TD, arguably, any decision to not fit the latest gizmo on an aircraft will affect flight safety in an environment where everyone else is using the kit. However, the CAA recognises that not everyone can/will comply, so there are procedures in place to ensure that non-compliancy does not increase risk.
Such procedures usually involve barring an uncompliant jet from very busy airspaces, which are 3 dimensional in nature. So flying below or above or to one side or another from the busy airspace will de-conflict the un-compliant jet. The new ground-based radars are backwards compatible so a non-Mode S jet will be seen and controlled/advised as it is now and depending on the nature of that area, another ATC controller will look after the non-compliant jets, so that the busy airspace controller doesn't have to worry about a non-compliant jet on his screen.
I foresee, in the years ahead, airspace above airports such as Inverness and Aberdeen demanding Mode S compliance within their zones and the airways leading to them. Nimrod MR2 will probably not comply, so it will not be allowed to practice approaches there or fly along the airways. Emergencies will be exempt. The effect is increased distance and time to the Nimrod flight and the consequent increased fuel penalty; nothing more than that.
For many years now, the Nimrod has been operating without a Reduced Vertical Separation Minima gizmo, which allows aircrft to fly closer to each other above 30,000 ft (ish). We are not compliant so we cannot now fly up there with the compliant jets without specific authority. I reckon the original cost of fitting the kit has now been exceeded by the cost of the fuel we have needlessly burnt by flying at lower altitudes than fuel efficiency demands.
Flight Safety is not at risk by non-compliance; only efficiency.
Last edited by AC Ovee; 6th October 2007 at 10:13.
Reason: amplification