On various matters, this is where I come out for the UK. As it is a long post, I state my conclusions first, and quote the UK ANO bits at the end. I am a bit disappointed that previous posters have not answered all the points in my post number 16, so what is here is my own interpretation for those gaps. Please feel free to correct, with legal quotes, anything I have wrong.
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Signing out as PIC: no legal requirement to do so.
Techlog to show PIC before the start of a flight: no legal requirement to do so.
In GA power: take off with one person (A, say) as PIC; and hand over to another (say B) during flight, without landing between: permitted (Note 1 below).
Each would log (in their personal logbooks) their own time as PIC. (Note – PIC is not the same as PF.)
AIUI, any PPL can let somebody else fly, but remain PIC. (Note 2 below)
If a second (licensed) pilot is on board, and has access to sufficient controls, he/she can if they agree take over as PIC. If they do not so agree, they cannot be made to. (See Note 3 below).
This does not preclude them taking over anyway, e.g. in case of incapacity, or to save their own skin under the general exemption for emergency covered by the ANO.
In UK gliding, the ANO exempts gliders from some of the above. I do not propose to dwell any more on that in this post.
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Note 1, re A as PIC handing over to B as PIC during flight, without landing between.
My conclusion is drawn partly from the ANO, and partly from the general UK law principle that something is permitted if not specifically forbidden.
First, this is not permitted for public transport:
“Public transport – operator’s responsibilities in relation to crew
95.—(1) The operator of an aircraft registered in the United Kingdom must not permit the aircraft to fly for the purpose of public transport without first designating from among the flight
crew a pilot to be the commander of the aircraft for the flight.”
Second, I can find no similar limitation for private flights as in most GA. Therefore, PIC can change during flight for the latter.
Each would log (in their personal logbooks) their own time as PIC. (Note – PIC is not the same as PF.)
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Note 2, re any PPL can let somebody else fly, but remain PIC.
The PPL must remain at the controls:
“PART 6
Flight Crew Licensing - Requirement for Licence
Requirement for appropriate licence to act as member of flight crew of aircraft registered in United Kingdom
50.—(1) Subject to the exceptions set out in articles 51 to 60, a person must not act as a member of the flight crew of an aircraft registered in the United Kingdom without holding an appropriate
licence granted or rendered valid under this Order.”
But nothing here or elsewhere that I can find precludes allowing a non-flight crew member (i.e. a passenger) also being at the (duplicate) controls, as long as the PIC can keep control too.
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Note 3, re a second (licensed) pilot is on board, and their responsibilities.
If they do not agree to act at some point as a member of the flight crew before the flight begins, they cannot be made to. I am sure that UK common law or something precludes anybody being forced to undertake a responsibility like this if they have not so agreed first.
Furthermore, if such a second licensed pilot is present, and has the same or more qualifications as the nominated PIC, that is fine. The second person does not have to be a member of the flight crew, regardless of how highly qualified they are.
If they agree to be part of the flight crew they do not have to be PIC (e.g. they could be radio operator), again regardless of how highly qualified they are.
If they agree to be PIC for part of the flight, they can. This covers the case of the IR person becoming PIC when the original non-IR pilot is approaching IMC. The changeover should be before IMC is entered, if foreseeable. If not foreseeable, it is an emergency and the usual exemption applies anyway.
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Chris N