Upgrading the Apache means buying more "stuff". Seat tracks aren't very sexy but something you really need to work properly. So new(er) tracks are going in as we do other work. The seats are already out so it's another "while we are in there" upgrade. I got these from John Talmage of Diamondaire and he did a nice job of refurbishing them.
Not that I am aware of, but the FAA had defined "airworthy" The following is from the FAA certification site:
“ANSWER: There are two conditions that must be met for an aircraft to be considered "Airworthy”
1. The aircraft must conform to its type design (TC). Conformity to type design is considered attained when the aircraft configuration and the components installed are consistent with the drawings, specifications, and other data that are part of the TC, which includes any supplemental type certificate (STC) or other approved alterations.
2. The aircraft must be in a condition for safe operation. This refers to the condition of the aircraft relative to wear and deterioration, for example, skin corrosion, window de-lamination or crazing, fluid leaks, tire wear, etc.
If either of these two conditions cannot be met, the aircraft is considered to be un-airworthy.
So, the goal for those persons who operate and maintain aircraft is to keep them in an airworthy condition or what is referred to as “continued airworthiness”.
I may be able to help further if you tell me exactly what you're questioning.