 They also determined that it was "impossible" for the flaps to extend without manipulating the controls.After eliminating all individual and combined sources of mechanical failure, the NTSB ruled that the extension of the slats was due to the flight crew manipulating the flap/slat controls in an inappropriate manner.Investigators believed that 727 pilots (in general, and this flight specifically) were setting the trailing edge flaps to two degrees during high altitude cruise, while at the same time pulling the circuit breaker for the slats so that they would not activate.