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.
This from Sky News
It's all coming out in the wash.