What happened
On May 4, 2012, at approximately 23:55 local time, a Piper PA 28-235 Cherokee D, registration YL-MED, was conducting a VFR training flight near Tartu, Estonia. The aircraft was occupied by an instructor and two student pilots. During approach maneuvers to runway 26, the aircraft was approximately 6 miles east of the airfield when the instructor noticed the oil pressure dropping to zero.
As the aircraft turned back toward the airport, the smell of burning oil entered the cockpit, and engine power began to decline. The instructor took control from the student pilot as the engine became irregular and eventually ceased functioning at an altitude of approximately 1,000 feet. Attempting to land in the darkness, the pilot directed the aircraft toward a field. The aircraft struck a hillside, bounced twice, and came to rest in a ditch.
The investigation
The Estonian Safety Investigation Bureau examined the wreckage and the engine components. Investigators found significant damage to the airframe, including destruction to both wings, a broken left landing gear, and damage to the engine and propeller. The underside of the fuselage and the horizontal stabilizer were covered in oil residue.
Microscopic analysis of the oil hose connection between the oil pump and the radiator was performed. While no defects or evidence of improper installation (such as over-tightening) were found on the threads, investigators determined that the connection had become disconnected during flight. The investigation noted that while the last major maintenance occurred 120 flight hours prior, there was no evidence of leaks during the pre-flight inspection.
Findings
- The primary cause of the accident was the disconnection of the oil hose connection leading to the radiator, which resulted in a rapid loss of oil pressure and subsequent engine failure.
- The engine showed signs of overheating, evidenced by blue discoloration on the cylinders.
- The disconnection likely progressed due to engine vibrations during flight.
- The crew and students sustained light injuries.