Events Leading to This Priority Letter AD
This priority letter airworthiness directive (AD) is prompted by recent operator reports and the manufacturer’s report of several cracked filter housings on RAPCO, Inc. in-line pressure filters produced from lot numbers 05597, 07797, and 12597 and that have part numbers (P/N) RA-1J4-4, RA-1J4-6, and RA-1J4-7. The cracked filter housings are causing failure of the operators’ flight instruments during flight. This product is an in-line pressure filter used on single and twin-engine airplanes with pressure driven primary and standby flight instruments (attitude gyros). The filters are designed to remove the carbon particles between the vacuum pump outlet and the instrument pressure inlet. Failure of this filter results in failure of the flight instruments, which could cause loss of control of the airplane.
Further investigation has revealed that some of the plastic filter housings are cracking during flight when exposed to high temperatures and low humidity conditions. The failure is occurring anytime between 2 and 6 hours time-in-service (TIS). The manufacturer discovered that the vendor of the plastic made a manufacturing change, moving the sonic weld machine and the housings into a high humidity area. Apparently, the sonic weld time was doubled due to a higher moisture content in the plastic. This condition leads to brittle plastic filter housings that crack when exposed to low humidity/high temperature ambient conditions.
These filters may be installed on certain Cessna, Piper, and Raytheon airplanes.
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