The NTSB found that ground handlers did not properly close the air start access door due to an interruption in their procedures: when a supervisor realized that the headset used for communication with the flight crew was not working, he switched to using hand signals mid-routine. In the confusion the supervisor signaled the flight to taxi before the air start hose had been disconnected. After the supervisor realized his error and signaled the flight crew to make an emergency stop, the hose was successfully disconnected but the air start access door was not closed.