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Aaron747
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TCAS Altitudes Question

Thu Jul 22, 2021 4:31 pm

So in having a basic understanding of TCAS, Mode S, and so on, my question regards TCAS operation itself. Can the altitude range be attenuated? What would be the maximum range possible for displaying non-threat aircraft? For example would it be possible to see IFR traffic on an airway in the FL200s from FL330?
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GalaxyFlyer
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Re: TCAS Altitudes Question

Thu Jul 22, 2021 7:22 pm

In NORMAL, it looks at a slice 2700’ above and below the current altitude. In ABOVE or BELOW, it expands the above or below range to 7,000’ and retains the 2,700’ in the opposite range. Select BELOW, it looks for targets 7,000’ below and 2,700’ above, for example. There’s also inhibits at very low altitudes and nearing maximum certified altitudes. I think it’s blew 1,000’ RadAlt, you can’t get an descend RA.

To your question, no at F330 only as low as F260 or as high as F400 depending an setting.
 
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Aaron747
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Re: TCAS Altitudes Question

Thu Jul 22, 2021 10:43 pm

GalaxyFlyer wrote:
In NORMAL, it looks at a slice 2700’ above and below the current altitude. In ABOVE or BELOW, it expands the above or below range to 7,000’ and retains the 2,700’ in the opposite range. Select BELOW, it looks for targets 7,000’ below and 2,700’ above, for example. There’s also inhibits at very low altitudes and nearing maximum certified altitudes. I think it’s blew 1,000’ RadAlt, you can’t get an descend RA.

To your question, no at F330 only as low as F260 or as high as F400 depending an setting.


I see, thanks GF. So the software doesn’t prioritize descent rates over climb rates, as I suspected. Exactly what I was looking for.
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GalaxyFlyer
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Re: TCAS Altitudes Question

Thu Jul 22, 2021 11:19 pm

Nope, just vertical profile of airspace, as selected. Auto Emergency Descent modes do automatically program the BELOW mode.

I only selected BELOW where we were knowingly going to have very high descent rates (>10,000 fpm) as part of a flight profile.
 
BoeingGuy
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Re: TCAS Altitudes Question

Fri Jul 23, 2021 6:58 am

GalaxyFlyer wrote:
In NORMAL, it looks at a slice 2700’ above and below the current altitude. In ABOVE or BELOW, it expands the above or below range to 7,000’ and retains the 2,700’ in the opposite range. Select BELOW, it looks for targets 7,000’ below and 2,700’ above, for example. There’s also inhibits at very low altitudes and nearing maximum certified altitudes. I think it’s blew 1,000’ RadAlt, you can’t get an descend RA.

To your question, no at F330 only as low as F260 or as high as F400 depending an setting.


On newer Boeing airplanes, ABOVE and BELOW go to +/- 9900 feet, not 7000. ABV/BLW/NORM is baseline on all 787s and 777-9s. Optional on other models, depending on what panel the customer selects. If you don’t have that, it’s always -2700 to +2700.

ABV/BLW/NORM is for Displays purposes only. It doesn’t affect any TCAS alerts.

I think that’s correct. No DESCEND RAs below 1000 feet. No INCREASE DESCENT below about 1450 feet. No RAs at all below 600 feet. If I’m remembering correctly.
 
greg85
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Re: TCAS Altitudes Question

Fri Jul 23, 2021 8:25 am

Newer Airbus models with T3CAS can also display traffic up to 9900ft above or below.
 
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zeke
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Re: TCAS Altitudes Question

Fri Jul 23, 2021 6:56 pm

Aaron747 wrote:
So in having a basic understanding of TCAS, Mode S, and so on, my question regards TCAS operation itself. Can the altitude range be attenuated? What would be the maximum range possible for displaying non-threat aircraft? For example would it be possible to see IFR traffic on an airway in the FL200s from FL330?


TCAS would not do that, however ADS-B could do that. The difference is TCAS works by calculating the bearing and distance between the aircraft, where "ADS-B in" is receiving the GPS position and altitude. Both systems use the mode S transponder.

greg85 wrote:
Newer Airbus models with T3CAS can also display traffic up to 9900ft above or below.


T3CAS is a marketing model from ACSS a Thales subsidiary, equivalent is also available from Rockwell Collins and Honeywell. The customer has a choice.
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