In the 1990s the gov't began moving away from Mil-Spec standards to use more common Commercial Off The Shelf (COTS) parts to reduce the cost. This change came in 1994 when William J. Perry issued what became known as the Perry Memo.
The new hierarchy would be:
1. Original North American Aviation engineering drawings
Original material callouts.
Original dimensions and tolerances.
Original heat treatments.
Original rivet types.
Original manufacturing methods where practical.
2. FAA-approved replacement materials
If an original alloy is no longer manufactured, an equivalent material with equal or better mechanical properties is typically selected and documented.
3. Industry material specifications
Materials are commonly purchased to standards from organizations such as:
ASTM International
SAE International
The Aluminum Association
For example, an original 24ST aluminum part would today almost certainly be made from 2024-T3, because 24ST was the pre-1954 designation for essentially the same alloy and temper.
Therefore, there may be no existing Mil-Spec, however, the supplier will have to satisfy the nearest applicable/available specifications to comply with the FAA requirements for flight.
Jul 08, 2026 at 02:52 PM
Previous versions of Ray Swindle's message #17068485 « Mustang Air to Air: The Sequel »
