What happened
On 30 August 2008, an Ayres S2R-T34, registration ZS-OZM, crashed into a tree plantation in the Havemanshoogte area near Melmoth, KwaZulu-Natal. The aircraft was engaged in aerial fire suppression duties during a period of intense wildfires in the province. Shortly after departing Kataza Aerodrome for its fourth water load of the day, the aircraft entered a steep, vertical nose-down descent and impacted the ground approximately 1,356 meters from the runway.
The pilot, a 68-year-old commercial pilot with extensive experience, was the sole occupant of the aircraft. The impact destroyed the aircraft, and the pilot sustained fatal injuries. At the time of the accident, the area was experiencing significant wind conditions, with gusts recorded between 15 and 35 knots.
The investigation
SACAA AIID investigators examined the wreckage and the circumstances surrounding the flight. The investigation confirmed that the aircraft was well-maintained, with a valid Certificate of Airworthiness and no evidence of mechanical or airframe failure prior to the crash. Evidence at the impact site, including a tree stump severed by the propeller, indicated that the engine was still producing power at the moment of impact.
A critical component of the investigation involved a post-mortem toxicological analysis. While the pilot had no alcohol or narcotics in his system, the tests revealed a carbon monoxide (CO) hemoglobin saturation of 2/21.3%. Investigators also noted that the aircraft was operating in an environment with heavy smoke from active wildfires, which serves as a potential source of CO.
Findings
- The primary cause of the accident was the pilot loss of control due to the effects of hypoxia.
- Toxicological results confirmed significant exposure to carbon monoxide, which reached a level capable of causing drowsiness and impaired complex task execution.
- The presence of carbon monoxide in the pilot's bloodstream likely led to hypemic hypoxia, reducing the blood's ability to transport oxygen to vital organs.
- High wind speeds and turbulence were present during the operation, though the aircraft was within weight limits for takeoff.
Safety action
Following the investigation, the following safety considerations were noted:
- The importance of alerting the aviation community to the hazards of carbon monoxide and the benefits of installing CO detectors in aircraft.
- The need for a feasibility study regarding the use of supplemental oxygen for flight crews performing aerial firefighting operations in heavy smoke environments.