, after leaving Paris, its cargo door blew off at 13,000 feet, killing 346 people.
McDonnel Douglas was in precarious financial condition - trying to beat Lockheed L1011 to market
Convair did not push too hard, since by contract, they may have been held liable for the costs of all design changes
Engineers pressed the matter through normal channels to the highest levels within both companies, but did not take it any further action, Standard operating procedure at McDonnell Douglas and Convair was for engineers to defer to upper management, even though they were aware of serious design flaws