Frontlefthamster, I'd like that pointed out in writing in a piece of regulation and law, please, because the law [using UK ANO, not EU ops this time] only specifies that minimum equipment as required by the law has to be carried and servicable. I might have overlooked the paragraph actually prescribing that ALL equipment has to be serviceable for private ops, could you point it out?
On the other hand, EU OPS for non-commercial operations says
A flight shall not be commenced when any of the aeroplane instruments, items of equipment or functions required for the intended flight are inoperative or missing
(my bold). It says required. Not installed, required. If they meant installed, they surely would have said so?
You also asked where in the POH it says which equipment may be unservicable. It is the other way round - it says which equipment MUST be servicable. And there are plenty of examples - the two Piper POHs I have to hand say that required equipment is as required by the regulations, and the SR22 and Beech Baron POH I have in front of me contain MEL-style lists, for example in the Cirrus you must have 2 alternators and 2 batteries for IFR, but only one for VFR - which is an addition to equipment required by law due to the type certification as an all-electric airplane.
Of course if you want to fly with
less you need an MEL.
I only believe your suggestion, that you could not fly an aircraft if the cigarette lighter, cabin fan, or the electric trim, or even the autopilot are defective when you can quote regs - experience and training don't count.