Just my thoughts on some of the comments above...
1/ Bargain basement fares ? The £29 fare that used to be available on Bmi has disappeared ,the lowest I have seen is £37 and this is ex Bhd only due to the airport charging system.THis is comparable with the leadin fares on other Ba domestics and the fares get substantially higher when you get closer to dep.
2/ The 0635 dep on a Sun morning is too early for point to point ,only of use to connectors so will never be busy apart from some dates in peak summer. I presume it's a daily arrival slot at LHR , so they have to op on Sun as well and they want to get the a/c into the system at LHR rather than have it sit on the ground at BHD.
3/There are lots of cabin crew and pilots who live in N.I. but they are based at LHR as there is no crew base in Belfast ,so all crew operating will have originated the trip in LHR even if they happen to be from N.I.
4/The winter schedule with 2 nightstops on some days ends this weekend.
The winter schedule was a bit of a hotchpotch ,utilising odd unused slots acquired from BMI.Some of these will be in the package of slots handed over to Virgin Little Red to op Abz,Edi so the summer schedule is smaller and more regular.There are 6 flights a day M-TH, 7 FRI and 5 Sa/Su and only 1 nightstop.
5/Incidentally , one nightstop will still require 2 crews overnighting in Belfast each night as the crew operating that last LHR/BHD cannot op the first BHD/LHR the next day due to crew rest requirements.
6/Using a larger aircraft at lower frequency would actually increase the number of crew overnighting as there are more cabin crew on each flight . The reduced frequency would be less attractive to the targeted business traveller and less competitive against EI. The larger aircraft would also have to be taken off another BA route where it can probably make more money for BA.