What happened
On March 1, 2020, a Robinson R22 helicopter, registration PT-HVQ, was conducting a flight training mission for a Commercial Pilot Helicopter (PCH) program. The flight originated from Aeródromo João Monteiro in Vila Velha, Espírito Santo, with an instructor and a student on board.
During the return leg of the flight, while descending through 2,700 feet after crossing a mountain range, the crew heard an unusual noise followed by a complete engine failure. The instructor took control of the aircraft and executed an emergency autorotation, successfully landing the helicopter in a rural, open area. While the pilots escaped the incident without injury, the aircraft sustained substantial damage.
The investigation
CENIPA investigators examined the engine, the fuel, and the maintenance records of the aircraft. Physical inspections of the Lycoming O320-B2C engine revealed that cylinder number 2 had lost compression. The investigation identified severe wear on the exhaust valve of that cylinder, which caused improper seating and allowed the air-fuel mixture and combustion gases to leak, preventing the engine from producing necessary work.
Investigators also found water inside the carburetor bowl and within cylinders 2 and 4, along with oxidation on the spark plugs of those cylinders. Although the fuel samples themselves were clear and free of water, the atmospheric conditions at the time—specifically a temperature of 30°C and a dew point of 24°C—were highly conducive to carburetor icing. Notably, the aircraft's carb heat control was found in the 'off' position at the time of the accident.
Furthermore, the investigation scrutinized the maintenance history. It was discovered that mandatory maintenance tasks, specifically Textron Lycoming Service Instruction nº 1191A and Service Bulletin nº 301B, had not been documented as completed in the aircraft's primary records for a significant period. The engine had flown over 400 hours without the specific inspections required by these instructions.
Findings
- The engine failure was likely caused by a combination of mechanical wear on the exhaust valve and potential carburetor icing.
- Maintenance records showed a failure to comply with mandatory Service Instruction nº 1191A and Service Bulletin nº 301B regarding cylinder and valve inspections.
- Meteorological conditions were favorable for carburetor ice formation, and the carb heat was not engaged during the descent.
- The pilots were properly licensed, qualified, and the aircraft was within weight and balance limits with a valid airworthiness certificate.