During a routine inspection of the dorsal fin airscoops, the technician discovered that material was missing from the air vanes (P/Ns 6512072-11 and 6512072-12) located in the transition duct (P/N 6512072-10-1).

The location and route of the missing material was a concern.

The material would have been routed into the ventilation J-box (air-mixing box) where it would have passed the cabin pressurization fresh air check valve and possibly wedge the valve open. With the valve open, the aircraft would not be able to hold pressurization.

The technician’s inspection revealed that a piece of the material was wedged in the check valve, and the valve could not seal.

Pieces of the material also passed through the overhead blower and wedged in the duct work. The blower cage was not damaged.

Part total time-3,545 hours.