Line training is on-job training

On-job training for pilots is called line training or simply LIFUS. It is the line flying under the supervision of more experienced pilot or instructor. The aim of line training is to teach the pilot to perform the flight according to the procedures approved for the operation of the particular aircraft type in a particular airline. Line training is therefore part of the mandatory training for which the aircraft operator is responsible - so-called operator conversion course. Simulated emergency situations are not practiced during line training. This is a training in how to perform the standard revenue flight. 

Line training is often referred to as line training, LIFUS, line flying under supervision, or supervision flying. Within the FAA the phrase supervised operational experience or SOE is commonly being used.

The aircraft operator is responsible for the scope and duration of the line training, its content, effectiveness and completion. Line training is completed by the line check.