KAZAN, Russia (AP) — The grainy airport video is dark, short and chilling. Within five seconds, a dot of light that Russian authorities say is a Boeing 737 appears in the sky over the tarmac and plunges to the ground in a near-vertical crash. The result is a blinding fireball.
The video shown Monday by Russian television stations of Sunday's horrifying crash at Kazan airport that killed all 50 people onboard raises a host of questions, including why the plane's second attempt to land at night in good weather went so horribly wrong.
Experts from the NTSB, Boeing and the FAA were heading to the scene to help Russian investigators, who were combing through the incinerated wreckage on Monday after fire crews spent hours extinguishing the blaze.
The Boeing 737 plane belonging to Tatarstan Airlines crashed Sunday night at its home port of Kazan, 720 kilometers (520 miles) east of Moscow.
It was making its second attempt at a landing, according to Alexander Poltinin, head of the local branch of Russia's Investigative Committee, who said investigators were looking into possible pilot error or equipment failure.
Poltinin said it could take weeks to identify the remains.
The traffic controller at the Kazan airport who contacted the plane before the crash said the crew told him they weren't ready to land as it was approaching but didn't specify the problem.
The brief video taken by an airport security camera showed the plane going down at high speed at a nearly vertical angle and then hitting the ground and exploding. It was confirmed as authentic to The Associated Press by the emergency press service at Kazan airport and other Russian officials.
The investigators have found both of the plane's black boxes but said they were damaged. The boxes — which record the plane's performance and the crew's conversations — are essential for the crash probe.
Magomed Tolboyev, a highly decorated Russian test pilot, said on Rossiya television that it wasn't immediately clear why the crew was unable to land on their first try in good weather.
U.S. National Transportation Safety Board spokesman Eric Weiss said Monday that a team of eight U.S. aviation safety experts were heading to Russia to assist: three NTSB crash investigators, a U.S. Federal Aviation Administration investigator and four experts from the plane manufacturer.
John Cox, an aviation safety consultant who flew 737s for 15 years for US Airways, said one of the first issues investigators will look at based on the nearly vertical angle of descent in the video will be whether the plane experienced an aerodynamic stall, which usually occurs when a plane slows to the point where its wings lose lift.
"Anytime you have an airplane that gets this vertical, the immediate suspicion is that it stalled," Cox said in an interview.
Investigators on Monday started looking through the company's records, which showed the plane was built 23 years ago and had been used by seven other carriers prior to being picked up by Tatarstan Airlines in 2008.
In 2001, it was damaged in a landing accident in Brazil that injured no one.
The company insisted that the aircraft was in good condition for the flight.
The carrier has had a good safety record but appears to have run into financial problems recently. Its personnel went on strike in September over back wages, and the Kazan airport authority has gone to arbitration to claim what it said was Tatarstan Airlines' debt for servicing its planes.
Industry experts have blamed some recent Russian plane crashes on a cost-cutting mentality at some carriers that neglects safety in the chase for profits. Insufficient pilot training and lax government controls over the industry also have been cited as factors affecting Russian flight safety.
Former Finance Minister Alexei Kudrin said Monday that the government should tighten its oversight of carriers and subsidize the upgrading of their fleets to improve safety.
Russia's last deadly airliner crash was in December, when a Russian-made Tupolev belonging to Red Wings airline careered off the runway at Moscow's Vnukovo airport. It rolled across a snowy field and slammed into the slope of a highway, killing five of its eight crew members.
A 2011 crash in Yaroslavl killed 44 people including a professional hockey team and was blamed on pilot error.
Isachenkov reported from Moscow; Transportation Reporter Joan Lowy in Washington, DC, contributed to this report.