50% of the time
International Trader,
The calculation of aeronautical experience was only for the purpose of satisfying the required hours for the granting of a licence. The 50% rule was only about trying to ensure that the applicant for the licence had done a significant part of their flying in an active role, which for a co-pilot was presumed to be only half the time on a presumed 'leg for leg' basis.
Once a pilot had qualified for the ATPL, 'aeronautical experience' per se had no further relevance...
Stay Alive,