What do the OEMs typically say about PMAs?

Some of them threaten to void the warranty if PMA parts are used, particularly on engines. They often claim that PMA parts don't undergo the same level of testing as OEM parts. Interestingly, we're a large lamp distributor representing most lighting manufacturers except GE. Some airlines insist on using only GE light bulbs, claiming they're the only manufacturers. This is a misconception from 50 years ago when GE was indeed the first lighting company. No one tests lamps in the industry. Every manufacturer uses the same part number for the lamp.

What are the characteristics of a bad PMA? What's not a good category?

A bad PMA would be if you go back, and I hate to use the term, to 9/11. Everyone who was flying an MD80 on September 10 was selling parts. On September 11, most US airlines grounded all the MD80s. So if you were only selling MD80 parts, you would have gone out of business within a few days. That's the only downfall to the PMA; fleet reduction or getting rid of those aircraft for newer ones.