Metrojet Flight 9268 crash sparks theories about mechanical failure, missiles and bombs

As the first bodies from theMetrojetFlight 9268wreckage arereturned to loved ones in Russia,investigators are left with the daunting task of figuring out how acommercial airlinersuddenlybrokeapart in mid-air, scattering pieces over Egypt'sSinai Province.

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Metrojet's Airbus A321-200 crashed Saturday23 minutes after taking off from the Egyptian Red Sea resort of Sharm el-Sheikh en route to St. Petersburg.Russian officials say it broke up at high altitude, killing all224 people on board.

The cause is unknown and Russianaviation authorities havecautioned people to"refrain from drawing conclusions" at this early stage of the investigation.

But already people have questionedwhether the plane was fit to fly, ISIS claims tohave shot it down with a missile,and military experts suggest a bomb may have been smuggled aboard.

Mechanical failure

Since the crash, a handful of people have come forwardto say the plane was in bad shape before it ever left the ground allegations the airline denies.

NatalyaTrukhacheva, identified as the wife of co-pilotSergeiTrukachev, said in an interview with Russian state-controlled NTV that her husband complained the "technical condition of the aircraft left much to be desired" before taking off on Saturday.

Another source atSharmel-Sheikh airport told Russian news agency RiaNovostithe plane hadexperienced "engine start failures several times over the past week," and thatcrew hadflagged these issues toairport technicians, according to the U.K.'s Independent newspaper.

The Globe and Mail reports the planehas had problems in the past, noting it was out of commission for several months in 2001 after theunderside of the rear fuselage slammed into the runway during a bad landing in Cairo.

The airline, however, has denied any suggestionsthe plane wasn't up to snuff.

"We rule out a technical fault of the plane or a pilot error," AlexanderSmirnov, deputy general director ofMetrojet, told a news conference Monday in Moscow. "The only possible explanation could be an external impact on the airplane."

Russian aviation agency'sAlexander Neradkodecried Metrojet's comments as "premature and not based on any real facts," but a number of experts have backed upSmirnov's claim that a mechanical failure is unlikely to cause a catastrophe on the scale of what happened toFlight 9268.

When planesbreak up in mid-air, experts say,it's usually because of one of three factors: aweather event, a collision or an external threatsuch as a bomb or a missile.

So far, it appears the skies were clear whenFlight 9268went down.

Shot down by an ISIS missile

Wilayat Sinai, alocal affiliate of the extremist groupISIS, claims itshot the plane down with a missile as retaliation forRussian airstrikes in Syria.

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Russianand Egyptian officials havedismissed the militants' claims as fabrications and a number of experts have dismissed the possibility a missile could reach the plane at 10 km above ground.

"They can put out whatever statements they want but there is no proof at this point that terrorists were responsible for this plane crash,"Mohamed Samir, anEgyptian army spokesman, told the Guardian newspaper. "The army sees no authenticity to the claims."

British military analyst Paul Beaver told The Associated Press that it's very unlikely ISIS possess amissile systemcapable of hitting a target at such a high altitude

"That's a very serious piece of equipment, and I don't think they have that sophistication," he said.

What's more, he added,theSinai desert is wellscrutinized by intelligence agencies, so a missile system would have been seen.

Bomb on board

The morelikely scenario,Beaver said, is that a bomb was on board.

Michael Clarke of theRoyal United Services Institute think-tank, agrees. He told the BBC that reports of the aircraft splitting in two suggesta "catastrophic failure, not a mechanical failure," which could mean an explosion on board.

"If we have to guess at this stage, it's much more likely to have been a bomb on board rather than a missile fired from the ground," he said.

Todd Curtis, a former safety engineer with Boeing, said investigators will be looking at more unusual events, such as an on-board fire or corrosion that caused a structural failure.

Too soon to speculate

Investigators, meanwhile, have not confirmed or denied any of these theories, cautioning people to be patient as the investigation is ongoing.

Neradko says it will bepossible to draw firm conclusions about the crash only after experts have studied the scattered fragments of the plane in Sinai and the content of its black boxes, which have been recovered and are in good condition.

Egyptian President Abdel-Fattah el-Sissi cautioned that the cause of the crash may not be known for months.

"It's very important that this issue is left alone and its causes are not speculated on," he told top government officials, including members of the military and security forces. The investigation "will take a long time" and "needs very advanced technologies."