The clues emerging so far about the final moments of Metrojet Flight 9268 don’t paint a clear picture of what happened to the doomed passenger jet.
Was a midair heat flash that a U.S. satellite detected over the Sinai Peninsula when the flight went down a sign of an explosion aboard the plane?
And if that was the case, why haven’t investigators found signs of an explosive impact on the crash victims’ bodies, as Russian state media reports?
There are a wide range of theories on what made the passenger jet plunge to the ground, killing all 224 people on board, but Russian officials say it’s too soon to speculate on the cause.
Aviation experts agree, and officials have downplayed an apparent claim by Islamic militants that they brought down the Airbus A321-200, saying technical failure is the most likely reason for the crash.
Here’s the latest on what we know:
Flight 9268 was on its way from the Egyptian resort of Sharm el-Sheikh to St. Petersburg early Saturday when it dropped off radar about 23 minutes into the flight, Egyptian officials say.
Air traffic controllers apparently didn’t receive any distress calls.
Russia’s privately owned Interfax news agency quoted an unnamed source in Cairo as saying the plane’s cockpit voice recorder (CVR) had captured uncharacteristic sounds the moment before the flight disappeared.
It cited the source as saying that an “unexpected’ and “nonstandard (emergency)” occurred “instantly,” which was why the pilots failed to send an emergency or alarm signal.
The website Flightradar24, which tracks aircraft around the world, said it had received data from the Russian plane suggesting sharp changes in altitude and a dramatic decrease in ground speed before the signal was lost.
Intelligence analysis has ruled out that the Russian commercial airplane was struck by a missile, but the satellite data suggests that there was a catastrophic in-flight event — including possibly a bomb, though experts are considering other explanations, according to U.S. officials.
Analysts say heat flashes could be tied to a range of possibilities, including a bomb blast, a malfunctioning engine exploding or a structural problem causing a fire on the plane.
A top Russian aviation official has said the plane broke apart in midair.
Metrojet official Alexander Smirnov said the airline had ruled out technical problems and human error. Protection systems on the plane would have prevented it from crashing, he said, even if there were major errors in the pilot’s control equipment.
CNN aviation analyst Peter Goelz said the disaster could have resulted from “some sort of catastrophic failure, perhaps caused by an earlier maintenance problem. It could have been a center fuel tank that might have exploded.”
But on the bodies of victims recovered so far, investigators haven’t found any sign of explosive impact, Russian state media reported Tuesday, citing unnamed sources.
Russia’s state-run TASS news agency reported that Russian and Egyptian experts had not found any blast-related trauma during their preliminary examination of the bodies, citing a Russian source within the investigation.
Explosives expert Chris Owen, from Alford Technologies, told CNN that if swabs had been taken from plane debris quickly — while the wreckage was dry — it could be possible to identify any explosive residue in a lab.
“However, there would probably be quicker and more obvious evidence from the type of damage sustained by bits and pieces around the bomb,” he said. “Surfaces in the vicinity of any explosion would be expected to be bent, perforated, petaled, spalled, sheared, frayed, charred (especially fibers), melded by impact, and otherwise characteristically damaged.”
Owen said it would be hard to rule out a bomb blast just because evidence of one had not been discovered. “If a bomb is ruled out, it will likely be because another cause has been found,” he said.
The A321-200 was built in 1997, and the airline company Kogalymavia, which flies under the name Metrojet, had been operating it since 2012, Airbus said. The aircraft had clocked around 56,000 flight hours over the course of nearly 21,000 flights, the plane maker said.
So far, officials have said all its inspections were in order.
The aircraft passed a routine inspection before takeoff, Egyptian Airports Co. chief Adel Al-Mahjoob said Saturday.
According to the Aviation Safety Network, which tracks aircraft incidents, the same plane’s tail struck a runway while landing in Cairo in 2001 and required repair. At the time, the aircraft was registered to the Lebanese carrier Middle East Airlines, registration records show.
Kogalymavia’s Andrei Averyanov said the plane had been damaged in 2001, but had most recently been thoroughly checked for cracks in 2013. Not enough time had passed for major cracks to develop to a critical size since then, he said.
Smirnov, the Metrojet official, said that he had personally flown the plane in recent months and that it was “pristine.”
There were 217 passengers and seven crew members on board Flight 9268. Of the passengers, 209 were Russian, four were Ukrainian and one was Belarusian. The citizenships of three other passengers are unknown.
Russian media reported that the disaster created a large number of orphans in Russia, as a lot of parents left their young children with relatives while they took vacations in Sharm el-Sheikh.
Most of the bodies retrieved at the crash site are intact, a medical source in Sinai told CNN on Monday, and showed no major burns.
A spokeswoman from Russia’s Ministry of Emergency Situations told CNN Tuesday that 19 victims had been identified.
“The identification of the bodies is going on even now into the evening because of so many victims,” she said. “We will continue the identification process tomorrow morning as well.”
Egyptian President Abdel Fattah el-Sisi has promised Russian President Vladimir Putin that he will allow “the broadest possible participation of Russian experts in the investigation,” according to the Kremlin.
Russian officials have joined their Egyptian counterparts at the crash scene. Putin has also ordered a Russian investigation, the Kremlin said.
Aviation investigators from France and Germany, the countries where the plane was manufactured, are also taking part.
The aircraft’s engines were manufactured in the United States. If the plane’s engines become a focus of the investigation, the U.S. National Transportation Safety Board will likely dispatch a team to Egypt as well, a U.S official with knowledge of the investigation said.
Egypt has begun to analyze data off the plane’s flight data recorders known as “black boxes,” Egypt’s Civil Aviation Ministry announced Tuesday. Experts started retrieving data from the recorders on Monday, the ministry said.
The French Aviation Authority said Tuesday it had investigators helping with the data analysis as well as at the crash scene. Airbus engineers were also in Egypt working on the investigation, it said.
Sharm el-Sheikh, where Flight 9268 began its journey, is a beach resort dotted with palm trees at the southern tip of Sinai. The plane crashed about 300 kilometers (185 miles) farther north, near a town called Housna, according to Egyptian authorities.
Sinai has been a battleground between ISIS-affiliated militants and Egyptian security forces in recent years. Hundreds have died in the fighting.
The militants appeared to claim responsibility for bringing down the Russian passenger jet in a statement posted online Saturday, but officials in Egypt and Russia disputed it.
Mahjoob, the airport official, said there was no evidence of a terrorist attack. And Russian Transport Minister Maxim Sokolov said the claim that terrorists brought down the plane with an anti-aircraft missile “cannot be considered reliable,” according to RIA Novosti.
Metrojet executives also said Monday that it was too early in the investigation to speculate or draw any conclusions. But Smirnov referred to purported footage of the crash posted by militants, saying: “Those images you have seen on the Internet; I think they are fake.”