What happened
On September 24, 2004, a Robinson R-44 helicopter, registration PP-MJR, was conducting a filming mission for a television network. Approximately 15 minutes into the flight, while over the Playcenter area in São Paulo, the aircraft experienced a sudden engine RPM surge that was not accompanied by a corresponding increase in main rotor RPM.
In response to the engine malfunction, the pilot attempted to recover the aircraft before deciding to perform an emergency autorotation onto an unprepared area. During the landing, the aircraft struck the ground with significant force and at an angle. The impact caused the main rotor to strike the ground and resulted in the rupture of the tail cone. Despite the severe damage to the airframe, the pilot and two passengers escaped without injury.
The investigation
CENIPA investigators focused their technical analysis on the power transmission components to determine why the engine RPM surged without affecting the main rotor. The investigation revealed several critical discrepancies regarding the aircraft's maintenance and configuration.
Technicians found that the electrical motor for the actuator was covered in a PVC shroud and was consuming approximately 8.0 A of current to start, far exceeding the normal 1.5 A. Additionally, a fuse installed in the actuator's circuit was 10 A, which was 6.5 times larger than the required 1.5 A specification. Evidence of unauthorized maintenance was also discovered, including unapproved paint touch-ups on the actuator assembly bolts.
The investigation further established that the aircraft was operating with several unapproved electronic modifications, including a GPS, filming lights, and monitors, which had not been certified by the aviation authority. Furthermore, the aircraft was carrying a flight manual belonging to a different helicopter (PP-MPR), and the lack of weight and balance records meant the center of gravity could not be accurately calculated.
Findings
- The primary cause of the engine malfunction was the power transmission system operating outside of manufacturer specifications due to the installation of non-airworthy components and unauthorized maintenance.
- The pilot exercised poor judgment by proceeding with the flight despite experiencing irregular engine start procedures that required resetting circuit breakers to prevent the motor from cutting out.
- The aircraft was being operated in a highly critical 'newscopter' mission profile, which involves high-stress hovering maneuvers that increase engine wear.
- Maintenance oversight allowed the aircraft to fly with unapproved electrical modifications and unverified maintenance practices.