Russian Plane's Mid-Air Breakup a Puzzle in Modern Jet Era

Investigators examining the crash of a Russian passenger jet in the Egyptian desert have an advantage over recent high-profile probes - with the impact zone readily accessible, the debris field unencumbered by jungle or water and plane's flight recorders already located.

With wreckage spread over a wide area, there's also little doubt that the plane broke up in the sky. Reading the recorders, known as black boxes, should help with the complex task of explaining how an airliner built to withstand extreme turbulence and equipped with computerized flight limits to ensure it maintains control could have been ripped to pieces.

"They've got the wreckage, they've got the recorders, they've got the air-traffic-control recordings," said Paul Hayes, safety director at London-based aviation consultancy Ascend Worldwide. "Assuming the recorders are in good condition they should have initial views within a week."

The Metrojet Airbus Group A321 plummeted into a remote area of Egypt's Sinai peninsula 23 minutes after leaving the Red Sea resort of Sharm el-Sheikh on a flight to St. Petersburg, killing all 224 people aboard. Wreckage was found in an area about 8 kilometers long and 4 kilometers wide 5 miles long by 2.5 miles wide, suggesting the aircraft broke up at high altitude, Alexander Neradko, the head of the Russian Federal Aviation Authority, said in an interview with Rossiya-24 state television.

The easily accessible wreckage and the intact recorders should help investigators compared to more difficult crashes. After Air France Flight 447 disappeared over the Atlantic Ocean en route from Rio De Janeiro to Paris in 2009, the search for the recorders took two years.

In the case of Malaysia Air Flight 370, which went missing two years ago, the wreckage itself has yet to be located, except for a small piece from the wing that washed up on shore this summer. For the crash of Flight 17 over Ukraine, the probe was hindered by political conflict that limited access to the site of the wreckage and possibly contributed to evidence being tampered with.

To find out what happened, investigators of the Metrojet crash will start with listening to the cockpit voice recorder. The more complex task is synchronizing those recordings with information from the flight data recorder to piece together what happened to the plane. Egyptian authorities have said they have the equipment required to do that decoding.

If the airplane did indeed break up at high altitude, investigators will be looking at causes of similar crashes such as bombs, missiles, on-board explosions and structural failures.

"It's very hard to pull one of these things apart in flight. Very hard," said John Cox, a former U.S. airline pilot who has participated in accident investigations.

While the Islamic State's Sinai affiliate claimed responsibility for shooting the plane down, Egyptian and Russian officials said those claims weren't credible. Only the most sophisticated ground-based missiles can reach 31,000 feet (9,450 meters), the cruising altitude at which the Metrojet encountered problems and began to fall.

That doesn't rule out a bomb like the one that detonated aboard Pan Am Flight 103 as it was carrying holiday travelers from London to New York on Dec. 21, 1988. A small explosive device smuggled aboard in checked luggage blew out the side of the Boeing 747 and it came apart over Scotland, according to Britain's Air Accidents Investigation Branch report.

So far, neither Egyptian nor Russian officials have said there's any evidence of a bomb. Explosive devices cause telltale pitting on nearby metal and also leave chemical residue, according to the U.S. National Transportation Safety Board, so an examination of the wreckage should tell investigators whether or not that was the cause.

One area investigators will pay close attention is damage to the Metrojet A321 when its tail struck the runway while landing in Cairo in 2001. The plane was repaired and returned to service, according to Ascend Worldwide Ltd., a London-based company that gathers data for insurers.

There have been at least two similar accidents caused by improper repairs after tail damage.

China Airlines Flight 611, a Boeing 747 flying from Taiwan to Hong Kong on May 25, 2002, broke apart when a repair failed, causing an explosive decompression, according to Taiwan's Aviation Safety Counsel. All 225 people aboard died when it fell into the Taiwan Strait. The jet's tail had been repaired 22 years earlier, according to the investigation.

Japan Airlines Flight 123 crashed into a mountain in Japan on Aug. 12, 1985, after a repair to its tail came apart, destroying key flight control surfaces. Seven years earlier, its tail had been repaired after striking the ground during touchdown, according to Japan's Aircraft Accident Investigation Commission. The crash killed 520 out of 524 people on board.

In both cases, part of the structure that holds in air at high altitudes, known as the aft pressure bulkhead, was damaged when the planes' tails scraped the runway. Some photos of the wreckage in Egypt appear to show that the plane's tail section fell separately from the rest of the plane. The Russian airline rejected the idea that tail repairs could have caused the crash, saying also that the plane had been properly maintained.

Another cause of midair breakups has been explosions in aircraft fuel tanks, according to Steve Wallace, former chief of the U.S. Federal Aviation Administration's accident investigation division. TWA Flight 800, another 747, crashed into the Atlantic Ocean near New York on July 17, 1996, as a result of such an explosion, killing all 230 aboard, according to the NTSB.

"Unless there's something that says 'obvious,' you generally have to wait until you get the reports from the recorders," said Robert Mann, a former American Airlines executive who is president of R.W. Mann & Co. and an aviation consultant, said in an interview.

© 2015 Bloomberg L.P.