n.b. also that the EU-wide law on mobile workers in aviation prescribes a minimum of:
- 4 weeks (24x7) of paid holiday
- plus 96 off days
for every calendar year.
That is the mathematical equivalent of all annual weekend days after having subtracted the 4 weeks of leave. No OFFs for national/bank holidays. Spread evenly over a year (not a realistic scenario), that leaves almost exactly 20 days for duties in each of the months. Thus 75% part-time yields 15 workdays on a long term average - no charity, just crunching numbers.