What happened
On January 23, 2011, a Robinson R-22 helicopter, registration PT-YDW, was conducting an instructional flight from Belém Novo to Santa Cruz do Sul. Approximately ten minutes after takeoff, while crossing the Guaíba River at 500 feet, the crew experienced intense vibrations and a noticeable change in engine noise. Following a slight left yaw and the activation of low RPM alarms, the instructor attempted to return to the departure airfield. Realizing the flight could not continue, the instructor executed an autorotation, performing an emergency landing on the banks of the river. The two occupants, an instructor and a student, sustained minor injuries, but the aircraft suffered severe damage to the engine, rotor blades, tail cone, and airframe structure.
The investigation
CENIPA investigators examined the engine and its components following the accident. Upon disassembly of the Lycoming engine, technicians discovered a significant accumulation of metal shavings (swarf) within both the oil filter and the oil pan. The investigation revealed internal damage to the engine block, including cracks near cylinder number 3 and damage to the cylinder heads and piston. Evidence showed that the engine had been experiencing excessive oil consumption, averaging approximately one liter every two hours of flight. Furthermore, investigators found that these oil top-ups were not being recorded in the aircraft's maintenance logbook, which is a violation of established aviation regulations.
Findings
- Excessive oil consumption and the failure to implement manufacturer-recommended corrective maintenance measures.
- Internal engine wear characterized by metal debris in the oil system, which led to the loss of power.
- Inadequate maintenance supervision, as the lack of proper documentation for oil replenishment went unnoticed by the flight school's management.
- The engine was approaching a scheduled overhaul, which may have contributed to the lack of immediate intervention for the high oil consumption.