Does anybody have any idea why the last IAH-ORF and than early morning ORF-IAH is occasionally operated by a Boeing 737-500 instead of the usual RJ145? I don't know how many CO flights ORF sees per day but I'd guess at least a dozen, normally all operated by RJs. There doesn't seem to be any pattern to it, it seems completely random, occasionally CO subs a 735 for the last Houston turn. Do they do this on the fly so to speak if there's unusually high bookings or is there some other method to this? I'd love to see mainline service to ORF on permanent basis, DL, US, NW, and WN (kinda a given I know) all operate mainline equipment.