What happened
On November 23, 2019, a Cessna C207, registration OB-2136, operated by Aerolineas Brag S.A.C., was conducting a scheduled tourist flight over the Nazca Lines in Ica, Peru. After departing from Nazca "María Reiche" (SPZA) airfield, the aircraft was climbing through approximately 2,500 feet while performing maneuvers near the "Whale" geoglyph. During a right-hand turn, the crew experienced sudden power oscillations and a severe reduction in engine power to minimum levels, resulting in a rapid loss of altitude.
The pilot declared an emergency and identified an agricultural field in the "Achaco Bajo" area for an emergency landing. During the approach, the crew had to fly beneath a medium-voltage electrical cable to reach the landing site. The aircraft touched down in the field and came to a stop after approximately 250 meters. There were no injuries to the two crew members or the six passengers on board. The aircraft sustained minor damage to the lower fuselage and tail skid.
The investigation
The CIAA investigation focused on the engine's performance and maintenance history. Investigators examined the engine, which is a Continental Motors IO-520F, and inspected the spark plugs. The investigation revealed that the engine was experiencing significant vibrations during test runs.
Maintenance records showed that the aircraft had undergone a 100-hour inspection on October 19, 2019, and was only 31 hours into its next inspection cycle at the time of the incident. While the operator's maintenance program required spark plug inspections every 100 hours, the manufacturer's recommendations for the Champion spark plugs suggested more frequent checks for contamination and gap calibration.
Findings
- The primary cause of the incident was a partial loss of engine power caused by the poor condition of five of the twelve spark plugs.
- The faulty spark plugs, located in cylinders #1, #4, and #5, exhibited severe electrode wear, ceramic insulator damage, improper gap calibration, and contamination from oil, carbon, and lead.
- This degradation disrupted the engine's firing order, significantly reducing engine performance during a high-power climb phase.
- The operator's maintenance program failed to follow the manufacturer's recommendation to inspect spark plug gaps and deposits every 50 hours.
- There was inadequate oversight by the operator regarding the maintenance performed by the contracted maintenance organization, which failed to detect the deteriorating state of the components.