This SAE Aerospace Information Report (AIR) provides information on anti blow-by design practice for cap-strip seals. Suggestions for piston cap strip seal sidewall notch design and other anti blow-by design details are also described. It also includes information on two key investigations based on the XC-142 as part of the text and as Appendix A. The purpose of this document is to provide adequate information to the designer so that the problem will not reoccur.