Boeing mechanics caused $4 million of damage and could have sparked a mid-flight fire while repairing one of the planes in the Air Force One fleet, CNN reported quoting a federal investigation. 

The oxygen system aboard one of the two VC-25 aircraft available to President Donald Trump was contaminated while the plane was undergoing maintenance.

The mechanics “caused the mishap by supplying and using non-oxygen clean tools, parts, components, a regulator, and an unauthorized cleaning procedure while performing oxygen system leak checks,” according to the report.