During the working schedule, the work center may have Availability Loss - any time work isn't being done on the work order - due to breakdowns, shortages in raw materials, prep time, cleanup time.
During the working schedule, the work center may have Performance loss - any time work is slower than the full capacity of the work center - due to poorly maintained equipment or poor quality raw materials.
During the working schedule, the work center may have Quality loss - any time work is done to correct previous work.
Fully Productive time is what's left after you start with the schedule and subtract time "lost" due to availability issues, performance issues and quality issues.
Does this help? You need to adjust the time of the work order until DONE to account for these losses.
If a work order is completed in 1 Hour without a breakdown, without a slowdown and without any rework - FPT was 1 Hour.
If a work order is completed in 2 Hours with 20 minutes when the machine was broken, 20 minutes where the machine worked at 50% capacity and 20 minutes of rework - FPT was also 1 Hour.