What happened
On October 25, 2013, an R44 II helicopter, registration PR-MPL, was conducting a visual and photographic terrain survey over the Serra do Baixãozinho region in Sento Sé, Bahia. The flight originated from Petrolina, Pernambuco, with the pilot and two passengers on board.
While flying at approximately 400 feet AGL, the aircraft performed a maneuver on a heading of 120 degrees to move away from a local campsite. During this maneuver, the aircraft began to lose altitude, and the low rotor RPM warning horn sounded. Despite the pilot's attempt to lower the collective to recover engine RPM, the helicopter continued its descent and struck the ground, colliding with the vegetation of the caatinga. The impact caused substantial damage to the engine, main rotor, transmission, and airframe. The pilot sustained light injuries, one passenger suffered serious injuries, and the second passenger was uninjured.
The investigation
CENIPA investigators examined the wreckage and the aircraft's maintenance records. The investigation confirmed that the aircraft's airworthiness certificate was valid and that the 100-hour inspection had been completed recently. Analysis of the engine revealed that it was delivering rotational energy to the main rotor, ruling out mechanical failure as a cause.
The investigation also reviewed the aircraft's performance data. At the time of the accident, the aircraft was operating near its maximum takeoff weight for the prevailing atmospheric conditions (35°C). Investigators also considered the manufacturer's Safety Notice-34, which warns of the risks of losing translational lift during low-speed maneuvers at low altitudes.
Findings
- The pilot likely reduced the aircraft's airspeed to a level below the minimum required for maintaining translational lift while attempting to optimize the viewing angle for photography.
- A loss of situational awareness occurred as the pilot's attention was focused outside the cockpit on the terrain.
- The loss of translational lift led to a rapid decay in rotor RPM.
- It is possible that the pilot applied upward collective in an attempt to arrest the descent, which further contributed to the drop in RPM and made the collision unavoidable.