This document provides guidance for oxygen cylinder installation on commercial aircraft based on rules and methods practiced in aerospace industry and applicable in other associations.It covers considerations for oxygen systems from beginning of project phase up to production, maintenance, and servicing.The document is focused on requirements regarding DOT approved oxygen cylinders. However, its basic rules may also be applicable to new development pertaining to use of such equipment in an oxygen environment.For information regarding oxygen cylinders itself, reference should be made to AIR825/12 also. ARP5021A has been reaffirmed to comply with the SAE five-year review policy.