What happened
On June 3, 2018, a Maule-M7-235 C, registration OK-JAA, was performing glider towing operations at Tábor Airport (LKTA). During the towing sequence, the pilot detected the smell of burning composite material inside the cockpit, followed by the appearance of smoke. The glider pilot observed a faint smoke trail trailing behind the towing aircraft.
After communicating with the glider pilot, who disconnected from the tow at an altitude of 350 m AGL, the pilot of the Maule-ARG-235 C declared an emergency landing on runway 34. To ensure safety, the pilot shut down the engine and closed the fuel supply during the descent. The aircraft landed successfully on runway 34 and taxied off the runway to the left. There were no injuries resulting from the incident.
The investigation
The ÚZPLN investigation focused on the technical failure of the engine components. Examination of the aircraft revealed damage to the engine cowling, which had been burned through by hot exhaust gases. The investigation also found that both the inner and outer shells of the exhaust muffler and the heat exchanger had been damaged. Specifically, the heat exchanger for the cabin heating was destroyed.
Technical records showed that a 50-hour inspection had been performed on the aircraft on May 4, 2018, at which time no defects were found in the exhaust or heat exchanger. The investigation confirmed that the exhaust and heat exchanger were correctly installed and that the aircraft and pilot were fully compliant with all necessary documentation and certifications.
Findings
- The engine exhaust muffler casing failed due to operational wear and vibrations caused by thermal cycling (changes in thermal loading).
- The failure of the muffler casing allowed hot exhaust gases to escape into the engine compartment, where they ignited the carbon fiber cowling.
- The fire was extinguished by the airflow during flight.
- The pilot responded correctly and followed the procedures outlined in the aircraft flight manual.