Introduction
An analysis of engine parameters was conducted as part of the investigation into an accident involving a Robinson R-66 helicopter, registration RA-05783. The report, issued by the Interstate Aviation Committee, details the behavior of the engine during the event.
Engine Performance During Initial Phases
According to the report, the engine functioned normally during start-up, ground idle, transition to flight idle, and initial load increase. Parameters such as compressor speed and gas temperature showed smooth and corresponding changes.
Power Turbine Oscillations
Prior to an overshoot of power turbine speed (N2), cyclic oscillations of N2 were observed. Given the smooth changes in compressor speed and gas temperature, it is likely that these oscillations were generated by an external influence.
Power Reduction and Load Removal
The observed power reduction was associated with a downward deflection of the collective lever. Despite the reduced power turbine speed, compressor speed did not increase. Subsequently, a sharp increase in power turbine speed occurred due to load removal. The control system response was consistent with the activation of power turbine overspeed protection.
Stabilization
After the overspeed was halted, the compressor was at or near ground idle, and the power turbine speed stabilized, indicating the absence of load.
Organizational Background
The report includes information about the operator. Originally established in 1956 as Turin Aviation Enterprise, it was renamed to Evenkia-AVIA in 2002, and then to KrasAvia in 2007. KrasAvia operates over 50 aircraft and holds a certificate of operation.