Aircraft and Test Background
The aircraft, registration 74-1683, was delivered on 17 October to TAB1 at Wagner Field, a disused auxiliary airfield at Eglin Air Force Base, Florida. Between 19 October and 28 October, numerous flights were conducted to test various aspects of the aircraft, including its double-slotted flaps system. This system enabled the C-130 to fly at 85 knots on final approach with a very steep eight-degree glide slope. All aspects functioned flawlessly, and a full profile test was scheduled for 29 October.
The Test Flight
The test's takeoff phase was executed flawlessly, setting several short takeoff records. After takeoff, the Lockheed test crew assessed that the computer used to command the firing of the rockets during the landing sequence needed further calibration. They elected to manually input commands for the rocket firings.
The aircraft was equipped with reverse-mounted (forward-facing) eight ASROC rockets for decelerating forward speed. These rockets were situated in pairs on the fuselage's upper curvature behind the cockpit and at the midpoint of each side of the fuselage beneath the uppers. Testing had determined that the upper pairs, fired sequentially, could be ignited while still airborne—specifically, at 20 feet above ground—but the lower pairs could only be fired after the aircraft was on the ground. Descent-braking rockets were also part of the firing sequence.
The Accident
During the landing sequence, the flight engineer, blinded by the firing of the upper deceleration rockets, mistakenly thought the aircraft was on the runway and fired the lower set early. The descent-braking rockets did not fire at all. Unofficial disclaimers later alleged by some Lockheed test crew members asserted that the lower rockets fired themselves through an undetermined computer or electrical malfunction, which simultaneously failed to fire the descent-braking rockets.
As a result, the aircraft's forward flight was immediately reduced to nearly zero, causing it to drop hard onto the runway. The impact broke the starboard wing between the third and fourth engines. During rollout, the trailing wing ignited a fire. A medical evacuation helicopter dispersed the flame, and crash response teams extinguished the fire within eight seconds of the aircraft stopping, enabling the crew to exit safely.
Aftermath
The aircraft, 74-1683, was dismantled and buried on-site for security reasons. Most of its unique systems were salvaged.