The Boeing 737-800 instead belly-landed at Muan airport in December without its landing gear down, overshot the runway and erupted into a fireball after slamming into an embankment, killing all but two of the 181 people on board.
Investigators have not yet produced a final report into the deadliest air disaster on South Korean soil, but information about the plane's two engines has begun to emerge.
According to a July 19 update prepared by investigators and seen by Reuters but not publicly released following complaints from victims' family members, the left engine sustained less damage than the right following a bird strike, but the left engine was shut down 19 seconds afterwards.
The right engine experienced a "surge" and emitted flames and black smoke, but investigators said it "was confirmed to be generating output sufficient for flight" in the five-page update, which included post-crash photos of both engines.
No reason for the crew's actions was given and the probe is expected to last months as investigators reconstruct the plane's technical state and the picture understood by its pilots.
Experts say most air accidents are caused by multiple factors and caution against putting too much weight on incomplete evidence.
A source told Reuters on Monday the South Korea-led probe had "clear evidence" that pilots had shut off the less-damaged left engine after the bird strike, citing the cockpit voice recorder, computer data and a switch found in the wreckage.
But the latest update on the crash raises the possibility the more heavily damaged engine, which was still running, could have kept the plane aloft for longer.
It did not say what level of performance the operating engine still had, nor what extra options that might have given the plane's emergency-focused crew before the jet doubled back and landed in the opposite direction of the runway from its initial plan, with its landing gear up.
Both engines contained bird strike damage and both experienced engine vibrations after the strike.
The right engine showed significant internal damage, the Korean-language update from South Korea's Aviation and Railway Accident Investigation Board said, but it did not describe the damage found in the left engine.
The update did not say how the left engine was operating, nor the state of systems connected to either engine, former US National Transportation Safety Board investigator Greg Feith said when shown the document translated by Reuters.
It contained some new facts but omitted more, resulting in a "cryptic" document, he said.
The South Korean board, which plans to issue a final report in June, did not immediately respond to a request for comment.
Safety experts say it is common for early reports to contain sparse facts and limited analysis while investigations continue.
A preliminary report released in January said feathers and blood stains from ducks were found in both engines.
The engines - made by CFM International, jointly owned by GE and France's Safran - were examined in May and no defects or fault data were found beyond the bird and crash damage, the report said.
Families of those who died in the disaster were briefed on the engine findings but asked investigators not to release the July 19 report, saying it appeared to apportion blame to the pilots without exploring other factors.
The report was withheld but Reuters and South Korean media obtained copies.
Boeing and GE referred questions about the crash to the South Korean board.
Safran did not immediately respond to a request for comment.
Under global aviation rules, civil air investigations aim to discover crash causes without assigning blame or liability.
