Investigators have found both of the flight recorders, or "black boxes".The Boeing 737 was arriving from Moscow and trying to land, but exploded on impact at about 19:20 local time (15:20 GMT) on Sunday, officials said.The Tatarstan Airlines jet had 44 passengers and six crew on board.A British teacher, Donna Bull, was among those killed. The 53-year-old from Bellersby College in Cambridge was travelling with a Moscow-based colleague, Yana Baranova, who also died.Investigators are now looking at whether a technical failure or crew error may have caused the crash.Russia's Lenta.ru news website says an act of terrorism has been ruled out.Transport Minister Maxim Sokolov said "the plane was vertical, practically vertical, but the [video] recordings aren't very high-quality because it was dark".Investigative committee official Vladimir Markin told Rossiya 24 TV that experts were checking whether poor-quality fuel and weather conditions could have been contributing factors.It was raining in Kazan when the aircraft crashed. The city is by the Volga River, about 720km (450 miles) east of Moscow. Debris and bodies are scattered over a wide area and officials will start collecting DNA from relatives on Monday to help with the identification of victims, Russian media report.Among the dead was Irek Minnikhanov, a son of the president of the Russian Republic of Tatarstan, according to the official passenger list.Aleksander Antonov, who headed Tatarstan's branch of the Federal Security Service, was also among the passengers.The victims also included two children.Russian President Vladimir Putin "expressed his condolences to the relatives of the victims in this horrible disaster", his spokesman Dmitry Peskov was quoted by the news agency Interfax as saying.A government commission has been set up to investigate the cause, he said.Reports said the pilot, 47-year-old Rustem Salikhov, had already tried to land several times before crashing.The crew had said they were not ready to land because of technical problems, Russian news agencies report.A journalist who said she had flown on the same aircraft from Kazan to Moscow earlier on Sunday told Russia's Channel TV that there was a strong vibration during the landing in the Russian capital."When we were landing it was not clear whether there was a strong wind, although in Moscow the weather was fine, or some kind of technical trouble or problem with the flight," said Lenara Kashafutdinova."We were blown in different directions, the plane was tossed around. The man sitting next to me was white as a sheet."The plane had been in service since 1990, Russian officials are quoted as saying by the local media.The airport in Kazan - the capital of Tatarstan - has been closed since the accident and is not expected to re-open until Monday afternoon.Family members and friends of the victims are getting help by a team of psychologists. The government also promised financial compensation.The BBC's Daniel Sandford in Moscow says that although some of Russia's biggest airlines now have very good reputations, frequent crashes by smaller operators mean the country has one of the worst air safety records in the world.ANN.Az