What happened
On July 4, 2017, at approximately 15:45 local time, a private Cessna 206H, registration CP-2442, departed San Lorenzo for Cochabamba under Visual Flight Rules (VFR). While approaching Cochabamba, the pilot notified air traffic control of a potential engine failure due to overheating. After being cleared for an approach to runway 22, the pilot declared an emergency at 16:48, reporting engine issues and attempting to restart the engine at 11,000 feet.
The aircraft was unable to maintain flight and entered a low-speed glide/stall condition. During the descent, the main landing gear struck electrical cables on an adjacent avenue, causing a utility pole to collapse. The aircraft then struck the perimeter fence of a nearby park before impacting the ground with its nose gear. The impact caused the nose gear to fracture and detach. The aircraft slid 35 meters across the terrain before coming to a stop. The pilot, who was the sole occupant, evacuated the aircraft without injury.
The investigation
The Bolivian DGAC-AIG investigation focused on the mechanical state of the engine and the maintenance history of the aircraft. Investigators examined the engine cylinders, found evidence of overheating in several cylinders (numbers 3, 4, 5, and 6), and noted that cylinder number 4 showed signs of barrel separation and combustion gas leakage.
Laboratory analysis of the engine oil revealed critical levels of metallic wear particles, including iron, chromium, nickel, copper, lead, and aluminum. Furthermore, the investigation found that the magnetos were out of synchronization, with the timing set at 28 degrees instead of the standard 20 degrees. The inspection also noted that the right fuel tank was empty, while the left tank contained 20 gallons.
Findings
- Engine overheating caused by friction in the power block components and significant wear/pitting on the camshaft lobes.
- Severe engine oil contamination containing high concentrations of metallic debris (iron, lead, etc.).
- Improper magneto synchronization, contributing to the thermal issues.
- Fuel exhaustion in the right fuel tank.
- Maintenance deficiencies, specifically a lack of documented component replacements in the engine logbook following its overhaul.
- Inadequate air traffic control prioritization, as the controller did not immediately clear traffic to allow the distressed aircraft a direct path to the runway.