TA ONLY when operating VFR?

[Linton Chilcott]

Small turboprop aircraft are soon to be mandated to carry TCAS in the UK.

Does anyone have any experience of operating VFR with TCAS, and suggestions whether to select TA ONLY or RA? The regulators don't seem to offer any relaxation from the requirement to select RA, but I wonder whether they have yet considered the VFR case, as larger aircraft (the only ones so far equipped with TCAS) don't very often go VFR.

I can imagine situations where an RA generated by traffic which has been visually acquired, could lead to a climb into IMC while below MSA, which might be unnecessary and unsafe, particularly when operating in mountainous or hilly terrain.

On the other hand, I understand that TCAS can be kept on RA while in the visual circuit, which implies that any RA while VFR will probably be pretty serious, anyway. But, when VFR in the open FIR, speeds are likely to be higher than in the circuit, leading to RAs on traffic that is further away, and may not actually be a threat if it is in sight.

Experience / suggestions / thoughts please?

[GlueBall]

Both modes at all times: TA/RA in all phases of flight! Why would you not want to use the full cabability of the system?

TCAS has better traffic separation logic than your eyeballs. Believe it. :ouch:

[Jetstream Rider]

There have been a number of times when I have seen an aircraft below me, looked on TCAS and it has actually been above. When we get closer, the optical illusion disappears. If you saw one of those coming towards you and got a "traffic" warning because you were at TA only, then you may well climb into his path. What's worse, is you both may climb.

If you have a conflict with say a Hawk while both flying VFR, you are unlikely to see it. In fact when the guys at Valley had some war games with some F15's from the states, the hawks won every dogfight, because the F15 pilots couldn't see the Hawks (they are very small). If experienced fast jet pilots can't see them, then having your system set to RA will definitely help.

What happens if you are flying VFR and get a "traffic" warning (while set to TA) from someone below you who is not actually a conflict - you look out of the window and can't see them. What do you do? Manouevre or not? What if you just haven't managed to see them and they ARE a conflict? I would say RA every time. A brief excursion into cloud (20 seconds say) is less dangerous than the scenarios above.

A TCAS climb isn't a full power EGPWS climb, it may well be just a few hundred feet a minute change, or stopping of a level off.

[BEagle]

Operating under VFR, either in Class D, E, F or G airspace in the UK you may well be in a regime where other traffic is carrying non-Mode C SSR. Or even no SSR whatsoever.

Thus you might receive an RA about someone 400 ft above who you can see isn't any real problem. But you react within 5 secs as taught and descend into someone you didn't know about.

But of course you cannot simply ignore RAs....

Whereas TA only forces you to look for ALL other traffic in VMC before manoeuvring appropriately. Presumably you will be in receipt of a Radar Service (either RIS or RAS) when operating the sort of small turboprop for which the TCAS mandate will apply? If so, ATC should be able to back up a 'Traffic, Traffic' advisory.

There's no obvious solution; however, I think that a habit of ignoring 'nuisance' RAs in Class G airspace would be very unwise indeed. Perhaps better always to use TA/RA in IMC, but to use TA only in VMC even under IFR with a RAS/RIS?

[Fatty]

TCAS 1 is fitted to our little turboprop, and we always fly VFR. The TCAS 1 is the simple one, I think the later TCAS 3 tells you whether to climb or descend.

Anyway, we generally use it as an aid to looking out the (small) windows. The fact that few light aircraft bother to use their transponder, if fitted, means total reliance on TCAS is unwise.

Personally I think a bubble canopy and a decent roll rate is the way to go.

Fatty

[Linton Chilcott]

Thanks for your comments.

I believe we will go for RA always, and see how it goes in service.

A couple of notes:

1. If you are VFR below cloud and below MSA, an RA will not necessarily only result in a climb for a few seconds followed by a return to previous altitude. If the response to the RA leads to a climb into cloud, you will now have to perform an Emergency Climb to MSA (IMC below MSA = not a good idea).

2. TCAS 1: Provides only information.
TCAS 2: Provides vertical manouevre guidance.
TCAS 3: Is intended to provide lateral guidance also. But is not yet in service, and is unlikely to be so for a long while.

[BEagle]

Just be careful that your RA doesn't cause you to react so quickly that you endanger a non-transponding aircraft operating quite legally in Class G airspace!

As I wrote earlier, use of TA/RA in Class G airspace under VFR could be actually prove more hazardous than it is worth. The scenario you suggest (flight under VFR below MSA, RA received, climb into IMC, emergency climb above MSA perhaps with insufficient time to advise ATC......) could all be avoided if instead you left the system at TA only, queried the traffic and then spotted the Cessna 152 which has just selected its SSR to Mode C.

I strongly advise switching to TA only under VFR. You must learn to react instinctively to RAs; however, 'nuisance' RAs in uncontrolled Class G airspace could cause you, your passengers and other legitimate VFR traffic needless hassle.

Alternatively, consider staying out of such airspace?

[GlueBall]

flight under VFR below MSA, RA received, climb into IMC, emergency climb above MSA perhaps with insufficient time to advise ATC......)

RA is performed immediately without first notifying ATC.

...ATC is advised after the fact. :ooh:

[Wino]

Beagle,

Having used TCAS for 12 years, trust me. There is NO scenario where you would want to turn it off. With the lastest software its even used on the close parallel approaches now I think.

You get an RA you carry out the instructions and then simply say. fligiht xxx tcas climbing (or ) descending...

doesnt take long at all. Don't turn it off, dont ignore it or you will end up like the chaps that crashed over switzerland a year or two ago.



Cheers
Wino

[BEagle]

Yes, you do indeed always react instinctively to a RA. Which is fine and dandy in an evironment with all traffic squawking Mode C, but here in the UK it isn't mandatory even to carry a transponder at all at lower levels in Class G airspace. So, if you react to a RA against one aircraft which is squawking, you might actually endanger another which isn't. As well as yourself, perhaps.

TCAS was never intended for use outside controlled airspace, in fact originally it was for use in terminal airspace only, IIRC. So to use it in TA/RA mode in the 'open FIR' positively invites needless RAs against wholly legitimate VFR traffic - as well as giving no protection whatsoever from non-squawking traffic.

[Mr R Sole]

However TA/RA in the open FIR gives you some protection against military traffic. Espeically in the remote parts of the UK!

[BEagle]

True - because they'll normally be squawking. But Golf Alfa Sunny Afternoon Cessna won't be when your inappropriate RA response to a VFR Tornado suddenly fills his windscreen with turboprop airliner....

[Pierre Argh]

Why not use the TCAS in the same way you would call for an ATC Radar Service in Class G. i.e. IMC, when you'd probably be more comfortable under RAS, use TCAS in RA Mode... VMC, or in reasonable conditions when RIS would be sufficient, then use TCAS in TA Mode. That way the end effect would be similar?

[Miles Magister]

I think it is time to post thisACAS II Bulletins (http://www.eurocontrol.int/acas/)
link again.

Go to Safety Information and scroll down to ACAS II Bulletins. I make them compulsory reading for our pilots.

There is some good info on this site.

MM

[BEagle]

Quote: To trigger RAs, TCAS needs intruders to squawk altitude. VFR traffic should be strongly encouraged to operate an altitude reporting transponder in all classes of airspace.

But until they do, I would recommend following Pierre Argh's suggestions precisely.

[Capt Pit Bull]

Linton,

An imperfect situation for sure.

Lots of valid points made by folks already.

The main points to bear in mind are:

1. Disregarding an RA is usually inadvisable. [for those of you reaching for the keyboard and wanting to get stuck into me for not saying ALWAYS, just don't. Use the search facility, read related topics on which I have posted and don't bother replying unless you have something new to say, because its already been done to death]. There are situations where it may be safer to not follow the RA. However, it is ALWAYS a bad idea to manoeuvre opposite to an RA. Hence if you can reasonably foresee a scenario which might cause that, you are better off being in TA only mode, because:

2. TCAS scenarios get more complicated and more critical when one or both aircraft in the encounter have inhibitions (re: possible RAs). E.G. if you are at low level, or a poorly performing light aircraft. Sounds like a factor for your operation. Specifically, being in TA only mode can provide the other aircraft with more options for a succesfull uncoordinated RA.

Linton, I've spent a lot of time thinking about TCAS (it was a project at a previous job for me). As I recall, a while back you passed through an institution at which I was an instructor. If you want to talk TCAS drop me a PM and we'll have a chat.

Regards,

pb

[Daysleeper]

Some of the comments on here make me wonder what pepole think an RA is. It is not a GPWS style max energy pull up. Often it they appear to be very subtle manouvers with level changes of only a few hundred feet or indeed a prohibition to climb/descend.

Don't forget if you have an RA there is a very high chance of collision if you do not follow its guidance.

For that RA to then send you onto a collision course with non transponding traffic is highly unlikely during the very brief time the RA lasts.

I would use it all the time.

And for the really low level stuff it auto switches to TA only below about 1000 feet.

[Mr R Sole]

Since Linton Chilcott is probably referring to operating in the north of Scotland when going VFR I will make a few points that are valid for this area of operation. Military traffic is more of a threat than Mr Cessna so I would suggest that in the remote parts of Scotland then this is when you would use TA/RA.

In the remote parts of Scotland then the Scottish frequency also doubles up as the FIS frequency so if the chap in his Cessna is going to talk to anyone then he will probably be on the same frequency (if they decide to speak). Traffic density is a lot lower then in the south east of the UK and TCAS is a fantastic tool for us when dealing with fast jet Mil traffic that is squawking. These aircraft will not be on the same frequency that you are on so intentions will be unknown and the Scottish controller probably won't have a chance of coordinating or finding our what he is doing.

Busy areas of airspace then TA only but I feel that TA/RA for the ops that Linton is referring to might be more useful!

[Linton Chilcott]

Thanks for your comments.

The point about the pop-up-or-out-from-behind-a-hill fast jet, which we are unlikely to see in time on receipt of a TA, is a good enough reason for keeping TA/RA always on, I now think.

A TCAS climb is unlikely to be a problem for ATC in the open FIR, as we are not likely to be conflicting with their traffic - in fact, we often can't get any service from Scottish at all on the west coast.

For Daysleeper: the "climb" RA may indeed lead to a GPWS type emergency climb - if the RA climb leads us up into IMC while below MSA. This was my main concern initially, regarding TA/RA while VFR.

However, I accept that the initial RA manouevre is not necessarily violent - probably considerably less than avoidance action on a flock of geese or a late visual acquisition of an aircraft, for example.

I gather you need to be really pretty close to a pop up aircraft for an RA to occur without prior TA. If so, the incidence of unnecessary RAs should be pretty slight.

We are, as suggested, using the Eurocontrol Bulletins for training purposes.

Finally, I don't want anyone getting the impression that we spend our time swanning around low level VFR. However, there are occasions when, on balance, we feel there are safety benefits from staying VFR (and being able to see the hazards, such as terrain), rather than being up in the bumpy, icy, clouds, looking for the, procedural, non-precision way down.

[Mr R Sole]

if the RA climb leads us up into IMC while below MSA. This was my main concern initially, regarding TA/RA while VFR.

Interesting point - never crossed my mind!

I used to fly Jetstreams and I had an RA with a Tornado in the Scottish FIR not that long after TCAS was introduced on the fleet. It was by no means the first nor would it be the last RA against Mil traffic! We were IFR but in good VMC at the time.

That example showed me that TCAS is an excellent tool when used in the open FIR when there is fast jet military traffic nearby.

[ShyTorque]

We operate VFR as much as possible. We have TCAS which can operate only in TA mode.

Many of the aircraft our TCAS picks up in Class G doesn't give a mode C readout but I would far rather know there is an transponding aircraft close by than not. I would certainly never switch it off!

[P-T-Gamekeeper]

I operate a military transport with TCAS II. We always use TA/RA whether VFR or IFR.

On several occasions (both VFR) I have responded to an RA that I would have hit had I not done so. Had I been operating TA only, the time it takes to identify & locate the other aircraft may have been fatal.

Beags - If you operate TA/RA, you can manouvre as required, even ignoring the RA if you have the traffic visual and you decide the RA puts you in greater danger. If you operate TA only, you may never get the opportunity. Have there been any crashes where the response to a RA caused the collision? I bet there are plenty where use of TCAS RA mode would have saved lives.

If the RA traffic is below you, or outside your FOV, then RA is the only protection you have. If flying VFR, you should be able to monitor the airspace in front of and above you where TCAS will ask you to fly.

Flying has inherent risks. The open FIR can be a nasty place, where not everybody is playing by the rules. If it was mandatory for ALL taffic, including gliders to squawk mode C, it would improve matters. Cost should not be an issue when safety involved.