The FAA letter defining “Preventive Maintenance” is located here.
The letter is an FAA interpretation of what may (or may not) constitute “Preventive maintenance” under FAR 43.3 and Part 43 Appendix A as applied to Part 91 operations.
The letter extends the definition of “preventive maintenance” to include items/tasks that are similar to something that is listed in Appendix A, but may not be specifically called out.
Further discussion is available on AOPA’s site here:
https://www.aopa.org/news-and-media/all-news/2019/october/pilot/savvy-aviator-preventive-maintenance
