MOSCOW (AP) — Russian investigators are combing through the charred fragments of a Boeing 737 jetliner that crashed and killed all 50 people on board.

The plane belonging to the Tatarstan Airlines crashed Sunday while trying to land at its home port in the Russian city of Kazan.

Kazan is the capital of the oil-rich province of Tatarstan. The son of the provincial governor was among the victims.

The head of the local branch of Russia’s Investigative Committee says the plane crashed while making a second attempt at landing. He says investigators are trying to determine why the crew couldn’t land the first time, and investigators are looking into a possible pilot error or an equipment failure.