What happened
On 27 March 2022, a flight instructor and a student pilot departed Lanseria International Aerodrome for a training flight intended to practice stall exercises. The flight, conducted under visual flight rules, was being performed by a Part 141 training organization. While cruising at approximately 5,500 feet above mean sea level, the instructor requested a climb to 6,000 feet by increasing power. However, the engine failed to respond to the throttle increase.
The instructor took control of the Cessna 172H Skyhawk and attempted to troubleshoot the engine failure using the onboard checklist, including adjusting the fuel mixture and magnetos. Despite these efforts, the engine revolutions continued to fluctuate, and the aircraft began losing altitude. The instructor identified an open field near Hartbeespoort for an emergency landing and glided the aircraft toward the site.
During the landing roll, the aircraft encountered rugged terrain. The nose wheel struck a 40-centimeter-high anthill, causing the nose-gear strut to fail. This impact caused the aircraft to nose over, eventually coming to rest in an inverted position. Both occupants sustained minor injuries, but the aircraft suffered substantial damage.
The investigation
SACAA AIID examined the aircraft's maintenance history and found that the Cessna 172H was airworthy and had been maintained according to regulations, with the most recent periodic inspection completed shortly before the flight. The engine, a Lycoming O-320-E2A, had been bench-tested and was found to be functioning correctly.
The investigation focused on the atmospheric conditions and engine operation. At the time of the accident, the temperature was 24°C with a dew point of 13°C. According to carburetor icing charts, these conditions were conducive to moderate icing at cruise power. The investigation also reviewed the flight school's emergency checklists and the pilots' pre-flight preparations.
Findings
- Carburetor ice formation occurred during the climb, which caused the reduction in engine power and the subsequent loss of altitude.
- The pilots did not check the temperature and dew point prior to departure, leaving them unaware that the weather conditions favored ice accumulation.
- The training organization's pilot checklist did not include instructions for using the carburetor heat control to mitigate engine roughness or recover from icing.
Safety action
- The AIID recommends that the flight school update its pilot checklists to include specific procedures for recovering from or preventing carburetor icing.
- It is recommended that the training organization require pilots to reference the aircraft's Pilot's Operating Handbook (POH) in addition to the school's summary checklist.
- The AIID recommends that the flight school mandate the checking of weather information, specifically temperature and dew point, before every flight to identify icing risks.