What happened
On 19 March 2011, a Cessna 150M, registration ZS-JKN, was conducting a private VFR flight from Nelspruit Aerodrome to Lanseria International Airport. While cruising at 500ft AGL with a true airspeed of 95kt, the pilot encountered a sudden downdraft that caused a loss of lift and an increased rate of sink.
In an attempt to recover, the pilot pulled back on the controls, eventually arresting the sink rate at approximately 100ft AGL. Facing rising terrain ahead, the pilot deployed 10 degrees of flaps to initiate a climb. However, the aircraft was unable to gain sufficient altitude to clear the obstacles, forcing the pilot to execute an emergency landing in a nearby grassy field.
Upon touchdown, the aircraft's undercarriage entered soft mud, causing the plane to overturn onto its back. The impact resulted in the bending of the nose landing gear and the separation of the right main landing gear. The aircraft also sustained damage to the right wing and the tail section. The pilot sustained minor injuries to the head and face and was transported to a local hospital.
The investigation
SACAA AIID examined the flight circumstances and the mechanical state of the aircraft. The investigation confirmed that the pilot held a valid commercial license and medical certificate, and possessed sufficient experience with the aircraft type. The Cessna 150M was found to have a valid Certificate of Airworthiness and had been maintained by an authorized maintenance organization.
Findings
- The pilot was flying at an altitude of only 500ft AGL, which was insufficient for the terrain.
- The encounter with rising terrain, combined with the loss of altitude from the downdraft, created an unsafe flight condition.
- The pilot failed to maintain a safe altitude for the route, leaving no margin for error when the atmospheric disturbance occurred.