"Andrew Gideon" wrote in message online.com...

It sounds from the above like an STC is required before any major alteration
because it "provides authority to make the major alteration". Is that
right?

An STC is one way of getting approval for the alteration. Other "data
acceptable to the administrator" is allowed as well. This is called a
field approval (or sometimes incorrectly, a one time STC).

A lot seems to hinge on the distinction between "major" and "minor"
alterations. What is the difference? Given a particular change (ie.
replacing a panel overlay, or adding instrument lights), how does one know
into which category the change falls?

The definitions are here (I'm not going to post them inline as they are a bit long):
http://www.access.gpo.gov/nara/cfr/c...4cfr43_00.html

Some of it is a gray area. Somethings people read more into it than others.
For example, just because something changes the w&b, it is not a major
alteration. It is only a major alteration if it changes the permissable envelope.