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

How not to do it ( video ):

Kamera fällt während Aufnahme aus Flugzeug

The device was found by a pedestrian about four month after it fell off a gyrocopter. Now they want to know who is missing his camera...

skadi

Sorry guys really late to this one but

I was the pilot that dropped Gary Connery with no parachute into 18000 cardboard boxes. We had go pros on the skid ( clamp, backed up by 3 miles of duck tape) one attached to the airframe clamp and duck tape ) one on my helmet and one on the cargo hook.
The CAA inspectors were there in force, I asked them if this was legal in front of a load of people there view was as they were not permanent fittings and removable there was no problem ! So that is it from the horses mouth
Health warning here though be sensible with what you do and have a couple of attachment methods including wire locking !

It used to be that anything fitted externally, according to the UKCAA was a major modification, I doubt that has changed since I retired.

Oldlae
There you go, you just hit the nail on the head. "according to the UKCAA", but not according to LEGISLATION.