No problemo. All I wanted is to make sure that nobody gets the false idea that there is a minimum closure speed that triggers RA, i.e. when approaching slowly you woud be unprotected. You are.
TCAS figures out point in space/time called Closest Approach Point which is self explanatory. If the separation distance at CPA is less than preset thresholds, traffic is a threat. Now, time to CPA is calculated. TA is triggered at 48 sec to CPA, RA at 35 sec to CPA, these limits apply in upper altitudes.
In case you have slowly converging traffic, even if CPA is still way ahaed but you might get too close for comfort laterally. TCAS would prevent, there is a distance threshold, my memory fails me but figures of 1,1 (RA) and 1,3 (TA) NM loom behind.
Similar situation may happen vertically, so again there are threshold values of 850 and 700 ft respectively. I also seem to remember that target miss distance for RA is about 600 ft.
The system response is de facto independent of closure rate, no matter how fast or slow you approach, once a threshold is crossed, alert would be given. Closure rate is essential to figure out CPA and time to impact in fist place.
The nusiance warning Chrome describes sound very much like he had an aircraft fitted with TCAS II software v6.04 which is a pre-RVSM standard. I notice that the thresholds described above are set to about one half of minimum normal separation. Similarily, software 6.04 altitude threshold for TA was 1200 (or 1400) feet if aircraft was above FL 300 (the old 2000 ft level stratification zone) so you would have continious TA warning but no RA (limit 900 ft). With introduction of RVSM this would trigger unacceptable heap of nuisance warnings degrading the effectivity of the system and undermining pilot's trust. Today TCAS II software standard is version 7 that is designed within RVSM limits.
T2CAS is different system from TCAS II although I think it provides TCAS II functions.
I assure you that A321 MSN 0674 and 0684 do have REDUCE CLIMB and REDUCE DESCENT alerts and judging from FMC's post they are hardly not the last ones out there. I suppose it is a older version of something because newer aircraft have these changed to "ADJUST VERTICAL SPEED, ADJUST" with the exact meaning as you describe. Frankly, until today I never heard of REDUCE CLIMB/DESCENT aurals.
Can somebody figure out, when did this aural warining got changed? I would like to make sure that it is not a proof of 6.04 software.
FD.
Oh, the
link.