What happened
On October 22, 2013, an AS 350 B2 helicopter, registration PR-GPM, was performing a flight from the vicinity of Rio de Contas to Mucugê, Bahia, operated by the Bahia State Public Security Secretariat. The aircraft was carrying two crew members and three passengers. During the final approach to landing, at an indicated airspeed of 5/0 knots and an altitude of approximately 100 feet, the engine suffered a sudden loss of power. This was accompanied by the activation of the low rotor RPM warning horn. The pilot executed an autorotation, resulting in a forced landing on a dirt road. While the aircraft sustained substantial damage—including broken landing skids, a ruptured fuselage below the cockpit, and a bent tail boom—all five occupants escaped without injury.
The investigation
CENIPA investigators examined the engine, the fuel system, and the refueling equipment used prior to the flight. The investigation focused on the Fuel Control Unit (FCU) and the fuel samples collected from both the aircraft and the refueling truck (CTA) used by the operator. Investigators found that the engine's compressor was experiencing difficulty rotating with an audible friction noise. Upon disassembly, the investigation revealed that the metering valve within the FCU had become stuck in the closed position. Chemical analysis of the fuel samples from the aircraft and the refueling truck identified a viscous contaminant, specifically sodium polyacrylate, which had caused the valve to seize.
Furthermore, the investigation looked into the maintenance and operational procedures of the refueling truck. It was noted that the manufacturer's recommendations for the fuel filters were written in English, a language that the refueling personnel were not proficient in. Additionally, the refueling truck lacked a differential pressure gauge, making it difficult to monitor the condition of the fuel filters.
Findings
- The engine power loss was caused by the FCU metering valve becoming stuck in the closed position due to contamination by sodium polyacrylate.
- The contaminant was present in both the aircraft fuel and the fuel from the refueling truck.
- The refueling truck was not equipped with a differential pressure gauge to monitor fuel filter performance.
- Personnel involved in refueling operations lacked sufficient familiarity with the manufacturer's technical recommendations due to language barriers.
- Management oversight failed to identify deficiencies in training and English language proficiency for ground support personnel.