What happened
On December 6, 2008, a Eurocopter SA 315B, registration OB-1801-P, operated by Helinka S.A.C., was performing a VFR transport flight from Nazca to Cusco. While cruising at 14,500 feet over the Tintay area in the Apurimac region, the pilot reported hearing three continuous detonations. Following these sounds, the aircraft experienced a significant change in heading, a moderate left bank, and an uncontrolled descent accompanied by heavy vertical vibrations.
During the emergency, the right-side cabin door opened, causing a piece of luggage to fall from the aircraft. The pilot attempted to maintain control of the aircraft to avoid mountainsides, power lines, and dwellings. As the engine RPM dropped to 20,000 and the main rotor RPM fell to 340, the pilot executed an autorotation and a 180-degree turn, ultimately performing a forced landing in a peach orchard at an altitude of approximately 8,700 feet. The pilot and a passenger (a mechanic) survived the impact, though the mechanic sustained a spinal injury.
The investigation
The CIAA investigation focused on the sequence of events leading to the loss of control. The investigators examined the engine performance, the aircraft's maintenance history, and the crew's training programs. The investigation established that the Turbomeca Artouste III B1 engine suffered an intermittent compressor stall. The investigators also reviewed the company's training manuals and the installation of the Emergency Locator Transmitter (ELT).
Findings
- The primary cause of the accident was the loss of control of the helicopter due to a decrease in main rotor RPM, triggered by an engine compressor stall.
- The crew failed to correctly identify and respond to the engine emergency in a timely manner; the pilot likely misidentified the compressor stall as a general mechanical failure.
- The operator's training program did not include instruction regarding the phenomenon of intermittent or continuous compressor stalls.
- The crew's emergency response was delayed and insufficient to prevent the descent into the terrain.
- The behavior of the mechanic, who attempted to close the cabin door during the emergency, likely distracted the pilot from managing the engine failure.
- The ELT was not installed according to the manufacturer's specific recommendations.
- The transport of 20 gallons of additional fuel in external baskets constituted the transport of dangerous goods under IATA regulations.
Safety action
- The DGAC was advised to review helicopter operator training programs (under RAP Part 135) to include information on mountain aerology and compressor stall recovery.
- The DGAC and the operator were advised to ensure ELT equipment is installed according to manufacturer specifications.