Small mistakes can sometimes have big consequences. That’s the lesson one maintenance team is likely taking away from a recent mishap that caused millions in damages to an F-35, a U.S. military fighter jet that costs about $110 million to manufacture.

According to an aircraft accident investigation report released by the U.S. Air Force, a handheld flashlight left in the engine of an F-35 caused nearly $4 million in damage and created a situation that could not be repaired locally.