Hi. .. ." As far as the instruction - " line up on RWY ... at your discretion " ". .. .As expalined already , coming from an A/G unit this is definately a no no. However it's also technically incorrect coming from a FIS. . .. .FISOs will use "Take off at your discretion" when there is no air traffic reason that an aircraft can't depart. . .. .If a FISO wants an aircraft to line up on a runway and wait (perhaps due to traffic wanting to cross the runway, or to traffic departing from further along it etc), the phrase "G-XX, report lining up" is used. The aircraft should not then report until "Take off at your discretion" is issued.. .. .Cheers