What happened
On February 7, 2011, at approximately 08:30 local time, a Robinson R22 Beta helicopter, registration HS-TZI, operated by the Civil Aviation Training Center, departed Hua Hin Airport for a training flight. The flight objectives included practicing maneuvers such as climbing, gliding, quick stops, and low passes.
While performing a low pass at an altitude of approximately 50 feet and a speed of 50 knots over the sea near Cha-am, Phetchaburi Province, the aircraft experienced an engine abnormality. The flight instructor noted that the engine RPM increased beyond normal limits while the main rotor RPM decreased, triggering a low rotor RPM warning. Although the instructor attempted to recover the aircraft by reducing engine power and increasing collective pitch, the insufficient altitude over the water prevented a successful recovery. The helicopter impacted the sea near the Baan Talay Samran resort at approximately 09:30 local time. Both the flight instructor and the student pilot sustained minor injuries and were able to exit the aircraft; the student swam to shore while the instructor was assisted by local residents.
The investigation
The investigation examined the aircraft's mechanical condition, the crew's performance, and adherence to safety protocols. Post-accident inspections of the engine revealed no mechanical defects in the cylinders, pistons, or crankshaft. However, investigators found traces of rust in the carburetor and noted that seawater and fuel had mixed within the fuel tank assembly. The airframe sustained significant damage, including a deformed cockpit, broken windshield, and a broken tail cone.
Findings
- The flight was conducted at an altitude of approximately 50 feet over water, which violated Robinson Helicopter Company's Safety Notice SN-19. This notice explicitly warns that flying low over water is hazardous and advises maintaining at least 500 feet above ground/water and avoiding operations below 200 feet.
- The primary cause of the accident was the failure of the flight crew to comply with the manufacturer's safety guidelines regarding minimum safe altitudes during over-water operations.