What happened
On June 22, 2007, at 13:20 local time, a Robinson R-44 Raven, registration EC-JDT, was conducting an aerial observation mission near Puerto de Malagón, Madrid. The flight, operated by Intercopters, S. L., was carrying two qualified pilots and two police officers undergoing training.
The aircraft was performing an approach to a flat area of terrain to allow the observers to swap seats. During this phase, while flying at a pressure altitude of 5,100 ft and an indicated airspeed of approximately 30 KIAS, the pilot received both acoustic and visual warnings indicating low main rotor RPM. In an attempt to recover, the pilot lowered the collective lever and tried to increase airspeed to perform a running landing. However, the helicopter descended and struck the ground, subsequently rolling onto its right side.
There were 4 fatalities (two crew members and two passengers) resulting from the impact.
The investigation
The investigation focused on the aircraft's performance at high altitude and the pilot's response to the low RPM warning. The aircraft was found to be in good maintenance condition, with a valid Certificate of Airworthiness.
Investigators analyzed the flight weight, noting that at 5,100 ft, the aircraft's weight of approximately 2,324 lb was near the maximum limit for hover-out-of-ground-effect (HOGE) conditions. The investigation also examined the functionality of the electronic governor. While the aircraft was equipped with a governor to manage engine power, the flight manual specifies that at altitudes above 4,000 ft, the governor's effectiveness is significantly reduced, requiring the pilot to manually manage the throttle to maintain rotor RPM.
Findings
- The aircraft was operating at a high power requirement due to its high altitude and weight, which was near the maximum allowable limit.
- The pilot, while highly experienced in turbine-engine helicopters, had only 200 hours of experience in the Robinson R-44 Raven.
- The pilot likely failed to immediately increase the throttle following the low RPM warning, as recommended by safety notices.
- The loss of airspeed during the approach likely caused an increase in the blade angle of attack to maintain lift, which, combined with insufficient power application, led to a decay in rotor RPM and a subsequent rotor stall.