History of the Flight
On 10 November 2019, a TECNAM P92-JS registered as F-HBSV was operating an instructional cross-country flight from Bellegarde-Vouvray aerodrome to Chambéry Challes-les-Eaux aerodrome. The flight was crewed by a student-pilot and an instructor. After overflying the destination aerodrome at 3,000 ft, the student joined the downwind leg at 2,000 ft for a left-hand circuit to paved runway 32. Carburettor heat was applied during the descent. On short final, approximately 50 ft above the ground and before the runway midpoint, the instructor instructed a go-around due to the aircraft being too high on the approach. About ten seconds after initiating the go-around, at around 250 ft above ground, the instructor noticed severe vibrations and a reduction in power. She took control, briefly activating carburettor heat with no effect, then returned the control to its previous position and adjusted power to stop the vibrations. Unable to maintain level flight and with no suitable area for an emergency landing ahead, she elected to turn left and land at the aerodrome. The aircraft touched down on runway 14 approximately 100 m from its end, overran the runway, and traversed grass. Crossing a rut caused the nose gear to fail, and the aircraft came to a stop. The aircraft sustained damage.
Additional Information
Meteorological Information
Météo-France estimated the following conditions at Chambéry Challes-les-Eaux: north to north-westerly wind of 5 to 8 kt; visibility greater than 10 km; overcast sky with cloud layer between 2,000 and 3,000 ft; temperature 8 °C, dew point 5 °C; QNH 1011 hPa.
Crew Information
The instructor held a CPL(A) and FI(A) rating, with 440 total flight hours, including 101 hours as an instructor and 70 hours on F-HBSV. The student-pilot had logged 67 flight hours, 62 of which were dual.
Aircraft Information
The TECNAM P92-JS was built in 2010 and had accumulated 3,446 flight hours. The Rotax 912-S2-01 engine was installed in February 2016 and had 1,488.36 operating hours. Two carburettors (type 64/32) were installed new in May 2019, with no prior incidents. The next scheduled maintenance was at 3,462 airframe hours.
Examination of the Aircraft
The hot air supply duct, which provides heated air to the carburettors when carburettor heat is selected, was found broken. The duct comprised a rubber casing and a metal spiral that had corroded and torn the casing. It could not be determined when the break occurred. If present before the flight, the duct's failure would have limited or negated carburettor heat effectiveness during the descent prior to the go-around. No other anomalies were found in the airframe, engine, or carburettors.
Statements
The instructor stated that after adjusting power to eliminate vibrations, available power was insufficient to maintain level flight. Carburettor heat was used during each descent phase of the flight. No engine anomalies were detected during pre-takeoff tests at Bellegarde-Vouvray.
Similar Cases
Several similar occurrences involving sudden power reductions, often with vibrations, were identified on various aircraft equipped with Rotax 912 engines. These events frequently occurred in initial climb. Technical examinations could not explain them. Some carburettors showed friction marks on throttle valves; on F-HBSV, one carburettor replaced about 200 hours before the accident exhibited such damage. The engine manufacturer attributed this to abnormal vibrations. The BEA considered intake system icing as a possible cause but noted that simple icing diagrams may be insufficient.
Conclusions
The origin of the power reduction could not be determined with certainty. However, it is likely that the hot air supply duct was damaged before the flight, reducing carburettor heat effectiveness. Under the meteorological conditions, this may have favored carburettor icing, leading to the power loss.