Russian aviation investigators have commenced combing through a Boeing 737 wreckage near the city of Kazan Monday, after the plane crashed Sunday, killing all 50 passengers on board.

Flags flew at half mast in the city of 1.1 million, which is situated roughly 500 miles east of Moscow. The Kazan crash has raised new concerns over Russia’s poor aviation safety record, as the country prepares to host the Winter Olympics in the southern city of Sochi in February.

Tatarstan Airline Flight U363 exploded after going down at 15:25 GMT. The jet, which originated from Moscow Domodedovo airport, had been trying to abort its landing when it crashed. Transport Minister Maxim Sokolov said in a statement, “The plane just fell – (it) was vertical, practically vertical.” The jet’s nose reportedly hit the ground during touchdown.

Below is a clip of the crash:

Commenting on initial findings before an examination of the black box recorder, Alexander Poltinin, a senior regional investigator, said “The main versions are pilot error and technical problems, including equipment failure.” Poltinin added that the jet lost altitude quickly, and its fuel tank exploded when it hit the ground. The flames were extinguished several hours after the crash, though the Kazan Health Ministry reported that only two bodies had been found by noon on Tuesday. Poltinin said it could take weeks for all of the casualties in the wreckage to be identified.

According to the International Air Transport Association, Russia, along with the former Soviet republics, has one of the worst air-traffic safety records in the world, with a total incident count almost three times the world average in 2011.

Still, the Russian government says security and safety measures have been upgraded for the 2014 Sochi Olympic Games, and that city’s international airport has likewise been upgraded.

A new runway was built at the airport in Kazan, before the World University Games held in the city in July. Kazan is also one of the handful of venues hosting the soccer World Cup Russia in 2018.

Image via YouTube.