TCAS in an Emergency Descent

[ISaidRightTurns]

Here is a question for you guys. Today I had a NWA DC9 lose pressurization over IRQ (Colliers) at FL340. The first sign I get of it is him telling me. There is traffic all over because it was fairly early and that line of TS was just to the east of ATL.
So here this guy is at FL340 SB over IRQ heading to AMG (Alma). There is traffic everywhere, including head on at 330. I start turning everyone out the way, coordinate and start getting lower a/c outta the way and giving traffic calls (most were IMC anyway).
During all this, I don't get a mode C read out. If you descend too fast, the computer thinks it's innaccurate, and doesn't display it. My question is this, would the other a/c get an RA?
BTW - He got down to 12k, got situated and continued on his way climbing back to FL220. I dunno what happened after he left our airspace.

 

[avbug]

TCAS should pick him up. It shouldn't discriminate out vertical traffic like that, as it's not part of the logic. However, last week I repeatedly had traffic in the mid thirties passing me visually that never appeared on TCAS.

Aircraft squawking don't always appear on TCAS...I stated that a week or so ago here on another thread, and folks tried to say it isn't so...it is so. Traffic doesn't always appear, and folks sometimes become a little too complacent.

I'm sick to death of hearing folks respond to traffic alerts by saying "we got him on TCAS." Nobody cares. Got him visually? No? Then you haven't "got" him at all.

 

[80/20]

I am miss more FAA guidance on this. When training foreing crew we see that they are used to more detailed procedures because some foreign AIMs (AIPs) have detailed instructions. Example extracts from European AIM (AIP):

• Initiate a turn away from route/track
• Advice ATC
• Squawk 7700
• Turn on exterior lights
• Watch for conflicting traffic both visually and by ACAS (TCAS)

 

[80/20]

I'm sick to death of hearing folks respond to traffic alerts by saying "we got him on TCAS." Nobody cares. Got him visually? No? Then you haven't "got" him at all.

Yes - I agree 100% avbug

 

[ifleyelearz]

Yes - I agree 100% avbug

I agree as well. I'm a military aviator and we were just told via an FCIF not to say the phrase "Got 'em on TCAS" when we received a traffic call. My personal pet peeve..."Got 'em on the fish finder". Last time I checked, it didn't find fish...

 

[ISaidRightTurns]

I guess my question pertains more to refresh rate. This guy went from 34k to 12k in probably less than 2 minutes. Thats 2k feet every 10 seconds (which our radar updates at). Even if TCAS refreshed twice as often as ours, and we presume saw him, it wouldn't even recognize it as traffic until about 5 seconds before we blows by your altitude.

 

[Mr. Irrelevant]

or "yeah, we're lookin". Looking at what? The hot stew? I always understood "traffic in sight" or "negative contact". Just a pet peeve. Not a big deal I suppose.

Mr. I.

 

[slowto250]

No question that TCAS will occasionally miss other A/C. Regarding the original post, I have my doubts whether TCAS would give sufficient warning to targets of potential conflict when decent rates approach or exceed 10,000 fpm, as was likely the case here.

 

[mar]

I'm no engineer, but...

I guess my question pertains more to refresh rate. This guy went from 34k to 12k in probably less than 2 minutes. Thats 2k feet every 10 seconds (which our radar updates at). Even if TCAS refreshed twice as often as ours, and we presume saw him, it wouldn't even recognize it as traffic until about 5 seconds before we blows by your altitude.

...I think the data sent between two TCAS units is exchanged pretty much at the speed of light.

Sort of like DME, which is basically a transponder.

Throw in a *little* delay for the processor and we pretty much have real time info on the display. That is to say, you can watch a plane manuever in the pattern on your display.

But I have to admit I've never observed a descent like the one you described on my TCAS.

I remember hearing about the Dallas Bump where AA MD80 were climbing to their initial altitudes on the order of something like 3-4000 fpm. And even though they were leveling they'd set off the TCAS of overflying aircraft....

...but I digress. I realize you're talking about much higher descent rates. I just wanted to chime in.

I can't stand, "Got 'im on TCAS" either.

 

[Kingairrick]

TCAS generates RAs based on the concept of "theta." Theta being the mathematical equation that takes into account time, distance, and rate of closure. It computes the theta to a CPA (Closest Point of Approach,) and issues a TA or RA based upon this calculation. I think (emphasis on THINK) that TCAS should be able to keep up with the high decent rates mentioned above. I'm interested to hear other replies...
BTW, that fishfinder thing is DORKY!!!! Just say NO!!