Because it it illegal to log P1 U/S as per Rule 67a (quoted in the 2nd post on this thread).
However, Section M of the Schedules of the Aircraft Rules state:
(e) Experience— He shall produce evidence of having satisfactorily completed as a Pilot of an aeroplane not less than one thousand five hundred hours of flight time of which not less than one hundred fifty hours flight time shall be in the preceding twelve months and his total flying experience shall include —
(i) not less than five hundred hours of flight time as Pilot-in-Command or as Co-Pilot performing, under the supervision of a pilot who fulfills the flying experience requirements of a check pilot, the duties and functions of a pilot-in-command provided that at least two hundred hours out of these shall be cross-country flight time, including not less than fifty hours of flight time by night.
Note— Where an aeroplane is required to be operated with a co-pilot in accordance with the provisions of the Flight Manual of the aeroplane, not more than fifty percent of the co-pilot flight time shall be credited towards the total flight time required for the issue of the licence, but not more than fifty percent of the co-pilot flight time under supervision shall be credited towards pilot-in-command flight experience required for issue of the licence, and full credit for such flight time shall be given towards total flight time required for issue of the licence.
That's why a separate logbook indicating those times.
My Question: What defines "duties & functions of PIC"? Is a take-off/landing mandatory? A PIC need not necessarily perform a takeoff/landing without losing his privileges as the PIC of that aircraft.