Ron Natalie wrote:

If it was approved on the type certificate, you don't even need a 337.

Which can be a trip. When I bought my Maule, I added a few things as money
permitted. One item was a clock. Chief Aircraft had a model that was on the
optional equipment list. No STC required.

When it arrived, I discovered that they had sent a new model. This one had
internal lighting, which was the only difference. That meant that a 337 had to
be filed, a local FBO had to handle the paperwork (which costs), and the local
FSDO required a field inspection.

All for a stinking clock.

George Patterson
Brute force has an elegance all its own.