Japan Airlines and All Nippon Airways have each found more than 100 cases in which their pilots skipped pre-flight alcohol tests.
The internal probe followed a series of incidences recently where Japanese airline pilots have been barred from flights due to alcohol-related issues.
All Nippon Airways said that during the year through November 2018, their pilots skipped breath tests in 393 cases.
Japan Airlines has found about 100 to 200 cases, in which its pilots skipped pre-flight breath tests.
Last month, the transport ministry inspected the offices of the 2 airlines, to investigate how they were enforcing their internal rules for pre-flight alcohol tests.