Right, I think I've got it:
- Approval for RNav approaches does not automatically include approval for PRNav
- Approval for BRNav and for RNav approaches is quite easy to get
- Approval for PRNav is more difficult to get, for no real reason except beaurocracy
- IO540 assumed, because my aircraft aren't jets, that they're not PRNav-approved
- Bookworm has attended a talk by my boss, and, based on what was said at that talk, believes my aircraft are PRNav-approved
Now that I'm at work, I've been able to dig out a couple of the certificates. In fact, IO540 and Bookworm are both only partly correct - of the first two certificates I looked at, one aircraft is PRNav-approved, and the other isn't! I'm not sure about the other two Duchesses, I'll have a look at their paperwork later.
Thanks! All is now clear as mud!
FFF
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(PS - Jan, I started typing a reply to your question then lost it by mistake, haven't got time to re-type it now. I'll answer it later if no one else gets in first.)