What was found
(CAN) DURING AN 100 HR INSPECTION, THE AIR FILTER WAS BEING REPLACED. THE FILTER WAS FOUND DAMAGED AND REPLACED. INVESTIGATION REVEALED NO APPARENT REASON. THE PILOT WAS ASKED IF A BACKFIRE CONDITION OCCURRED AND NONE WAS EXPERIENCED AT THE TIME. THIS IS THE FIRST THAT’S BEEN SEEN OF THIS AND ONLY ASSUME AT THIS TIME. HAVE SENT PICTURES TO ROBINSON HELICOPTERS TO GET SOME FEED BACK. ASSUME IT WAS DUE TO A CARB FIRE AND THE HEAT DISTORTED THE FILTER.