What happened
On 14 October 2021, a Beechcraft King Air B9/0, registration ZS-OHB, departed Mossel Bay Aerodrome (FAMO) for a scheduled paratrooping exercise. The flight, conducted under visual meteorological conditions, involved a pilot and 15 parajumpers. After climbing to 16,500 feet, the pilot reduced speed to facilitate the jump.
As the first six jumpers exited the aircraft via a rail fixed above the main door, the aircraft's flight characteristics changed abruptly. Following the exit of the sixth jumper, the left wing pitched upward and then dropped, leading the aircraft into a stall. During the subsequent stall, two additional jumpers exited the aircraft. The aircraft then entered a left-side spin, completing two full rotations before the pilot successfully recovered the aircraft. The remaining seven jumpers stayed on board, and the aircraft returned to Mossel Bay Aerodrome safely at approximately 1630Z.
The investigation
The investigation examined the environmental conditions and the aircraft's configuration during the deployment. Meteorological data indicated visibility of 9,999 meters with light, variable winds and broken clouds at 1,800 feet. The weather was determined not to be a contributing factor. Investigators also reviewed the aircraft's mass, noting that the total weight of the aircraft and 15 jumpers was approximately 8 pounds below the 9,650lb all-up mass.
Findings
The primary cause of the incident was a shift in the center of gravity (CoG) toward the rear of the aircraft. This change in in-flight configuration, triggered by the movement of jumpers exiting the aircraft, caused the aircraft to stall and enter a left-side spin.