TCAS RA vs visual on traffic

[xma05]

If you have a visual on traffic and still get a TCAS RA should it be followed?

I know that you can confuse the traffic and RA could be caused by something else, but let's look at a this scenario, that I take back from my PPL training in USA. I was flying a Diamond DA-20 at 2500 MSL and a 737 joining the downwind on a visual approach passed right below me at 2000ft. The separating was 500 ft. ATC had advised him of me and he had me in sight, I didn't see him until he was almost under me because he came from under my wing (from my 8 o’clock). Do you think he had TCAS RA? I had mode C and TIS installed in a Garmin 430 and had TA on him, but TIS (traffic information system) is not a full TCAS.

Recently one of the captains in our company flying a regional jet had a similar situation in Germany. ATC made sure he had a visual on small VFR traffic and patter after which he was cleared for approach and he had RA with, which he did not follow, as he had the traffic in sight. Was he right in your opinion?

I didn’t find any manuals recommending the course of action in that kind of situation.

[Daysleeper]

Always follow the RA.

he had RA with, which he did not follow, as he had the traffic in sight. Was he right in your opinion?

No he was absolutely wrong.

The visual assessment of traffic can be misleading. At high altitude, it is difficult to assess the range and heading of traffic as well as its relative height. At low altitude, the heavy aircraft attitude at low speed makes it difficult to assess whether it is climbing or descending.
• Visual acquisition does not provide any information about the intent of other traffic.
• The traffic in visual contact may not be the threat that triggers the RA. A visual manoeuvre relative to the wrong visual traffic may degrade the situation against the real threat.

Eurocontrol stuff via skybrary

[grounded27]

It sounds like he may have been in a tough position, sounds like ATC probably screwed up allowing you both there in the first place. There is an operational floor to TCAS, believe it is 1000 feet but an RA will not command him to penetrate that floor (terrain over plane).

I am just saying it is more compicated than you have been told thus far.

[ford cortina]

Not responding to a RA kills people.
Here is the wikipedia page on this very high profile case:
2002 Überlingen mid-air collision - Wikipedia, the free encyclopedia

Your Captain was wrong. End pf

[Piltdown Man]

Do you think he had TCAS RA? I had mode C and TIS installed in a Garmin 430 and had TA on him, but TIS (traffic information system) is not a full TCAS.

No - you only get a RA when the other guy also has TCAS. He may have received a TA "Traffic - Traffic".

Was he right in your opinion?

No he wasn't - you don't always see the traffic that generates your RA.

PM

[Dan Winterland]

Altitude on the dispaly is very accurate, azimuth not so. It can be up to 30 degrees out which leads to the risk of visully aquiring the wrong target.

Alway follow the RA.

[grounded27]

What RA??? do you think he had one?

[de facto]

Follow the RA!!
You may have a traffic in sight but yet another is causing the RA.
Visual own separation should not be imposed upon the crew just because ATC lost their separation minima.
I believe vmc daylight and be damn sure u are loking at the correct traffic is somehow a prerequisite to 'accept' such a clearance.
Wake turbulence is not obviously provided.
I suggest a safety report .

[splitduty]

de Facto,
Would you like to advise what `separation minima` you expect ATC to provide between IFR & VFR flights?

[xma05]

No - you only get a TA when the other guy also has TCAS. He may have received a TA "Traffic - Traffic".

You get TA, when another aircraft is XPDR mode C equipped, which my aircraft was. And as I understand you should get RA when another aircraft is within 600 ft even if both aircraft are in level flight, however 500 ft separation is sufficient between VFR and IFR traffic provided both are in VMC and have each other in sight. So it doesn't make sense to me.

[Piltdown Man]

Firstly, I apologise for my initial post - It should have said RA and not TA.

And as I understand you should get RA when another aircraft is within 600 ft even...

That was the minimum margin of separation for TCAS I. But TCAS II attempts to keep a 20-30 second margin between the two aircraft in an RA. But both people HAVE to have TCAS. You will not get an RA is the other guy just has Mode C.

PM

[BOAC]

xma - who trained you?

[Brian Abraham]

Two aircraft (Super Constellation and 707), with 1,000 feet vertical separation, managed to collide in visual conditions due to optical illusion (sloping cloud deck). Probably wish they had TCAS back then. Another Captain Haynes story on the Connie flight deck.

TWA Flight 42 - The Unexpected - When Experience and Airmanship Really Counts

[Tarq57]

An aircraft with TCAS can receive an RA in respect of non-TCAS equipped traffic. All that is required is for that traffic to have a working mode C transponder. (And be on a conflicting flight path, of course.) I've seen this, twice. (Works a treat, by the way.)

Regarding the OP, I doubt that the Boeing received an RA in respect of the approach underneath you, unless he was closing on you, and closer to your altitude than 500 feet, and within about a mile. (Or, 20 seconds to point of closest passing, to be more accurate.)

TCAS does not measure "separation" in terms of feet or miles. If that was the case, there would be either numerous false alarms in the circuit area, or inadequate protection at cruise speed. It measures the projected hazard in terms of closure rate based on time.

[de facto]

Split duty,


I know what separation i need in the environment i operate in.IFR radar controlled,single runway,parallel,dependant,independant and segregated.
Now,i dont accept visual own separation POINT.

[splitduty]

de Facto,
you do not mention if you are operating in class A airspace - I assume you are?
However, the ORIGINAL question was regarding operation in airspace with mixed VFR/IFR traffic. A completly different scenario I suggest and that is why I requested clarification of your reply .

[xma05]

In the first case I was operating near KISP class C airport at 2500ft and South West 737 was at 2000 ft. He passed right under me (it does happen).

In the second case, the Captain was operating near Hannover (EDDV).

[Capt Pit Bull]

From the top:

xma05

Do you think he had TCAS RA?

Probably. Difficult to be certain as the numbers you give are close to the edge of the vertical threshold. If you were both in exactly level flight, then yes. But a slight climb on your part or descent on his would have nudged you outside the threshold. So, how accurately were you both flying? (perfect I'm sure).

However, it would almost certainly have been a preventative RA directing him not to climb, so maintaining 2,000' would have been in compliance

(corrective threshold at low level is 300' predicted vertical separation at CPA. Preventative threshold 600')

Daysleeper

Always follow the RA.

Adopted dogma post Ueberlingen. There are in fact a number of circumstances in which following the RA is not the safest option. This topic debated at length over the last decade (see tech log, search for my user id). Contrary to common misconception TCAS does not fully pretect the flight envelope in most installations and therefore your primary task is, as ever, to protect the flight envelope. Within those constraints the RA should be followed.

Your comments on visual spotting are ... spot on

Grounded27

There is an operational floor to TCAS, believe it is 1000 feet

Yes, various inhibitions kick in at various radio altitudes

but an RA will not command him to penetrate that floor (terrain over plane).

Depends. If there is an EGPWS in the mix, and if it's position is accurate and if it's database correct then you should be safe. However you'll notice a lot of if's in that statement. If your EGPWS is degraded back to basic GPWS it is entirely possible for an RA to put you in terrain.

ford cortina

Not responding to a RA kills people

Again, a very commonly held misconception. The facts are: not complying with an RA introduces a risk. I don't have the figures to hand but IIRC its around 2%. This is of course extremely serious but its a long way from certainty.

What adds massively to the risk is if either aircraft manouvres in the reverse sense. Then the risk skyrockets upto about (iirc) 60%.

The problem at Ueberlingen was not a failure to comply with an RA, it is that the Tupolev crew manoeuvred in the opposite sense to their RAs, not just once but twice. They descended when being RAed to climb, and they then increased their descent rate when told to increase their climb rate.

Not that I'm not saying it is ok to disregard RAs. But what I am saying is that as professional pilots we have an obligation to understand the relative risks associated with manouevres.

If you want to survive a TCAS incident here is what you do:

1. First and foremost - never manoeuvre in the opposite sense to an RA.
2. If you get an RA follow it if you possibly can.
3. if you can't follow it get as close as you can.


Piltdown Man

No - you only get a RA when the other guy also has TCAS. He may have received a TA "Traffic - Traffic".

Incorrect. To be able to generate an RA, TCAS needs the intruder to have an ICAO compliant transponder that has encoded altitude data (i.e. mode C with the altitude reporting turned on.

The only thing you need the intruder to have TCAS for is for the RA to be coordinated.

Everyone else: Items covered above.

pb

[629bus]

ALWAYS follow the RA. You "may" not even be looking at the correct aircraft!!

[grounded27]

My point being a fully equipped aircraft flying below you at 2k AGL and yourself with TA only at 2.5k AGL. The 737 probably only recieved a TA as the proper response of an RA would dictate him to decend pushing the terrain floor limit. If this logic is true you are visual with only a command response as the resolution, ATC should not have allowed you into this stickey situation as they are far more closely monitoring traffic at these altitudes within close proximity to an airport.

Follow your RA??? What RA? You are visual and at the mercy of ATC at these flight levels. Eyes on the sky fellas...