Anti-Splat Aero (ASA), maker of after-market parts for experimental aircraft, has issued a service bulletin on their Air-Oil Separator system that many have installed in their aircraft. A recent forced landing of an RV-8 that blew out the crankcase seal due to over pressurization prompted the bulletin, although ASA maintains that most installations are problem free. The ASA system incorporates a vacuum valve that is tapped into the exhaust system to pull a suction on the crankcase breather line. On some aircraft, their exhaust tap is becoming clogged by coking oil residue. If it becomes sufficiently clogged, high crankcase pressure can result, and this can cause oil leakage or seal failure. They are recommending that all installations be inspected for coking at every oil change, and are offering a backup relief valve that can be installed to prevent cranks pressurization should the tap become clogged between inspections. The full text of their service bulletin (posted on the ASA web site) is below.
SERVICE BULLETIN 000-1
Date Effective: October 30, 2014
Subject: Vacuum Saddle Mount Evacuation System Maintenance
Required Action: Cleaning and Inspection of Bias Draw Tube
Time of Compliance: Before Further Flight and at Each Subsequent Oil Change
Level of Certification: Aircraft Owner
A potential problem has been brought to our attention with two recent incidents resulting in a forced landing of an RV-8 due to a clogged, coked breather. This occurrence and one other on an RV-10 that had a front seal blow out are the only ones we were made aware of (even one is too many). The models displaying serious coking potential have been the 10s and we suspended sales of the evacuation system to the 10s until we can be assured the problem no longer exists. We must add that several RV-10s have the system installed and are having no issues whatsoever. We are currently trying to sort out why, and what is different. When a good working solution is found we will make it available to all via our website and the forums. We addressed this at length on the forums as a safety precaution (it appears many were unaware and failed to receive this information). A.S.A. markets this product too many different experimental models and applications. We strongly advise everyone, with all aircraft models to inspect the tube where it protrudes into the exhaust immediately, and at every oil change to be certain it is open and free of any serious clogging. Many owners have carried out this inspection to find a small amount of coking, 1/16″ or so on the inside periphery is normal. This is not an issue and usually will not build further. We have also changed the design of the saddle mount clamp on to further help eliminate the potential problem. When we complete the testing program on this change we will report our results and make these available. We advise inspection at every oil change and if any significant build-up is detected, to inspect more often than that. If significant build-up is detected, then for safety a second valve to vent off crankcase pressure should be installed. We have the parts for this in stock should you need them. In light of recent developments, we will be offering the system complete with two valves and necessary hardware to install this bypass. We will also have a retrofit kit to add this safety feature on to existing installations. This forced landing would not have happened and it appears the root problem lies in the fact that we failed to get everyone adequately informed as to maintenance of this system.