The footage shows a jet barreling down a runway in South Korea at high speed before it hits a barrier and catches fire, killing 179 of the 181 people aboard. To experts in crash investigations, the video raises more questions than it answers.

Why hadn’t the landing gear deployed? Were any systems malfunctioning?

The cause of the crash probably won’t be determined for months, following a rigorous investigation. And experts said investigators are expected to focus on a wide range of issues, including what the pilots were doing and saying, why the processes and mechanisms typical of an airplane landing failed, the weather conditions and whether the airplane had received proper maintenance by the airline.

“This one is very much an open-book mystery at this point,” said Shawn Pruchnicki, an aviation safety expert and professor at Ohio State University.

Plane crash experts warned against drawing conclusions about the cause until further review of the evidence. The information circulated in the days after such incidents is often scant or even incorrect, they said. Theories developed early on are often later disproved. And crashes typically have multiple causes, some of which may not be immediately apparent.

“The aviation industry is built on redundancy and there are very few single-point failures in airplane design or airplane operations,” said Jeff Guzzetti, a former accident investigator for the Federal Aviation Administration and National Transportation Safety Board, which investigates plane crashes. “Typically, it’s a combination of factors.”

Officials in South Korea said they had recovered the plane’s black boxes, which contain troves of data and recordings that will be vital to understanding what went wrong. That and other evidence from the wreckage should shed more light on what the pilots were doing and saying leading up to the crash and whether any systems were malfunctioning, experts said.

When a plane’s wheels are not deployed during a landing, as was the case in the crash on Sunday, pilots should receive warnings alerting them to that fact, experts said. The plane involved in the crash, a Boeing 737-800, is also equipped with a backup system that allows the pilots to manually release the landing gear, if needed. But the pilots may have had other things on their mind, said John Cox, the founder of Safety Operating Systems, an aviation safety firm.

“What’s the most pressing issue? If it is controlling the jet, then everything else takes a back seat,” he said.

Footage of the crash also raised other questions. A reverse thruster, used to slow the plane on landing, appeared to be in use on only one engine, which is unusual, Pruchnicki said. The flaps and slats on the plane’s wings, which are also used to slow it down during landing, did not appear to be extended either, according to the experts.

Landing gear is vital, but planes have safely landed with malfunctioning gear. Had the plane in Sunday’s crash not hit a barrier at the end of the runway, it’s possible the death toll may not have been so high, experts said.

In addition to looking into why the landing gear was not deployed, officials in South Korea are also investigating whether one or more birds struck the jet, contributing to the crash. Such bird strikes are not uncommon in aviation, but typically do not result in such catastrophes.

If one engine had been damaged, the plane should have been able to land with the other. But had both engines stopped functioning, the pilots would have been frantically trying to land the plane safely, Cox said. It is also possible that the pilots were trying to abort the landing, which could explain the speed with which the plane was moving and why certain landing mechanisms did not appear to be in use, according to Guzzetti.

Other factors could be at play, too, including insufficient or faulty maintenance of the plane. The jet in the crash was 15 years old, which is not unusual for a passenger plane, and should have undergone routine maintenance by the airline, including “heavy checks” in which the flooring is removed and the plane undergoes comprehensive inspections and maintenance. Investigators are expected to review the records of such work.

While there are several possible causes of the crash, experts said that there was little reason to believe that the plane’s design was among them. The 737-800 was a bestselling jet for Boeing for years because it is well-suited to a wide range of flight routes and allows airlines to economically carry many passengers — from about 160 to 190, depending on seating configurations. It also has a stellar safety record, experts said. The plane has been flying for more than 25 years, with thousands now in circulation, accounting for about 1 in 7 passenger planes in service around the world, according to Cirium, an aviation data firm.

This article originally appeared in The New York Times.

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