One of the pilots of Asiana Flight 214 that crashed in San Francisco shouted warnings that were ignored, according to South Korean media.
Sources in the country's transport ministry confirmed Bong Dong Won - who was in the cockpit jump seat - repeatedly yelled "sink rate" in the final minute before the crash, it was reported.
If the sink rate - the rate of decrease in altitude - was checked when Mr Bong raised the alarm, it may have prevented the plane from hitting the seawall as it landed at San Francisco Airport, reports said.
But the two pilots at the controls - Lee Kang Kuk and his instructor Lee Jung Min - apparently did not respond to Mr Bong's shouted warnings, the respected Joongang Daily newspaper said.
The crash killed two Chinese students and left more than 180 injured.
Among those injured were three flight attendants in the back of the plane who survived despite being thrown onto the runway as the plane crashed on Saturday.
US investigators previously said that just 1.5 seconds before the plane crashed, a member of the flight crew asked to abort the landing, though it was too late to take such action.
However, it is now being reported that Mr Bong started giving warnings 54 seconds before impact.
There was also a fourth pilot - the relief captain - on board, but he was not in the cockpit at the time of the crash.
The US National Transportation Safety Board (NTSB) has confirmed that Mr Bong had flown five to six times to San Francisco and previously worked for the Korean air force as a fighter pilot.
Lee Kang Kuk was around halfway through his training for the Boeing 777, but had led 29 flights to San Francisco on Boeing 747s in the past, according to the airline.
However, his trainer had not flown in that role before , the NTSB said.
At 41, Mr Bong is much younger than the other two pilots in the cockpit.
A Korean Airlines Boeing 747 crashed in Guam in 1997 - a crash that investigators blamed in part on an authoritarian cockpit culture that made newer pilots reluctant to challenge captains.
But since then, the industry has adopted broad training and requirements that mean pilots who are not at the controls should feel free to voice any safety concerns.
Sky News producer Jen Kwon, a South Korean based in Beijing, said: "Even though Bong Dong Won is younger than the other two pilots in the cockpit I do not believe that age or rank would be a reason why people would not respond to a warning.
"Perhaps conservative Korean traditional culture might be a bar to communication in many aspects of Korean life, it is hard to imagine the same happening in a cockpit of a civil airliner after seeing what had happened to their competing airline company, Korean Airlines."
South Korean-based Asiana has defended the four pilots as "very competent".
The airline's chief executive, Yoon Young-Doo, lashed out at reports that pilot inexperience may have been to blame for the fatal crash, saying such speculation was "intolerable".
The aircraft went skidding out of control after clipping the seawall, breaking up and bursting into flames when one of its engines caught fire.
The NTSB said the plane was flying far too slowly before the landing. Its investigation is expected to continue for months and it has warned against speculating about the cause of the crash.
But the Air Line Pilots Association International (Alpa) has already criticised the information provided by the NTSB.
"The NTSB's release of incomplete, out-of-context information has fuelled rampant speculation about the cause of the accident," Alpa said.