TCAS warning
 

Suppose you are descending idle thurst and high rate of descent. Which aural warning would you get if for any reason there was a traffic below. Besides the TA "Traffic Traffic " Which RA would occur ? "REDUCE DESCENT" or "DESCEND, CROSSING DESCEND"
I was thinking it could be "REDUCE DESCENT"

Depends on your closure rate really, but I think TCAS 2 would most likely give an 'ADJUST VERTICAL SPEED' RA.

I haven't yet come across a REDUCE DESCENT RA on our fleet.

1. Adjust Vertical Speed, Adjust.
2. Monitor Verical Speed.
3. Clear Of Conflict.

As Gary Lager puts it, it depends on your closure rate. 3 types of RA advisory will be given:

1. Traffic advisory : "TRAFFIC"
2. Preventive RA : "MONITOR VERTICAL SPEED"
3. Corrective RA : "CLIMB", "DESCEND", "MAINTAIN VERTICAL SPEED MAINTAIN" and "ADJUST VERTICAL SPEED ADJUST".

I haven't heard of any "REDUCE DESCENT" RA.

Not exactly.

"traffic, traffic" is a TA, not an RA.

In the scenario given, monitor V/S will not be issued before adjusting, because we are the aircraft causing conflict. Monitor V/S is instruction to keep present rate, which is exactly what we must not do and TCAS will advise accordingly.

I also do not recall any "reduce descend" alerts but my manual thinks differently:uhoh:

2 out of 7 aircraft apparently have an older version of software that has "reduce climb, reduce climb" and "reduce descent, reduce descent" alerts. On later models, these are replaced by "adjust vertical speed, adjust".

FD
(the un-real)

Oh, just to pick a nit, the difference between TA and RA is not closure rate dependant. It is distance dependant. This way the system keeps you from crashing into somebody gently.

In other words, FMC Ovht: You are correct. What brings you such a question?

Ok my bad. My sentence "3 types of RA advisory" should read "3 types of TCAS advisory". Thanks FlightDetent.

I have always thought that it is closure rate because I've once or twice receive a "Traffic Traffic" TA advisory with ND showing TA intruder in an amber circle. Traffic was right below me 1000ft in RVSM airspace, but since both aircraft were maintaining level flight TA didn't resolve into RA (no closure rate). Furthermore from Airbus' FCOM 1.34.80;
-...the TCAS determines for each intruder its relative bearing, its range and closure rate and its relative altitude if available (ATC mode C or S).

So it's probably both the distance and rate of closure.

Does anyone know if TCAS2 and T2CAS is the same?

The type of TA/RA issued is really 'time-to-impact' dependant, so relative velocity (closure rate) must be taken into account as well.

Along with relative bearing, altitude, and vertical speed, of course.

There is no such RA as 'REDUCE DESCENT', but there can be an 'INCREASE DESCENT'.

'ADJUST VERTICAL SPEED' is often given in situations where the current a/c vertical speed must be reduced (either in climb or descent) - in fact, 'ADJUST VERTICAL SPEED' always means reduce V/S.

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.

I stand corrected about 'Reduce Descent's then! I must admit I didn't go to the authoritive (sp?) source, just my old company TCAS 2 briefing document, which must have been airframe-fit specific, with Airbus MSNs all later than 0806 (I think).

Not quite.

TCAS2
Traffic Collision Avoidance System (version) 2

T2CAS

Traffic (and) Terrain Collision Avoidance system

The 2 is for 2 Ts. It is a system that combines a TCAS2 and GPWS into one box and is made by ACSS. The GPWS has a predictive "forward looking" capability similar to EGPWS (which is a Honewell trademark) as well as some other clever features.

More on t2cas at ACSS

According to this TCAS software 7.0 improvement analysis, The audio warning had been abandoned with the (previous) version 6.04a, see page 15. Version 7.0 is available approximately from 2000, so there may be older hulls with not updated software. Although the Eurocontrol borchure linked at the end of my previous post, clearly states that v 6.04a is not opeartionally compatible with RVSM.

What is the correct RT phraseology to use when you have an RA MONITOR VERTICAL SPEED?
Say for example you were decending and the monitor vertical speed range was -500 to -1000 fpm. Would the RT call be "Birdseed 123 TCAS decent"?

Whats to say that you will not get a 'Monitor Vertical Speed' with a commanded reduced rod abruptly followed by a 'CLIMB, CLIMB NOW'? Especially if the conflicting traffic is passing below. RA reversals happen.

Also applies for ADJUST V/S commands that are in lieu with ATC clearance, i.e. 1000 ft level off encounters. ?

FD.