The flights I have searched do usually involve a combo of mainline/express but the seat maps for the inidividual flights on mainline A/C show no F seats available, even on the combined routing. Ironically, my typical return trip ORF-PHL-CLT on 1776/1165 are both mainline A/C (1165 being the dreaded 8F 75) does show F available. Will have to keep looking but to have to search the individual segments for availability on mainline A/C makes for extra work. As I mentioned, this is the first I have encountered this phenomenon so perhaps the website has changed. Thanks.