BRU seems to be an especially difficult route to break into as the market from/to the UK is shrinking in pax number terms.
I have looked at 2001 when CWL still had a year-round service to BRU. It was operated on behalf of BA using I believe J 41s. There were two rotations on weekdays and one on Sundays.
In that year 20,534 pax were carried on the route giving an average load throughout the year of around 18. If Eastern could have carried this sort of load on their Jetstreams I suspect they would have been very satisfied.
In 2001 the UK-Brussels routes carried 2.44 million pax but the figure has dropped each year since then, and by 2005 had dropped to around 1.52 million pax. As an example, in 2001 BRS carried 93,000 on its BRU route but by 2005 this had dropped to 63,000 (albeit there were more rotations on the same equipment in 2001).
In February this year Air Wales tried the route again, having tested the water a year or two before for a relatively short period. The RDF may have encouraged them to try again but their only full month on the route before going out of business was March in which they carried 1159 pax, an average load of around 12, assuming all timetabled sectors were flown (I have an idea they weren’t so the actual average load would have been a little higher).
Eastern’s short tenure on the route this summer reveals 509 using the route in June and 492 in July, an average load of 6 or 7.
All this seems to confirm the argument that BRU is primarily a business route (from anywhere in the UK) where loads will not be high. One would think that Eastern would be the airline that might have made the route work.