What happened
On January 28, 2018, a Robinson R44 II helicopter, registration PT-FJS, operated by Ultra Pilots Taxi Aéreo Ltda, departed from Jacarepaguá Aerodrome (SBJR) in Rio de Janeiro, bound for Helicentro Guaratiba (SJGK). During the initial climb, shortly after passing 600 feet, the pilot observed significant oscillations on the engine tachometer, followed by a drop in rotor RPM.
In an attempt to stabilize the aircraft, the pilot manually applied power to override the governor. However, the oscillations and RPM drops recurred twice more. Believing an engine failure was imminent, the pilot decided to execute an autorotation. The pilot directed the aircraft toward a flat area of uneven terrain. During the landing sequence, the pilot performed a flare that caused the aircraft to slide and eventually capsize after one of the skids struck an irregularity in the ground. The pilot sustained minor injuries, but the aircraft suffered substantial damage.
The investigation
CENIPA investigators examined the engine, magnetos, governor, and fuel system, finding no evidence of mechanical engine failure; the engine remained operational throughout the entire event and continued running after the capsize. Ground simulations demonstrated that electrical contact failures could indeed cause the observed tachometer and rotor RPM oscillations.
The investigation focused on the wiring connections between the right magneto and the tachometer/governor. It was discovered that the maintenance of these connectors did not comply with Robinson Helicopter Company Service Letter 47. While the service letter instructed the use of three cable ties (two transverse and one longitudinal) to prevent wire damage, the aircraft was found with only two transverse ties. This improper securing allowed for the intermittent electrical contact that triggered the false indications of low RPM.
Findings
- Improper maintenance of the electrical connectors, specifically the failure to install the third longitudinal cable tie as required by Service Letter 47.
- Inadequate pilot decision-making, as the pilot executed an unnecessary autorotation despite the engine remaining functional and the lack of actual engine failure symptoms (such as left-hand yaw or oil pressure loss).
- Inaccurate interpretation of instruments, where the pilot failed to recognize that the oscillations suggested a governor issue rather than a total engine failure.
- Inadequate training or knowledge regarding the specific emergency procedures for governor failure in the R44, which include manual power control via the collective switch.
- Contributing factors including the pilot's relatively low experience in the model (120 hours) and the stress of managing multiple variables during the climb.