input: [Number] 25-20 [Office] ANM-111 [Date] 09-10-1996 [Title] 
output: Pressurization, Ventilation and Oxygen Systems Assessment for Subsonic Flight including High Altitude Operation Provides guidance on methods of compliance with the requirements of part 25 of the Federal Aviation Regulations pertaining to pressurization, ventilation, and oxygen systems, especially as they pertain to high altitude subsonic flight. As with all AC material, it is not mandatory and does not constitute a regulation. The applicant may elect to follow alternate methods provided that these methods are also found by the FAA to be an acceptable means of complying with the requirements of part 25. Because the guidance on the methods of compliance presented in this AC are not mandatory, the terms "shall" and "must" when used herein, apply only to an applicant that chooses to follow a particular method without deviation.