The 'i' doesn't stand for anything but there's a pretty good reason for it.
Apparently in the US, BM is a common abreiviation for bowel movement (ie havin a dump)!
I doubt Bowel Movement British Midland would go down well with the Yanks!
Oh and whoever started the topic and asked when the 1st Transatlantic flight is:
Because of late delivery of the a/c (by Airbus), the 1st flight to Washington will now happen (hopefully) on the 12th of May (it was supposed to be the 30th of April).
1st Chicago flight is around 21st of May.
As for the ads...well, perhaps bowel movement would have been appropriate...
Jamie.