I am not 100% sure, but if my memory serves me correctly CDAs are required at EGLL below a certain altitude (7,000' ?). I will seek clarification and advise within a few days.
If you need an answer sooner, post this question on pprune.org and I'm sure someone will tell you within a few hours.
Last edited by dundem; 06-13-2010 at 05:41 AM.
Reason: added pprune reference