We don't use "hours" in our 1.D.2 as DAL does. We use hulls, then define them.
"Parking" is when the airworthiness certificate lapses, or in the case of "heavy checks" (which might allow a cert. to lapse), we use insurance status.
None of our DC-9's carry hull insurance, since none of them are leased (they're all owned). ALPA tracks the liability insurance status of each hull through the underwriter. (We have a full voting memeber on the NWA Board of Directors) On any given day we'll have 2-3 hulls that are not flying for OTHER than mx issues. They're active aircraft, but used as spares.
The "inactive" aircraft list is published once a quarter, but is only a general reference. Management must comply month-to-month.
As with most limitations in the PWA, this is one that we've had to tighten over the years dueto management's creative interpretations.
Thanks for the info.