Abstract: A Joint Combined Aircrew Systems Tester (JCAST) that can be used to test aircrew integrated life support equipment currently authorized for use by aircrew members of the Air Force, Navy and Army. The JCAST will be capable of Chemical/Biological seal testing of all the Joint Service Aircrew Mask (JSAM) variants including the Type 2 JSAM for high performance aircraft. Like traditional Testers, the JCAST is capable of Performance and Fit Testing of masks at pressure levels, including COMBAT EDGE (Combined Advanced Technology Enhanced Design “G” Ensemble), consistent with aircraft supply levels. The JCAST provides an apparatus and technique for accurately measuring a leak rate for an elastic body such as a chemical mask at 0.5 sccm at 6 IWG. The JCAST is portable and light weight while providing novel leak testing using pressure decay.