 The NTSB report noted that between 1970 and 1973, seven separate cases involving a single leading edge slat extension and separation were reported, but none of these reports indicated whether or not the slat extension was due to flight crew involvement.Records after 1974 did include this information, and (other than Flight 174) only two slat extension problems were reported between 1974 and the close of the NTSB's investigation in 1981, one of which was inadvertently caused by the flight crew.The flight crew testified that they had not engaged the flaps, and the NTSB concluded that "if the flightcrew's recollections are accurate," the slat extension must have been caused by a mechanical failure or defect.