Overview Patented treated foam has a 98% efficiency rating. You replace only the low cost throw-a-way element. Easy, accurate servicing by replacement at specified times. Readily available to all F.B.O.'s distributed by most major aircraft supply houses. Dual stage foam element increases dust holding capacity It's a proven filter. Brackett Air Filters (formerly AC) have been in service on aircraft and helicopters since 1968. At present, Brackett Foam Filters are installed as Factory original equipment on 16 current production aircraft and four helicopters. Foam Filter is unaffected by water (approved for sea planes). It has no pleats to store dirt and is abrasive resistant. The cut-a-way shows the exclusive Brackett filter frame safety features.