What happened
On September 28, 2014, a Maule MX-7-235, registration HB-KCE, was performing a glider tow operation at St. Gallen-Altenrhein Regional Airport. After a successful initial tow, the pilot prepared for a second takeoff, towing a Janus-C glider, registration **HB-156 and a passenger. Shortly after takeoff, as the aircraft reached approximately 50 meters above ground level near the end of the runway, the engine suddenly lost power and stopped.
The glider pilot immediately released the tow rope and performed a safe landing on a grass runway. The pilot of the HB-KCE declared a MAYDAY and executed an emergency descent. During the landing on a grass area between the paved runway and taxiway SIERRA, the tow rope snagged on a runway edge light, causing the rope to snap and causing minor damage to the lighting fixture. The aircraft came to a stop approximately 12 meters from the airport perimeter fence. While the pilot escaped the aircraft due to the smell of fuel, no injuries were reported among the crew or the two people on the ground.
The investigation
Investigators examined the engine and exhaust system of the HB-KCE. The technical inspection revealed that a component known as the flame tube (or flame cone) within the main silencer of the exhaust system had broken into two pieces. One half of the tube had shifted into the exhaust tailpipe, effectively blocking the exit for exhaust gases.
Maintenance records showed that the aircraft had undergone a 50-hour inspection in June 2014. During that inspection, the exhaust system was checked visually using a flashlight, but no defects were found. A more thorough inspection of the silencer was not required until the upcoming 100-hour/annual inspection scheduled for October.
Findings
- The primary cause of the engine failure was an exhaust blockage caused by the structural failure of the flame tube.
- The broken fragment of the flame tube obstructed the tailpipe, preventing proper gas expulsion and leading to a rapid loss of engine power.
- The tow rope snapped during the emergency landing after catching on a runway light, causing minor damage to the airport infrastructure.