Chopjock,
-with the FAA, the rule is, (simplified wording): if its on the outside of the airframe and effects the performance, you need an STC. FAA stc's are recognized by most agencies via reciprocal and/or submission of the same data for approvals in other countries
- we could go on for days about wording and regs, also depends on where your feet are planted and the aviation agency you work with. our customers (literally world wide) demand an STC about 90% of the time, so im going take and educated guess and say, its a requirement
cal