A Russian Mi-8 helicopter crash-landed in northwestern Siberia, killing 19 people and injuring three others, according to reports Saturday. The chopper was flying oil and gas field workers when the accident happened.

The crash occurred Friday and officials reportedly recovered the helicopter’s two black boxes.

“Rescuers that arrived at the site have entered the damaged helicopter, where they found three people in serious condition. According to preliminary date, other 19 passengers were killed,” a local law enforcement source told Tass news agency on Saturday.

According to reports, a survivor trapped in the wreckage called rescuers through a cell phone. About 140 people were reportedly involved in rescue mission.

Three of the dead were helicopter crew members and rest were oil-industry workers. Russian President Vladimir Putin expressed condolences to families of the victims.

The helicopter was manufactured in 1984 and had a flight safety license valid till 2017, according to Russia’s civil aviation authority. Officials have launched an investigation into the crash.

“The investigation deals with three main versions of the crash of the aircraft: a violation of the rules of operation and flight safety, equipment failure, and adverse weather conditions. None of these is so far regarded as most likely,” the Investigation Committee said in a statement.