This document specifies the procedures for testing flight stability of a multi-copter unmanned aircraft system (UAS) and is applicable to multi-copter type UAS that can take-off and land vertically. A commercial multi-copter UAS weighing over 250 g to less than 150 kg is discussed in this document. Further, this document is applicable to military and civilian multi-copter UAS. However, quantitatively specific stability criteria for the test are not specified in this document.