TCAS II and VFR Traffic.....

[Warped Factor]

.....a bulletin here (http://www.eurocontrol.int/acas/webdocs/ACAS_Bulletins4-BUL2-D-2.0.pdf) from the Eurocontrol website may be of interest. It describes scenarios and answers questions that may be asked by the VFR community.

WF.

[TC_LTN]

Thanks for the link WF. The data re-raises some very interesting points about 'separation' between IFR traffic in Class A/D and 'other' VFR/IFR traffic operating in Class G airspace. I have become increasingly interested in just how we will continue to operate in some of our CTA extensions and some of the airspace sharing arrangements that take place at present, post the introduction of 'compulsory' carriage of Mode C/S. The fact that 500ft does not generate an RA but 400ft does when we, at present, allow a tolerance of plus/minus 200ft on Mode C readouts would be very 'interesting' with ALL aircraft carrying SSR. The other interesting factor is that while even when 'visual' separation is achieved and a pilot judges this to be sufficient that RA action, of course, remains compulsory. At present, a lot of these encounters are never subject to ACAS interrogation and therefore we trust, indeed depend upon a pilot's judgement in being happy with the 'separation' between IFR and VFR traffic. Once all these VFR aircraft are Mode C or S equipped we built in some minimum electronic separation criteria which I suspect are greater than those tolerances accepted by pilots at present. Eurocontrol obviously see this as a significant safety enhancement and a prime reason for the early mandating of the equipment. I am not so sure and think a lot of 'flexibility' in the present operation will be lost or at least tempered by the introduction of an electronic separation tool. I am thinking of several airspace sharing agreements in Class D airspace in the UK that simply will not be able to continue because of the impact of the introduction of compulsory Mode C/S. I would be very interested in other people's views. I wonder if we should be looking to achieve a 'separation' standard between IFR and VFR traffic in all circumstances, anyway, and this is simply a tool to achieve this or is this going to be a major interference in a pilot’s ability to safely separate himself/herself from other traffic in specific circumstances.

[A and C]

Some of us fly aircraft with TCAS and if you have mode "C" selected it is much safer for all of us !

[IO540]

The article is well written but deals mainly with commercial v. GA traffic warnings.

Perhaps it is intended to justify mandatory transponder fitting in all GA aircraft, and certainly TCAS usage where GA is (or might be accidentally, i.e. anywhere below about FL100) flying seems entirely dependent on all GA having and using transponders, which presently is far from being the case.

So I am not really sure what they are trying to say. If everybody has a transponder and has it switched on, TCAS is going to work, otherwise it might not. Outside of CAS, TCAS/TPAS is a waste of £25k, IMHO, before 2008. Even after that, I wonder how many people will be pulling that circuit breaker?

[TC_LTN]

A and C

I have read the above link; I am simply not convinced by some of the arguments.

Undoubtedly, in 'pure' terms, the separation of ALL aircraft has to be safer. What I am trying to highlight is that current practice which is evaluated by comprehensive risk assessment and safety management systems will no longer be possible in a total SSR environment.

Scenario 1: IFR traffic given a closing heading for the ILS at 12 Miles from touchdown while level at 3000ft ALT in a Control Area with a base of 2,500ft. VFR traffic converging and transiting below the CTA at 2400ft ALT whose Mode C is actually indicating 2600ft ALT (within tolerance under current rules) generates an RA Climb to the IFR traffic resulting in the IFR aircraft being above the glidepath and needing to be repositioned on Final Approach.

Scenario 2: Airspace sharing agreement allows a Gliding Operation to 1 mile adjacent and underneath the nominal glidepath of a final approach track used by IFR traffic. ALL of this gliding operation is mandated to carry Mode C or S and starts to generate continual RAs for IFR traffic flying the ILS approach.

[A and C]

I can see why you have your doubts about the system in well regulated airspace such as Luton with the proximaty of gliding as well as a lot of VFR trafic flying along the bottom of CAS however without VFR traffic using the mode "C" I find the workload going into EGCC increases as the system gives TA's for all the traffic in the low level lane using only mode "A".

Most TCAS incidents are TA's and are usualy resolved long before an RA is triggered ( in fact I have never had a RA outside the sim ), so apon reflection I think I would rather in the "real world " have the occasional TA from VFR traffic because at least then I know were that traffic is.

My main gripe about transponder setting is that I have been getting wind if some flying instructors who tell students not to use the mode "C" for fear of getting discovered infringing CAS.

[ThePirateKing]

A and C,

"Getting wind of", you say? Let me tell you it absolutely does happen. On a number of occasions I've selected 7000/C on departure and had various instructors reach over and either reselect 7000/A or simply turn the transponder back to standby. Various reasons given including "no need to squawk in class G", "no need for C outside CAS", etc. Seemed v. daft to me. :confused:

TPK:ok:

[A and C]

Thanks for that , I'm glad that I was not misinformed but it leaves me very worred about the mindset of these instructors.

With so much "fast VFR" traffic ( Turbo-props and small biz-jets)around the London zone it strikes me as a little stupid to not use all the tools that are fitted to the aircraft to keep clear of other traffic.

And before one of you says it "lookout" has to be the primary tool for avoiding other traffic.

[M609]

Turning a servicable transponder to STBY is possibly the most stupid you can do..... :mad:

I little bird in the glider community over here told me last year, that the new SSRs for gliders use so little juice, that there is really no practical reason for not fitting it to all gliders as well. (Not counting cost offcourse)

Me thinks a mandatory SSR requirement for all aircraft will be pushed through via Eurocontrol sooner rather then later.... :E