What happened
On April 14, 2008, a PIPER PA-28R-200, registration EC-FHZ, departed from Cuatro Vientos Airport for a two-hour instructional flight. The aircraft was occupied by an instructor and two students. During the cruise phase of the flight near El Tiemblo, the crew observed a sudden increase in engine speed accompanied by a drop in propeller pitch, followed by a burnt smell in the cabin. The engine subsequently failed.
Unable to restart the engine, the instructor attempted an emergency landing. Due to the low altitude and the rugged, wooded terrain, the pilot was unable to locate a suitable field. The aircraft struck the top of a large pine tree, which absorbed much of the impact energy, before falling to the ground. All three occupants sustained serious injuries.
The investigation
The investigation focused on the mechanical failure of the Lycoming IO-360-C1C engine and the subsequent crash dynamics. Metallurgical analysis of the engine revealed that the crankshaft had undergone a fatigue fracture. This fracture was traced back to excessive bending loads caused by the improper installation of the crankshaft's central support half bearings, which were mounted outside of their positioning tabs.
Investigators also examined the engine's maintenance history. They found that the overhaul procedures did not adhere to the manufacturer's approved methods. Specifically, evidence of excessive sealing material was found on the through-studs and at the base of the no. 3 cylinder, suggesting that previous maintenance attempts had focused on masking an oil leak rather than correcting its underlying cause. Furthermore, the aircraft's emergency locator transmitter (ELT) was inoperative because its battery had exceeded its service life and it had not been properly maintained.
Findings
- The primary cause of the accident was the in-flight fatigue fracture of the crankshaft resulting from the improper installation of the central support half bearings.
- Improper engine overhaul practices and inadequate subsequent maintenance contributed to the failure.
- Maintenance efforts had attempted to alleviate an oil leak at the no. 3 cylinder using sealant rather than following manufacturer-approved repair instructions.
- The inoperative ELT and the lack of radio contact with ATC due to terrain-related signal limitations hindered the rapid location of the wreckage.
- Coordination among the various emergency and rescue services involved was found to be inefficient.