Transponder Mode A and TA
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Join Date: Feb 2007
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Transponder Mode A and TA
Hello guys,
Here is situatuion, VFR traffic circling in uncontrolled airspace squawking mode A only, another traffic descending with shallow rate, separation more than 1000' reports TA...question is would any transponder squawking A only would generate TA for other traffic?
Here is situatuion, VFR traffic circling in uncontrolled airspace squawking mode A only, another traffic descending with shallow rate, separation more than 1000' reports TA...question is would any transponder squawking A only would generate TA for other traffic?
Join Date: Nov 2006
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TCAS measures slant range to a mode A target, just like DME. Assuming they are not at same altitude, the rate of closure will decrease, and the target may disappear, or actually move around at the slant range distance when crossing over.
GB
GB
A TA can occur against a non-Mode C target due to the closing range as Graybeard says.
However if the true height difference is large (eg your aircraft is at FL200 and the non-Mode C is at FL50) the closing rate of lateral separation has to be pretty high, and slant-range geometry dictates that the TA will anyway tend to cancel as the lateral separation reduces. This is because the vertical separation will then predominate and the closing rate will appear to be dropping (ie the supposedly co-height threat will ultimately appear to be passing safely to the side).
However if the true height difference is large (eg your aircraft is at FL200 and the non-Mode C is at FL50) the closing rate of lateral separation has to be pretty high, and slant-range geometry dictates that the TA will anyway tend to cancel as the lateral separation reduces. This is because the vertical separation will then predominate and the closing rate will appear to be dropping (ie the supposedly co-height threat will ultimately appear to be passing safely to the side).
Last edited by Dont Hang Up; 22nd Apr 2009 at 12:21. Reason: typo