Mr Angry -
After an hour or so trawling through various websites and complex European Union legislation documents to find the answer, the following 2 give a fairly good summary :
1)
DTI Working Time Directive Summary to January 2005.
2)
CAA Fodcom 29/2003
In short, airline crews (aka mobile personnel) were originally exempt from the Working Time Directive when it was established in 1993. Amendments in 2000 decreed that the WTD should be extended to include mobile personnel and member states would have until December 2003 to implement this. This limited annual duty time to 2000 hours.
Additionally, the CAA document states :
...the first and second editions of CAP 371 quoted duty limits for 7 consecutive days, but for convenience and familiarity reasons referred to these 7 consecutive days as a ‘week’ or ‘weekly’. It was decided that the third edition of CAP 371, first printed in May 1990, would (only) define a ‘week’.
This therefore allowed Companies to define their own week, Monday to Sunday in Flybe's case. This wasn't a problem at that time, the CAA document goes on to say :
At that time it was not envisaged that the medically agreed quoted maximum allowable duty hours would be achieved.
But as we all know some Companies now roster right up to those limits as a normal practice, which means, as the CAA document explains:
Because of the definition of ‘week’ it is possible, for example, to start a series of 7 consecutive duties commencing in mid-week of the first ‘week’ and continuing to mid-week of the second, without a break. The total duty hours achieved during the first ‘week’, i.e. for example on days 4, 5, 6 and 7 of ‘week’ 1, would be below the total hours allowed for a ‘week’ (55). The series of duties would then continue into days 1, 2 and 3 of ‘week’ 2 and again the total hours achieved would be below the total hours allowed for a ‘week’. However, the overall effect of this is that in the 7 consecutive days the total duty achieved may be well in excess of the defined weekly limit of 55 hours. Whilst this use of the rule is potentially contained by the existing two weekly limit, it has been reported to the CAA that some flight crew members have been rostered for and are achieving some 75 hours duty in 7 consecutive days.
So CAP371 reverted to talking in terms of consecutive days, and at Flybe this meant having to abandon the practice of resetting the cumulative duty hour clock on Monday mornings, so a 7 day stretch was no longer productive for the Company as it was not really possible to do a normal duty everyday without exceeding the maximum allowable hours. Days 1 & 7 were therefore effectively limited to positioning duties only.
This is why the 7 on 7 off became 5 on 5 off.