BKS - I can't recall BKS (Barnby Keegan Stevens) flight numbers, only reggies.
Northeast - NE - 'Norjet' / 'NorProp' (?)/ 'Albion' Tridents/Viscounts
Air Anglia - AQ -'Air Anglia'
BIA - 'BritIsland'
I think I need to go up into the loft.........I'm sure that there is a de-code up there fom the early seventies. Funny how one forgets having used them on the Ambers every day (Sector 7/13.....!) Reggies went out when stored FPLs came in. Saved having to refile after an aircraft change.