What happened
On March 22, 2025, at approximately 11:00 local time, a Cessna 152 departed from Purranque Aerodrome (SCPR) for a scheduled standardization flight. The crew, consisting of a private pilot and a flight instructor, was operating under Visual Flight Rules (VFR) with a planned stop at Cañal Bajo Aerodrome (SCJO).
Following takeoff from SCJO, while en route back toward Purran and heading toward the original destination, the aircraft experienced a progressive loss of engine power, characterized by a noticeable drop in engine revolutions (RPM). Faced with the deteriorating engine performance, the pilot executed an emergency landing in a flat agricultural field in the Chahuilco sector, within the commune of Río Negro. Despite the forced landing, there were no injuries to the two occupants, and the aircraft sustained no damage.
The investigation
DGAC Chile investigators examined the aircraft and the maintenance history of the operator, a certified flight club. Maintenance records indicated that the aircraft had undergone an annual inspection just 20.2 hours prior to the event. This inspection included checks of the fuel system, air filter, and carburetor, with no discrepancies noted at that time.
Upon inspecting the aircraft at the landing site, investigators found the engine oil level was within limits and no external leaks were present. However, ground functional tests revealed that the engine could not exceed 1,200 RPM, significantly below the normal operating range of 1,900 to 2,550 RPM. The engine exhibited symptoms of an excessively lean mixture. While the use of primer temporarily increased RPM to 1,600, the power loss persisted.
To isolate the issue, investigators replaced the original carburetor with a serviceable unit. Following this replacement, the engine successfully reached 2,300 RPM, and all other parameters, including magneto drop and oil pressure, returned to normal operating ranges.
Findings
- The primary cause of the engine power loss was the presence of charcoal and foreign material found within the carburetor's mixture metering valve and injector.
- Fuel samples taken from both wing tanks were clear of water or sediment and were confirmed to be the correct grade (100 LL).
- The engine's air intake, oil levels, and spark plugs were all found to be in normal condition.