The Boeing 737 passenger plane has plunged vertically when it crashed and burst into flames Sunday afternoon, killing all onboard, while trying to touch down at the Russian airport of Kazan.

This was announced by Russia's Transport Minister Maxim Sokolov, the BBC reports Tuesday.

Citing witnesses of the crash, he has said that "the plane was vertical, practically vertical, but the [video] recordings aren't very high-quality because it was dark."

Investigators have found both of the flight recorders, or "black boxes". All 44 passengers and 6 crew died in the incident.

Tatarstan Airlines flight had been attempting a second landing in the city of Kazan when it crashed. Reports said the plane appeared to lose altitude before it caught fire.

Investigators are examining several possible causes - a technical malfunction, pilot error or poor-quality fuel. Terrorist attack has been ruled out. It was raining at the time but the weather conditions were favorable for landing, officials, cited by the BBC, say.

A spokeswoman for Tatarstan Airlines, Gulnaz Minnikhanova, stressed both pilots were very experienced and no technical problems had been reported with the plane before the flight.

Leading international media reported Monday that the 23-year-old plane entered service in 1990 and had several previous owners – French Euralair Horizons (now defunct), Air France, Uganda Airlines, Brazil's Rio Sul, Romania's Blue Air and lastly belonged to Bulgaria's national flag career, Bulgaria Air.

While in Brazil, it underwent a major repair after a non-fatal accident, according to The BBC.

After the Russian Emergency Ministry released the list of the dead, it emerged that Irek Minnikhanov, 23, son of Tatarstan President Rustam Minnikhanov, and Alexander Antonov, who headed the Tatarstan branch of the Federal Security Service, the main successor agency to the Soviet-era KGB, are among the fatalities.

Antonov has been accompanying newlywed Minnikhanov, who has married Frenchwoman Antonia Guichard just three months ago.

Russian President Vladimir Putin spoke to Rustam Minnikhanov on the phone, expressing his condolences to relatives and friends of the deceased, and to the Tatarstan leader personally.

Authorities and the airline's insurance company will pay compensation of around USD 93 700 to each of the victims' families. Monday was a day of mourning in Tatarstan.

Kazan is the capital of the oil-rich Russian Republic of Tatarstan, on the Volga River, about 720km (450 miles) east of Moscow.

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