Compulsory for IFR in controlled airspace either this or next year. 2008 for everyone else out of controlled airspace.
It tells:
height
a/c type
owner of a/c
and I think there is room for other info too.
Not cheap to fit...GAT will be hurting (£)
ATC aren't too happy, their screens will fill to bursting with extranneous information, which is why there is a lead in for all the other 'riff raff' in 2008
