Jeju Air jet still had a working engine when it crashed, investigation update says

The left engine sustained less damage than the right following a bird strike, but the left engine was shut down 19 seconds after the bird strike. 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.

Seoul: A Jeju Air plane that crashed in December during an emergency landing after a bird strike could have kept flying on the damaged engine that was still working after pilots shut down the other one, according to an update from South Korean investigators.

The Boeing 737-800 instead belly-landed at Muan airport 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 after the bird strike.

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.

More questions

So far, public attention has focused on the possibility that the crew may have shut down the less-damaged engine, rekindling memories of a 1989 Boeing 737-400 crash in Kegworth, England, where pilots shut down a non-damaged engine by mistake.

The disaster led to multiple changes in regulations including improvements in crew communication and emergency procedures.

A source told Reuters on Monday that 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 also raises the possibility that even the more heavily damaged engine that 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 to 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 (ARAIB) 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, said former US National Transportation Safety Board investigator Greg Feith when shown the document translated by Reuters.

It contains some new facts but omits far more, resulting in a "cryptic" document, he said.

ARAIB, which plans to issue a final report next 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 that 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 ARAIB. Safran did not immediately respond to a request for comment.

Jeju Air has previously said it is cooperating with ARAIB and is awaiting publication of the investigation.

Under global aviation rules, civil air investigations aim to discover crash causes without assigning blame or liability.

The Jeju Air pilots' union said ARAIB was "misleading the public" by suggesting there was no problem with the left engine given that bird remains were found in both.

A source who attended the briefing told Reuters that investigators told family members the left engine also experienced a disruptive "surge," citing black box data.

The pilot union and representatives of bereaved families have asked that evidence be released to support any findings.

Relatives say the investigation also needs to focus on the embankment containing navigation equipment, which safety experts have said likely contributed to the high death toll.

Global aviation standards call for any navigation equipment in line with runways to be installed on structures that easily give way in case of impact with an aircraft.

South Korea's transport ministry has identified seven domestic airports, including Muan, with structures made of concrete or steel, rather than materials that break apart on impact and has said it will improve them.

Designs for the new structures are in progress, a ministry official told Reuters last week.