What happened
On December 19, 2014, a Cessna 172F, registration CS-AKH, departed from Santarém airfield (LPSR) for Coimbra. After landing in Coimbra to reposition, the aircraft was prepared for a return flight to Santarém. The crew, consisting of two pilots and one passenger, departed Coimbra at approximately 16:40 UTC without performing an engine stop or any external inspections.
Roughly 15 minutes into the flight, the engine began exhibiting abnormal behavior, characterized by severe vibrations and a significant power loss, with RPM dropping to a maximum of 1500. As engine oil pressure continued to decline, the pilot determined that the aircraft could not reach the intended destination and initiated an emergency landing at a field near Pombal (PT-0033 Casalinho). The aircraft, configured with full flaps, struck the ground violently at low airspeed and came to a stop in an inverted position. While the crew and passenger sustained minor injuries, the aircraft suffered substantial damage to the nose gear, powerplant, fuselage, and wings.
The investigation
The GPIAAF investigation focused on the engine's lubrication system and the sequence of events leading to the power loss. Investigators identified traces of engine oil spilled along the lower fuselage. Analysis of the engine components and the impact site revealed that the engine was not rotating at the moment of impact, and one propeller blade was bent. The investigation also examined the maintenance history, noting the aircraft had completed a 200-hour/annual inspection in September 2014, and reviewed the crew's decision-making process regarding the transition from a precautionary to a forced landing.
Findings
- The primary cause of the engine failure was a loss of engine oil due to a failure in the lubrication system.
- The pilot did not recall observing the engine oil temperature indicator during the flight.
- The decision to depart Coimbra without a post-landing inspection or engine shutdown may have prevented the detection of early signs of oil loss.
- Pressure to complete the flight before sunset may have contributed to the rushed turnaround in Coimbra.
- The crew's transition from a precautionary landing attempt to a forced landing was necessitated by the inability to maintain sufficient energy to reach an airfield.