What happened
Following a flight from Kelly AFB, a McDonnell Douglas DC-9 arrived at Carswell AFB at 01:12 CST. After USAF personnel completed cargo transfer operations, the engines were started at 02:04. The aircraft departed from runway 17 at 02:09.
During or immediately after rotation, the main cargo door became unlatched. The crew declared an emergency and climbed to 2500 feet MSL. While performing a right turn approximately 5nm north of the airfield, the captain tightened the turn to establish position for the base leg. During this maneuver, aerodynamic loads likely caused the door to swing into a fully open position. This sudden movement created unexpected rolling and yawing moments. The aircraft entered a critical bank angle and lost altitude, ultimately striking the ground in an inverted, nose-down, left-wing-low attitude, resulting in the disintegration of the airframe.
Findings
Investigations revealed that when the first officer was securing the cargo door, the 'T' handle control valve was not held in the closed position long enough for the latching hooks to properly seat over the sill spools. Furthermore, external indicators for the latched and locked status were applied incorrectly, leading the crew to believe the door was secure when it was not.
The malfunction of an open door warning light switch also played a role, as wiring issues rendered the entire warning system ineffective. The investigation concluded that the loss of control followed the in-flight opening of the improperly secured cargo door.