What happened
On July 19, 2008, a Sikorsky S-61N, registration N91158, was performing a scheduled flight sequence near the Echarate district in Cusco, Peru. The aircraft, operated by AeroMaster del Perú S.A.C., was transporting 11 passengers and two crew members to the K7 Traza Cashiari remote helipad.
During the final approach to the landing site, the co-pilot attempted to adjust the main rotor RPM. Despite increasing the power to full, the rotor RPM continued to decrease. The pilot responded by reducing collective pitch and pushing the cyclic forward in an attempt to reach the landing platform. However, the aircraft lost control and struck the ground approximately 11 meters outside the landing pad. The impact caused damage to the right main landing gear, the tail skid, and the lower right side of the fuselage. While there were no fatalities, one passenger sustained neck pain, and the crew successfully evacuated the aircraft.
The investigation
The CIAA investigation examined the aircraft's maintenance records, flight data from the cockpit voice recorder, and the crew's performance. The investigation confirmed that the engines, transmission, and rotor components were in airworthy condition and that the aircraft's weight and balance were within limits.
Investigators analyzed the crew's communication and training. It was noted that the pilot instructor, a New Zealander, had limited proficiency in Spanish, while the co-pilot was undergoing flight instruction. The investigation also reviewed the company's operational manuals and the crew's adherence to approach checklists and briefing procedures.
Findings
- The primary cause of the incident was the loss of aircraft control during approach due to an undetected power settling (vortex ring state) phenomenon.
- Ineffective communication between the crew members, caused by the instructor pilot's limited command of the Spanish language, hindered the recognition of the aerodynamic instability.
- The crew failed to follow the aircraft's operational manual regarding standard flight procedures.
- The company failed to conduct a proper pre-approach briefing as required by its General Operations Manual (MGO).