Test benches and Skydrol oil, but also airport equipment are typical Triple R applications.
In aviation applications are numerous.
First of all there is the famous SKYDROL aviation oil. Skydrol is a synthetic esther and specially designed to be explosion free.
Another application are the numerous Test benches. Test benches all use sophisticated but very sensitive servo-vales. They all require oil cleanliness levels of NAS 6 - ISO 18/16/14 or better.