SOU has a 5,653ft runway, it's primary destinations are the CI, both ACI and GCI have lesser length runways so nothing achieved by extending the runway at the SOU end and not t'other end of the route(s), JER has a slightly longer runway but one can operate B737's SOU to JER (I know because we did it) so nothing achieved in extending the runway for JER operations, Eastern Airways hardly need longer than the existing SOU runway and that leaves FlyBE who have various sizes and types of equipment whilst they chop and change their routes, so all they need to do is allocate the appropriate equipment to the appropriate SOU route and everybody lives happily ever after!