What happened
On January 1, 2019, a Robinson R44 II helicopter, registration PR-RMZ, was performing a scenic flight over Ubatuba, São Paulo, when it experienced a sudden loss of rotor RPM. Approximately 55 seconds after takeoff, while climbing at roughly 350 feet, the aircraft's low RPM horn and visual caution light activated.
Believing the engine had failed, the pilot initiated an autorotation procedure. During the descent, the helicopter struck utility pole wires and tree branches in an urban area. The impact with the ground caused the aircraft to strike several parked vehicles, including ten cars, and an apartment window. The accident resulted in one fatality (a pedestrian) and two serious/minor injuries among the occupants.
The investigation
CENIPA investigators examined the aircraft's engine and magneto systems to determine why the low RPM alarm triggered. While the engine performed normally during bench tests, investigators discovered lubricating oil residue inside the right-hand magneto.
Microscopic analysis of the magneto contact breakers revealed multidirectional scratches, suggesting that an inappropriate maintenance technique, such as using sandpaper, may have been used to clean the components. Laboratory tests confirmed that the presence of oil on these contact points could degrade the electrical signal sent to the governor and tachometer. This signal degradation caused the governor to malfunction, triggering the low RPM warning despite the engine still producing adequate power.
Findings
- Improper emergency response: The pilot initiated an autorotation based on the low RPM warning, whereas the correct procedure for a