This is the usual misunderstanding of CAP371. You can start a flight if you have less than 100 hours in 28 days. So, if on the 28th day you have flown 99 hours for instance you can go flying for as long a single sector as you like, so you might get 110 hours in 28 days perhaps. Likewise with the imagined limit of 900 hours a year. It's actually 900 hours in the previous 12 "calender" months so if you have 890 hours in the 12 months finishing on the last day of the previous month you can operate for the whole of the next month and you might get 1000 hours maybe. Sleep? Who need it?
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