Mode S & latest GASIL
In the first CAA consultation on Mode S when they were in their "compulsory Mode S for all flying objects" phase, one of the objections raised was that a large number of aircraft transponding in close proximity such as a gaggle of gliders in the same thermal would blot out or otherwise interfere with radar returns etc.
That was, if I remember correctly, pooh poohed in the CAA's response.
However in the latest GASIL (3/2008) - a CAA document - we have a section labelled "Formation Flying" which states
"Two or more transponders transmitting in close proximity will garble (interfere) with other transmissions and present an air traffic controller (or an aircraft fitted with a collision avoidance system) with confusing or sometimes false information"
The GASIL article goes on to specify that only one aircraft in a formation should transpond and that the other aircraft should switch theirs off until they separate.
Is this the CAA getting their wires crossed or is this a Mode A/C problem only?