Ron Natalie wrote:

An IA must sign off the 337, which is required of any major alteration.
An STC
provides authority to make the major alteration. A minor alteration
requires neither a 337 nor an STC.

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?

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?

- Andrew