NHK has learned that a group company of Japan Airlines failed to follow a mandatory maintenance procedure and allegedly deleted related records from its online system.

Transport ministry sources say that in September, a JAL Boeing 737 passenger jet took off from Tokyo's Haneda Airport for the southwestern prefecture of Kumamoto without a pre-flight maintenance check by a JAL Engineering official responsible for such work. Such checks are mandatory under the Civil Aeronautics Act.

The official noticed the failure soon after the plane's departure and reported it to a superintendent. The superior and others allowed the plane to continue flying.

They reportedly believed there would be no problem with having the plane undergo maintenance work after its fourth and last flight of the day.

It later became known that online records of relevant maintenance had been deleted and paper documents allegedly stashed in a personal locker.

JAL Engineering was also found to have repeatedly failed to use equipment as designated in a manual for checks conducted after changing of Boeing 767 wheel brakes.

In 39 out of 105 such checks by September, there were no records of the necessary equipment being taken out of a tool room. In 38 other cases, workers were found to have used equipment other than that designated.

Transport ministry officials say failure to conduct the checks properly is a serious rule violation that could result in accidents. The ministry plans to issue a business improvement advisory to JAL Engineering on Friday.