Traffic Info

[mikk_13]

A Q from an ATC.

Would it/ Is it helpful to get the squawk code with traffic info. Can you see it on your TCAS display? I seem to remember on my jump seat flights that you can see the code, therefore I am wondering if it would be helpful if there are a few aircraft in the vicinity.

thanks

[Denti]

No, we cannot see other aircrafts squawk code on the TCAS display. Dunno if there is any aircraft that displays that kind of info.

[canadairguy]

The AWACS ;)

[Denti]

True enough :)

Just wondering if anyone is using an ADS-B in display that displays more information than TCAS does.

[mikk_13]

Ok thanks for the info.

Onto the next Q, ADSB- you can see the flight id right? Can you see the flight ID if you are out of range of the ADSB ground transmitter, eg acft to acft? or is it acft to ground to acft?

Also, to what range does the TCAS display go? Say I advise traffic is 20 miles 12 o'clock, can you see this on you display. What if the Traffic will pass behind you, can you see this on your display or is it only in the 90 degree/ish arc ahead.

I am interested as it will hopefully give me a better idea on what is useful information to pass as traffic. There isn't much point advising traffic that will pass behind you if you can't see it anywhere.

As pilots, what would you want in traffic info?

I am asking as i had a discussion at work the other day when and what is appropriate and useful when we have 2 that are 5 miles apart. Of course we have a sep standard so tfc is for info only. This is not a scenario where there is a break down of Sep.

thx

[Rainboe]

You can only see traffic on the Nav display that TCAS decides may become, or has become, a potential threat. All you see are the point position, and digital numbers showing how much higher or lower they are than you, and if they are changing altitude, an up or down arrow next to the altitude differential reading. nothing else. Normal displays only indicate threats within a band of 2000' either above or below. Some sets have a switch up or down that will expand the indication band to within 7000' above or below your current altitude, but this is not normally bothered with.

In practice, as only potential threats are displayed, you only see aeroplanes within a short range. On parallel courses, only traffic within a very few miles is displayed. opposite direction traffic 1000' above or below can be displayed 40 miles or so away. So what the pilot sees is a cloud of aeroplanes around him in close range all going the same rough direction, and nothing in the rest of the massive Nav display, and the occasional opposite direction shooting down from ahead at high speed. It gives the feeling that you are in a formation of aeroplanes aall going the same way, with nothing else about.

Would prefer minimal information to locate traffic: Direction/range/altitude differential/ passing in front or behind/type.

[Denti]

TCAS comes in many different variations. I have flown installations that show only traffic in a range of 2,5NM around you and others that show traffic up to 70NM with level ranges between 2000ft and 9000ft (the latter one could be toggled as Rainboe said), traffic displays included in the usual NAV-Display or as after-market installation in the VSI (737 classics).

Usually if the traffic is of any concern to us and within 2000ft of our actual level chances are high we can see it on TCAS when pointed out by ATC, however that is not a foolproof, approved or recommended operation of the TCAS display. When we do get a traffic information we have to check outside the window using our old but reliable eyeballs. Relative bearing, range and altitude is what helps us to identify the target.

By the way, at the moment in europe at least ADS-B in is not really used by airliners, only ADS-B out via Mode S. So we cannot see any flight IDs or additional info, just the position and its threat to us.

[ATCast]

mikk: Onto the next Q, ADSB- you can see the flight id right?
Although flight ID is a part of the ADS-B message, at this moment the ADS-B info is generally not available in the cockpit. For flight ID of other traffic to be displayed the own aircraft needs to be ADS-B IN equipped, which at this moment is rare.

Can you see the flight ID if you are out of range of the ADSB ground transmitter, eg acft to acft? or is it acft to ground to acft?The data can be received either from a ground transmitter (TIS-B) or directly from other aircraft (ADS-B). The advantage of TIS-B is that the ground station can combine ADS-B data with data received from other sensors like radar, but to use TIS-B you need to be in range of the ground station.
Direct ADS-B IN has the advantage that it does not rely upon a ground station, so it works anywhere. The disadvantage is that it only sees ADS-B out equipped aircraft.

The use of ADS-B for ATC and cockpit display of traffic information depends on the availability of an accurate ADS-B signal. At this moment in Europe 20%-30% of the traffic does not have ADS-B out capabilities. Those that do are not certified, so it is unknown whether the sent info is correct. Therefore at this moment it is impossible to rely on ADS-B for ATC or cockpit display of traffic information. From 2015 onward ADS-B (out) is expected to become mandatory for flights in European airspace. By then, all aircraft will need to be certified for operation in an ADS-B environment, and only then you can rely on the information it provides.

[rhythm method]

You can only see traffic on the Nav display that TCAS decides may become, or has become, a potential threat. All you see are the point position, and digital numbers showing how much higher or lower they are than you, and if they are changing altitude, an up or down arrow next to the altitude differential reading. nothing else. Normal displays only indicate threats within a band of 2000' either above or below. Some sets have a switch up or down that will expand the indication band to within 7000' above or below your current altitude, but this is not normally bothered with.

In practice, as only potential threats are displayed, you only see aeroplanes within a short range. On parallel courses, only traffic within a very few miles is displayed. opposite direction traffic 1000' above or below can be displayed 40 miles or so away. So what the pilot sees is a cloud of aeroplanes around him in close range all going the same rough direction, and nothing in the rest of the massive Nav display, and the occasional opposite direction shooting down from ahead at high speed. It gives the feeling that you are in a formation of aeroplanes aall going the same way, with nothing else about.


Close, but in my opinion, no cigar.

As far as I am concerned (and it is obvious that there are several different variations of TCAS installations)...

TCAS on a standard B737 installation as described by Rainboe is shown visually as traffic, above and below, of 2700 feet (not sure where the 2000ft quote came from? Maybe they have a different software? ;)

Also, traffic advisories, etc are based on a TIME to potential conflict, and I quote from our current Boeing Vol 2...

TCAS identifies a three dimensional airspace around the
airplane where a high likelihood of traffic conflict exists. The dimensions of this
airspace are based upon the closure rate with conflicting traffic.
TCAS equipment interrogates the transponders of other airplanes to determine
their range, bearing, and altitude. A traffic advisory (TA) is generated when the
other airplane is approximately 40 seconds from the point of closest approach. If
the other airplane continues to close, a resolution advisory (RA) is generated when
the other airplane is approximately 25 seconds from the point of closest approach.
The RA provides aural warning and guidance as well as maneuver guidance to
maintain or increase separation from the traffic.
Non–transponder equipped airplanes are invisible to TCAS. RAs can be generated
if the other airplane has a mode C transponder. Coordinated RAs require both
airplanes to have TCAS.

[Port Strobe]

Also, traffic advisories, etc are based on a TIME to potential conflict

Is there not a spacial element in the mix too? What's in the Vol 2 certainly isn't wrong but it mightn't be the whole truth either. Not exactly everyday event but if an intruder crept up on you with a decreasing relative speed it may not trigger a TA until it's unacceptably close if based on time alone as a trigger. I was always under the impression it'll shout at you if something gets into either your "time" or "space" bubble, whichever happens first?

[rhythm method]

I would honestly guess (and I stress 'guess') that it is time alone which is used in the calculations. If, as you say, the intruder is creeping up on you with a decreasing relative speed, it won't make any real difference. It is solely down to the fact that there is a closing relative speed, and therefore it uses that closure rate in its' calculation of when to issue a TA or RA.

(I think!) :\

[Capt Pit Bull]

Is there not a spacial element in the mix too?

Correct.

There are absolute minimum protected ranges, within which TAs and RAs are triggered, regardless of the rate of closure.

As an example: Without this, it would be possible for an intruder to slowly merge with you, and then by turning towards you generate an increased rate of closure, triggering a rapid succession through TA to RA but without sufficient time for the RA to be effective.


You can only see traffic on the Nav display that TCAS decides may become, or has become, a potential threat.

Sort of. TCAS only displays traffic that it is tracking full time. The extent to which it tracks another aircraft is a mixture of the potential threat posed by the other aircraft AND the congestion on the SSR frequencies.

In busy environments TCAS becomes more 'picky' about which intruders it tracks continuously, and drops those that are not a potential threat. They'll be dropped from the traffic display and TCAS will 'monitor' them at a reduced interrogation rate, upgrading them back to full time tracking if the situation warrants it.

So, in low traffic densities you may see blips out to relatively long ranges (40 miles or so) that are basically zero threat. As you fly into a terminal area such blips will likely be removed from the display, along with possibly aircraft that are closer but with low closure rates, or even quite close but diverging.

As pilots, what would you want in traffic info?

Depends on the service you are giving me and the service being received by the other aircraft. If we are both under radar control there isn't really that much need to tell us about one another, although it might be nice to be told about him if he is constraining our path; that way we won't hassle you for further climb / direct routing.

I wouldn't recommend any assumption on your part that we can see a particular aircraft on our traffic display. There is no gauruntee we have a blip for it, and also no gauruntee that the blip we have is the aircraft you are talking about.

Basically, the Traffic Display has so many limitations it should not be relied upon for anything. Over use (and over optimism about traffic display capabilities!) is a major concern in TCAS operations.

Hope thats of some use.

pb