What happened
On July 7, 2016, a Robinson R44, registration RA-04371, was engaged in a multi-day flight across various regions of Russia. The aircraft, operated under the authority of LLC Fort-Ross, had previously traveled from the Leningrad region through several cities including Nizhny Novgorod, Yekaterinburg, Omsk, and Novosibirsk before reaching Krasnoyarsk.
Following a period of flight in the Krasnoyarsk region, the pilot and one passenger traveled to Lake Shunet in the Khakassia Republic for fishing. Later that same day, the pilot, the first passenger, and a second passenger departed from the Joyskaya Sosnovka area near the Sayano-Shushenskaya Dam to fly to the Kazyrsu River. The landing site for this final leg was selected by the pilot while in flight.
Prior to departing Joyskaya Sosnovka, the pilot used the onboard radio to notify the Abakan Air Traffic Control Center of the intended flight route and estimated time of arrival. However, upon arriving at the Kazyrsu River at 18:10, the pilot did not contact the Abakan center to report the completion of the flight.
The investigation
During the investigation, the pilot stated that the failure to notify air traffic control was due to radio signal shadowing caused by the mountainous terrain. The pilot maintained that the onboard radio equipment was functioning correctly and that he had verified its operational status prior to the flight.