Preliminary results of an investigation into Sunday’s fatal airplane crash in Kazan have found that pilot error and technical factors, including equipment failure, were major causes of the disaster.

According to investigators, the Tartarstan Airlines Boeing-737-500 fell almost vertically between the runway and the taxiway. The explosion of fuel tanks caught fire, which could only be completely extinguished in the morning. Fire centers reignited at night, according to Alexander Poltinin, the head of the Volga Department of Transport Investigation Committee (IC).

Poltinin noted that for some strange reason, the crew took the plane on a second round. The investigation committee is now searching for answers about why the pilots could not land the liner at the first attempt.

That plane’s crew was trying to get in touch with ground services before landing, Poltinin told RIA Novosti.

It was reported earlier that the dispatchers, who were directing the plane to a landing, have already been questioned. Kirill Kornishin, an air traffic controller, told the Russia 24 TV channel that one of the pilots reported that the plane is going into the second round before landing.

“He said that the configuration was not favorable for landing. I gave him a set like it should be normally. He confirmed and did not go away. It literally happened in a few seconds," Kornishin said. All 50 passengers died in the crash.

In the Moscow airport where the plane took off, investigators have taken samples of fuel and lubricants. Tatarstan Airline seized all the documents on the technical condition of aircraft and pilot flight training, Poltinin said.

The bodies of all passengers have been found. On board were some well-known Russian names, inlcuding Irek Minnihanov, the son of the president of the Republic of Tatarstan, and the republic’s head of the Federal Security Service, Alexander Antonov. Two foreign passengers, a British citizen, Donna Carolina Bull, and Margarita Oshurkova from Ukraine, were also on the flight.

Investigators are now examining the plane’s black boxes, which were found in the morning in the crater formed after the crash. While they have not been deciphered yet, the experts are making pretty conservative assumptions about the causes of the accident.

A source in the operational headquarters for emergency management told Interfax that he does not rule out "problems with the mechanization of the wing, also the engines possibly could not have enough traction when trying to go on the second round."

However, the first deputy chairman of the Duma Committee on Transport, Michael Bryachak, considers a technical fault to be the least likely cause of the disaster.

Several aviation experts suggested that Russian pilots flying for small, regional airlines are not trained to fly the Boeings, having been trained to fly Russian planes such as the Tupolev.

According to the deputy chairman of the Duma Committee on Transport, Alexander Starovojtov, "the pilot did not have the qualifications to start landing."

Oleg Beliy, the head of the Institute of Transportation Problems of RAS, agreed and explained that modern airlines refused to use the domestic aircrafts, because they had bad noise characteristics and could not be used for flights abroad.

"Pilots continue to be taught on the old domestic simulators. Airlines do not train their professionals, they are willing to take ones who learned to fly the Russian [Tupolev] rather than Boeings," Beliy said.

Oleg Smirnov, a pilot and the chairman of the Civil Aviation Transport Supervision of the Public Council of Rostransnadzor, said pilot inexperience flying Boeings could not be ruled out, but the main reasons for the accident were a large number of preconditions for flight accidents.

"In 2011, we became leaders in the number of plane crashes. In 2012 it got better, and in 2013 we have already had two disasters,” he said. “The fact is that we have a very bad system of regulation of civil aviation. Flight certificates are issued, and accidents are investigated by the same people.”

Smirnov said that as an example, in the United States a separate structure is engaged in investigating, the head of which is appointed by the president, “and no airline can respond to its regulations."

According to Smirnov, in most cases in Russia, pilots who are killed are found guilty, and addressing systemic problems is delayed.

"Neither we nor any other state agency is responsible for flight safety. The expert community is talking about it, no one argues with us, but neither do they solve the situation," he said.