What happened
On October 16, 2001, a Cessna 172N, registration EC-EJG, was conducting a dual-instruction flight from Córdoba Airport to Sevilla Airport. While flying near Posadas, Córdoba, at an altitude of approximately 2,000 feet, the aircraft experienced a sudden loss of engine power. The instructor initially attempted to return to the departure airport and notified Sevilla Control; however, as the aircraft continued to lose altitude, the pilot determined that reaching Córdoba was not possible.
The pilot initiated an emergency landing in a field that appeared clear of vegetation, cables, or obstacles. During the landing roll, the nose gear struck a transverse irrigation pipe. The impact caused the nose gear to collapse, leading the aircraft to nose over and come to rest in an inverted position. Both occupants of the aircraft were uninjured.
The investigation
Investigators examined the engine at the crash site and discovered that a spark plug in cylinder number 3 had been dislodged from its housing. The investigation revealed that a heli-coil insert, which had been installed to repair the spark plug thread, had detached along with the plug.
Maintenance records showed that a previous repair had been performed using a heli-cut to address a loose thread. Following a 50-hour engine inspection, the pilot had noted the thread issue and, following the Lycoming Overhaul Manual, installed a new heli-coil with a diameter 0.010 inches larger. At the time of the accident, the aircraft had flown 166 hours and 15 minutes since the installation of this second heli-coil.