TCAS (traffic display) for FSX ATR 72

[flyatr]

Hi folks,

I have uploaded my little traffic display gauge: ATR 72-500 Vertical speed indicator / VSI with traffic display
It's not a TCAS as it will not generate any warnings. On the ATR this display is included in the VSI vertical speed indicator.

preview.png (36 KiB) Viewed 3261 times

To make it work you need to install an XML gauge to FSX. Download from my OneDrive: https://1drv.ms/u/s!An79_6jJO4vrjexBuONeE79ZzKq2Uw
Installation instructions included in the download

NOTE: This gauge can be freely used by others who want to build their own TCAS. The gauge simply copies the AI aircraft info from the "fs9gps" module into local variables. As you know you can access these through Air Manager. For performance reasons I have limited the number of aircraft to 10 but you could change that in the XML code.

Code: Select all

fsx_variable_subscribe("PLANE ALTITUDE","feet",
"PLANE HEADING DEGREES GYRO", "degrees",

"L:TCAS_bearing_1", "degrees",
"L:TCAS_distance_1", "feet",
"L:TCAS_altitude_1", "feet",
"L:TCAS_vSpeed_1", "feet per minute",
"L:TCAS_airspeed_1", "knots",
"L:TCAS_flight_number_1", "number",

"L:TCAS_bearing_2", "degrees",
"L:TCAS_distance_2", "feet",
"L:TCAS_altitude_2", "feet",
"L:TCAS_vSpeed_2", "feet per minute",
"L:TCAS_airspeed_2", "knots",
"L:TCAS_flight_number_2", "number"

and so on

[JackZ]

Good Job!

I can now figure out why you dropped the idea of a complete TCAS with real Traffic and Resolution advisories. The logic behind this is quite complicated, and most of it, involves an electronic dialogue between the two (or more) TCAS equipped aircrafts in conflict, so they coordinate their action, one thing obviously not feasible with those “dumb” AI airplanes...
Had a look at the theory of TCAS system, quite informative, but extremely tough to implement even partially in AM, not worth the effort aniway?
https://www.faa.gov/documentLibrary/med ... ooklet.pdf
Was wondering if any TCAS gauge do exist in the sim add on world?
I really doubt it.

Keep up the good work!
Jacques

[frumpy]

Well, a "dumb" TCAS should be possible just by calculating whether the other plane got in
the zones and issue a decend/climb command?
I believe Aerowinx PSX has TCAS simulated on both conflicting aircraft.

I think a TCAS would make sense, even if the other aircraft is dumb. I mean by using
just the altitude difference good results should be possible. Just think about a 172 getting
in the way, the airliners TCAS would find it's way anyway.

[JackZ]

By ”dumb” plane, I mean that AI plane which not aware of our position nor intentions will proceed to their predefined trajectory no matter what.

IRL a manned C172 would probably do and try something, even dumber, and of course this kind of G.A. airplane is merely equipped with a Mode C transponder, not a full featured TCAS found on airliners. Would be curious to see how the Aerowinx TCAS you mentioned would react.

Of course, you are free to have a try and program something, but I’m afraid this is way more complicated than that, since the decision to climb/descend is related to a high number of factors: speed of each airplanes, calculated closing point, proximity to ground or not, proximity to operational ceiling, to name a few...
Not mentioning multiple conflicting targets at the same time.
The system has to continuously monitor position and projected trajectory of conflicting traffics and make a decision accordingly, including calculating the minimum/maximum vertical speed needed to avoid the conflict.
Have a look at the FAA document about TCAS implementation I provided, it is very informative.

Jacques

[Sling]

Mode C is a dying breed these days with the ADSB mandates, but it's still not full TCAS.

[JackZ]

Mode C is definitely not a TCAS at all, what I meant is that a standard FSX/P3D G.A. aircraft is likely to be transponder mode C equipped, that is a discrete code with reporting altitude. In Europe mode C transponders have been superseded by mode S (ADSB) digital transponders for quite a few years I think.

A TCAS equipped aircraft is probably limited to Traffic advisory (TA) only, regarding conflicting mode C traffic, considering the limited quantity of informations transmitted. On the other hand one can probably get more informations from FSX/XP AI aircrafts, such as speed, heading and VS? I’ve never been on that field.

Jacques

Jacques

[flyatr]

I derived the logic from the ATR flight manual.

Key to the traffic display :
-------------------------------------
-- Open cyan diamond: altitude is greater than ±1200 feet, or distance is beyond 6 nm (No further info displayed.)
-- Intruder within 6 nm range:
-- Cyan filled diamond: aircraft is within ±1200 ft
-- Filled yellow circle: aircraft is within ±800 ft
-- Solid red square: aircraft is within ±600 ft
-- Arrow: AI aircraft is either climbing (^) or descending(v) at a rate greater than 500 ft/m.
-- Number: Altitude difference between own and intruder aircraft in ft/100 (Number 6 means difference is 600 ft.)
-- Plus (+): The intruder is above. Minus (-): The intruder is below

A red square is an aircraft that would generate a TCAS warning
A yellow circle generates an advisory.

[JackZ]

Thanks for the information.

The protection volume has a pear shaped shape with the largest part in front of the aircraft, the size of it depending on the aircraft’s speed (see page 27 of the FAA booklet on TCAS).
As it is said: “ The main concept behind TCAS is the use of Tau which is the slant range between aircraft divided by the rate of closure or range rate. This concept is based on time, rather than distance, to the closest point of approach in an encounter.”

The real problem IMHO lies with resolution advisories (RA) (red square), as the TCAS has not only to give the pilots the correct climb/descend instruction pertaining to the current situation, but has also to determine the minimum /maximum vertical speed ranges that are allowed to clear the conflict( the red/green arcs on the VSI). These vertical speed ranges are subject to change if the configuration of the threatening aircraft changes (speed, altitude, closing rate).
Aniway I’m already impressed by what you’ve achieved so far.

Jacques

[flyatr]

Yes I looked at this graphic to better understand:

[JackZ]

That’s an interesting problem.
I guess that to create the corresponding danger areas, one has to calculate the Tau factor for each target.
Tau=slant range/closing rate
Slant range is the direct distance between targets including the altitude difference, and the closing rate is I guess the sum of the “facing component” of the target’s speed (GS I think) and own’s plane GS speed. You’ll end up with a Tau time in seconds for each target, that will enter into one of the three pear shaped sectors.

Obviously the red sector is closer if an airplane is coming from the rear, since both ground speeds substract instead of adding up, so the Tau time at a given distance is much higher when closer than from the front.

If the closing plane is coming from the side, I don’t know if the facing component only has to be taken into account in the closing rate calculation, or if a composite speed vector component oriented towards the plane has to be calculated.

Jacques