Serious Incident Involving a Maule M7-235C at Tábor Airport (OK-JAA)

Overview and Event Description On 3 June 2018, at 10:46 UTC, a Maule M7-235C aircraft, registration OK-JAA, operated by Letecké akrobatické centrum ČR, z. s., was conducting glider tow operations at Tábor Airport (LKTA). During the tow, the pilot detected the smell of burnt laminate in the cabin, followed by smoke. The glider pilot observed a faint smoke trail behind the tow aircraft. After communicating with the tow pilot, the glider pilot released the tow at 350 m AGL and continued flight. The tow pilot declared an emergency on TÁBOR RADIO 122.610 MHz, requested to land on runway 34, and shut down the engine during descent for safety. The aircraft landed on runway 34 and taxied off to the left to clear the runway. No injuries were reported. ## Aircraft and Pilot Information The aircraft was a single-engine, four- to five-seat high-wing monoplane with a conventional tail and fixed tailwheel landing gear, which could be replaced with floats. Its maximum takeoff weight was 1,135 kg. The aircraft was powered by a Lycoming O-540-B4B5 six-cylinder piston engine producing 175 kW, driving a Hartzell HC-CJY-1RF/F7693F propeller. The aircraft had a total time of 1,683 hours and was manufactured in 2004. A 50-hour inspection performed on 4 May 2018 at EEA Tech spol. s.r.o. in Moravská Třebová found no damage or defects to the exhaust or heat exchanger. The pilot was a 24-year-old male holding a valid Czech PPL(A) with SEP Land, NIGHT, AEROBATICS, and TOWING-S qualifications, a valid Class 1 medical certificate without limitations, and a valid restricted radiotelephony license. His total flight time was 287 hours, with 105 hours on type and 98 hours as pilot-in-command on type. ## Damage and Technical Findings After the emergency landing, the aircraft showed the following damage: a burned hole in the engine cowling, burns to both the inner and outer exhaust shroud at the location of the heat exchanger, and destruction of the cabin heating heat exchanger. The investigation determined that the exhaust body cracked due to high temperatures combined with operational engine vibrations. The heat exchanger also cracked, allowing hot exhaust gases to escape into the inner side of the engine cowling. The gases ignited the carbon cowling, but the flame was extinguished in flight by airflow. The pilot shut off the fuel supply and followed the flight manual procedures. After engine shutdown, the fire and smoke ceased. The exhaust and heat exchanger were correctly installed. Part of the exhaust muffler shroud and the heat exchanger body disintegrated. The muffler damage was most likely caused by operational wear and vibrations from thermal loading of the exhaust material. Inspection of the fire wall and other engine compartment components found no additional defects or damage. ## Conclusions The investigation found that the aircraft had valid technical and operational documentation and was airworthy, the pilot had valid documentation and was qualified, and the pilot handled the event correctly in accordance with the type operating manual. The cause of the serious incident was damage to the engine exhaust body by high temperatures in combination with operational engine vibrations. The investigation was conducted in accordance with Regulation (EU) No 996/2010, Czech Act No. 49/1997, and Annex 13 to the Chicago Convention, with the sole purpose of preventing future accidents and incidents without determining blame or liability. No safety recommendations were issued.