What happened
On December 21, 2020, at approximately 18:50 local time, a Piper PA-28-160 Cherokee was conducting a flight instruction mission near the Curacaví Aerodrome (SCCV) in Chile. The aircraft, operated by a flight instructor accompanied by a student pilot, departed the aerodrome at 18:35 local time following a successful pre-flight inspection.
While cruising at an altitude of 1,900 feet, the aircraft's engine experienced a sudden loss of power. In response to the engine failure, the instructor performed an emergency landing in an agricultural field located approximately two kilometers north of the aerodrome. Despite the impact, both occupants remained uninjured, and they were able to evacuate the aircraft on their own. The aircraft sustained no significant structural damage, though the engine was found to have internal components compromised.
The investigation
DGAC Chile investigators examined the aircraft, the engine, and the environmental conditions at the time of the occurrence. The investigation included a physical inspection of the Piper PA-28-160 Cherokee and its Lycoming O-320-B2B engine.
Technicians inspected the engine cylinders and found that while cylinders 1, 2, and 4 showed satisfactory compression, cylinder number 3 lacked compression entirely. Upon disassembling the third cylinder, investigators discovered that the piston head was fractured with a loss of material near the compression ring junction. The fracture area showed signs of erosion and exposure to extreme heat. Additionally, the engine's exhaust muffler exhibited internal deformations, which were attributed to high-temperature exhaust gases.
Maintenance records indicated that the aircraft had undergone its annual and 100-hour inspection on September 14, 2020, just 26.59 flight hours prior to the accident. The inspection had previously confirmed satisfactory differential compression across all cylinders. Fuel samples taken from the site were confirmed to be standard AVGAS 100LL.
Findings
- The engine experienced a fracture of the piston head in cylinder number 3.
- Evidence of overheating was present on the valve cover and spark plugs of cylinder number 3.
- The aircraft was not equipped with Exhaust Gas Temperature (EGT) or Cylinder Head Temperature (CHT) indicators, meaning the crew had no real-time way to monitor these thermal parameters.
- The investigation noted that high-power operations can lead to detonation, a phenomenon where uncontrolled combustion causes rapid pressure and temperature spikes, which can result in the exact type of piston damage observed.