Mandate the carriage and operation of Mode S transponders on all aircraft operating within controlled airspace of classification A to E.
The aim of this Option is to create an environment where the position and altitude of all aircraft within CAS is ‘known’ to ATC and TCAS systems. Well, the position of all aircraft is already known to ATC through radar control or procedural clearance because that is what CAS is about. If we were flying in IFR, interacting with TCAS would form a sensible safety net but if we are VFR, we have visual sighting aided by traffic reports as a safety net in the rare case that radar control or procedural clearance breaks down. VFR aircraft flying under control within CAS do not need to be interoperable with TCAS to maintain the target level of safety. This is already accepted in principle because we are told that non-transponding aircraft will be able to gain access through agreements or exceptionally through temporary ATC clearance. Indeed in the series of roadshows the CAA team has been quite positive about the continuation of ATC clearances as they are today. If it was less safe, that would not be proposed or allowed.
So we have a situation proposed where Mode S is essentially optional.
So perhaps we should look at a real alternative to the way this is set out whilst still achieving what the CAA expect from this policy. None of us would disagree that Mode S should be mandated in Class A airspace and for IFR flights in Class B to E airspace; TCAS can then form a backstop safety net against collisions with CAT. There appears to be no safety case to argue against VFR flight, subject to ATC clearance, in Class B to E airspace for the reasons above using visual sighting as the safety net. As we all know, clearance is easier to obtain with a transponder than without, so recommending Mode S would be straightforward and none of us would challenge such a sensible policy. This would satisfy the CAA’s remit from the Transport Act 2000, “to satisfy the requirements of operators and owners of all classes of aircraft” and it would do so without compromising safety. The consultation points out that as airspace becomes more crowded, clearances will become more difficult. Well, no problem with that; if you want a clearance through busy airspace you will have to install a transponder but that will then be your choice and your own business case for the costs.
Therefore an acceptable alternative might then be that Mode S is mandated in Class A airspace and IFR in Classes B to E. For VFR flight in Classes B to E with ATC clearance and control, Mode S could be recommended, noting that without a transponder, access will be more difficult than with. To improve interoperability with TCAS systems we also propose that approvals be removed from transponders without Mode C.
But the overarching requirement must be for reasonable access for VFR flights in Class B to E airspace for those aircraft without a transponder.
Option 1 - Option 2 - Option 3 - Option 4