Assumption + Miscommunication = Aircraft Damage

In a recent event on the flight line, maintenance personnel were prepping an aircraft for an engine run. The jet engine mechanic performed the Inlet and Exhaust (I&E) inspection on the number one engine. He purposefully left the inlet mat in the inlet so the oncoming 7-level trainer could train a 3-level on conducting the I&E inspection. After completing the training, the trainer also purposefully left the inlet mat in the inlet, assuming the engine mechanic would go back and re-accomplish the intake inspection. The engine mechanic trusted the experience of the trainer, however, and chose not to re-accomplish the inspection prior to the engine run but did not communicate this decision to the trainer. Also, the trainer did not communicate to the engine mechanic that the mat was still in the inlet. For the engine run to take place, an engine run supervisor was needed. The supervisor conducted a “walk-around†inspection, made sure the chocks were in place, and ensured nothing was below or around the engines. During the engine run, the engine mechanic and the supervisor did not notice anything out of the ordinary, and there were no abnormal engine indications from the flight deck. Once the operational check was complete, they shut the engines down. When the engine run supervisor performed the post-engine run I&E inspection, he discovered remains of the inlet mat in the exhaust and damage to the number one engine. During aircraft maintenance, do not assume anything and question everything.