The air test is recommended after stressing, cutting the tails, and installing the grout caps are completed. In other words, just prior to grouting. The purpose of air testing is to check for leaks, cross-overs between adjacent ducts, and other issues to allow repairs to be performed and/or grouting plans to be revised prior to grouting. This is the test referred to in the PTI Specification for Grouting of Post-tensioned Structures M55.1-19 Section 5.5.4.