What happened
On March 3, 2023, a Cessna 172G, registration OB-1100, operated by Servicios Aéreos Ruiz E.I.R.L., was performing a scheduled flight from San Lorenzo to Bellavista to collect passengers. While cruising at 1,500 feet, approximately 13 nautical miles from San Lorenzo, the pilot experienced a sudden drop in engine RPM and a noticeable change in engine sound.
Following the engine malfunction, the pilot declared an emergency via radio, intending to land at the Jeberos landing strip. During the descent, oil began leaking from the engine, spraying onto the windshield and progressively obscuring the pilot's forward vision. With the windshield covered in oil, the pilot attempted to maintain alignment with the runway by relying on vision through the left side window.
Upon contacting the runway, the aircraft lost directional control and struck nearby bushes. The aircraft then veered off the left side of the runway (runway excursion) and subsequently overturned (capsized). The pilot sustained minor injuries and was able to exit the aircraft on his own. The aircraft suffered severe damage.
The investigation
The CIAA investigation examined the engine components and maintenance history. The engine had recently undergone an overhaul, having completed only 11.2 hours of operation since the service. Investigators found that during the engine disassembly, piston ring gaps were found to be outside of the limits specified in the manufacturer's overhaul manual, and the rings in cylinders No. 1 and No. 6 were nearly aligned, which contradicts recommended overhaul procedures.
Additionally, the investigation noted that the engine was transported from Yurimaguas to Lima using procedures that did not align with recommended standards for aviation engine transport. While the operator provided oil and fuel hoses for leak testing, investigators could not confirm if these were the same hoses used in the accident.
Findings
- The primary cause of the accident was a runway excursion during an emergency landing caused by a lack of directional visibility due to oil on the windshield, which was triggered by an engine oil leak and power loss.
- Contributing factors included unadjusted clamps or defective oil hoses that loosened or disconnected, leading to the leak and power loss.
- A deficiency in the pre-flight inspection prevented the detection of the improper state of the engine's oil clamps or hoses.