"Martin Hellman" wrote in message

When I changed my German altimeter for an American made one, I needed
a 337! Unscrewing three screws, pulling out an altimeter, putting in
another, and rescrewing three screws is a major modification to
airframe??

Nope, not in my opinion it's not a major alteration. (43 Appendix A)

Sometimes some guys (including A&P's, IA's and sometimes even the FAA dudes)
don't read the rule, sometimes they rely on memory, what they were told,
what the guidance says, etc. I'm guilty as well and have learned to go back
and read the rule - some rules are very clear, others not.

Swapping an altimeter for another one, especially if it's TSO'd, does not
meet the definition of a major alteration. If your glider is experimental,
you need not be in 43 at all. (43.1) But you do need to comply with the
operating limitations.

Jim