With thanks to Dave Reid for spotting this and posting on the "other" forum. One to add to your alerts if you're interested in military aircraft.
From the UK CAA:
With effect from 1 February 2009 the following SSR procedure will be introduced:
Unless a discrete Mode A code has already been assigned, outside controlled airspace below FL 195 and outwith the UK low-flying system, pilots of military fast-jet aircraft should select Mode A code 7005 prior to engaging in sustained high-energy manoeuvres. This will highlight to controllers the nature of the flight. Controllers should expect such aircraft to perform sudden and unpredictable changes in altitude and heading, and should be prepared to react accordingly. Controllers are reminded that the Mode A Code 7005 must be considered as unvalidated and the associated Mode C unverified.
