Standard 161 defines the requirements for air quality in air-carrier aircraft and specifies methods for measurement and testing in order to establish compliance with the standard.The revised 2018 edition of the standard incorporates a number of changes to the 2013 edition. Notably, the document includes a new Section 10 with a standardized reporting form to assist maintenance workers in their troubleshooting process. The new edition also provides additional guidance related to maintenance protocol for checking and adding oil to APUs.