Jump to content

Sign in to follow this  
Guest Blue Ridge Dx

TCAS RA

Recommended Posts

Guest Blue Ridge Dx

Hey guys,I'm wondering if anyone else is having a problem with the TCAS RA commands in the 737-800. I noticed a discrepancy between the voice commands i receive in the sim versus those in real life. I recently had the displeasure of witnessing a corrective RA from the jumpseat of a CRJ while on descent into Burlington, VT. I tried to recreate the scenario in the sim, and was surprised by the differences. I understand that each and every encounter is different, and the commands generated, may be completely different than during another similar encounter. But...The problem i'm having is that the phraseology used by the sim was in error.The real life TCAS RA went like this:We were out of FL210 descending to 11,000. During the descent, ATC had us level at 15,000 for traffic. The controller called "...VFR traffic 11 o'clock, 6 miles, opposite direction, indicating one four thousand, type unknown." About 10 seconds later we got the TA and the TCAS called "Traffic, Traffic". None of us saw the intruder, and the TCAS showed that he was 400 feet below, and climbing into us. About 15 seconds after that, TCAS issued the RA and called "Climb, Climb!". The PF was slow to react, and after disengaging the a/p and starting a slow pull, the TCAS said "Climb, Climb NOW!", and the 'No-Fly' arc on the VSI was commanding a 3000-3500fpm ascent. As our VS increased through 1500fpm, we saw the the traffic glint in the sun at our 1130 about 2000ft away and maybe 300ft below us (It looked like a conquest). As he went under the nose and our VS was still increasing, the TCAS said "Monitor Vertical Speed". About 5 or 6 seconds later, we got the "Clear of Conflict."When i plugged in a similar scenario in the sim (confronting a climbing intruder head-on), the encounter was remarkably similar to what had happened, with only a few differences. I couldn't get the TCAS to generate a "Climb, Climb NOW!", regardless of how long i ignored the initial RA. I did, however, on several occasions receive a single "Climb!" command. As near as i know, the TCAS should always say it twice. i.e. "Climb, Climb!". The single commands were always issued after the initial double climb command. I noticed the same behavior in RA's that involved descend commands. Has anyone else noticed this?Except for that detail, the whole thing was fighteningly realistic.Best Regards,Nick LandolfiBlue Ridge DxEDIT: Amended the intruder's altitude to 14,000...oops. 0002z NL

Share this post


Link to post
Guest TrafficTraffic

"Climb, Climb NOW" is to be issued when a descend RA is reversed to a climb RA. "NOW" means reversal. If it was strengthening an already issued climb RA of "Climb, Climb", the aural should have instead been "Increase Climb, Increase Climb" and commanded +2500fpm.The only way you could get a V/S command of 3000-3500fpm is if you were already climbing that fast, in which case the aural would be "Maintain Vertical Speed, Maintain." A corrective RA cannot command greater than +/- 2500fpm. This is all straight out of the TCAS II v7 specs. I'm trying to rectify the specs with what you saw.I was just able to generate "Climb, Climb", with a slow reaction to +500fpm instead of the commanded +1500fpm and a few seconds later got "Increase Climb, Increase Climb" and command of +2500fpm. This wasn't head-on traffic, however.I've never heard a single "Climb" aural. I know that the logic cannot issue such an aural. Perhaps in some situations PMDG's code doesn't play the aural twice? Just guessing here. I use the same aurals in my 767 IVSI, and for "Climb, Climb" I play a single "Climb" waveform twice. I think PMDG is doing the same thing.Lee Hetherington, PP-ASEL (KBED)(developer of the TCAS II v7 logic used in the 800/900 upgrade)

Share this post


Link to post
Guest Blue Ridge Dx

Hey Lee,Thanks for the quick reply. Perhaps my observations are slightly in error. Admittedly, i spent a lot more time looking for the traffic, than i did at the ND, so if the climb command is limited to 2500fpm, then thats probably what i was seeing.As far as the reversal goes, we were definitely being instructed to climb the entire time. No reversal, at all. Is it possible to receive a "Climb, Climb NOW!" in level flight if you're not reacting to the initial "Climb, Climb!"? That may be the explanation, because the PF did not react to the RA for at least 10 to 12 seconds (just guessing here, but it was a looooooooong time.) Thanks,NickBlue Ridge dx

Share this post


Link to post
Guest TrafficTraffic

Hi Nick,I do not see how it is possible to get "Climb, Climb NOW" without it being a reversal. Just Google for "Climb, Climb NOW" and you'll find lists of all the aurals, and "NOW" is always a reversal, not a strengthening. What Google finds is consistent with the DO-185A document specifying TCAS II v7 behavior that I relied on. That's all I can really go on.What was the PF doing for 10-12 seconds? It is my understanding that you are to follow TCAS command within 5 seconds. Ignoring it for that long could be dangerous. TCAS takes precendence over ATC clearances.A couple months ago I was returning to KBED in a C-172. I overheard a Citation entering the area, get a traffic warning from ATC, and then shortly thereafter the Citation reported "TCAS Climb" to warn ATC they were climbing out of their cleared altitude. And no, I wasn't his traffic. ;)Lee Hetherington, PP-ASEL (KBED)PS: Maybe the CRJ's TCAS has bugs!

Share this post


Link to post
Guest Blue Ridge Dx

>What was the PF doing for 10-12 seconds? It is my understanding that >you are to follow TCAS command within 5 seconds. Ignoring it for >that long could be dangerous. TCAS takes precendence over ATC >clearances.The 64,000 dollar question! The FO asked twice if the CA was going to respond, and there was no reaction until the FO put his hands on the yoke, and pressed the A/P Disconnect to initiate the climb. There were more than a few words spoken once we were on the ground. And as for dangerous...damn skippy! We had less than 300ft vertical seperation, and nil horizontal. If we had not reacted, we (and 50 pax) WOULD be dead...it was that close. The CA said he 'thought' he had the traffic in sight, and thus delayed his reaction, finally deciding that he DIDN't have the traffic. We weren't too concerned about the clearance, and the FO did tell the controller that we were climbing in responce to an RA. The controller replied with a Pilot's Discretion descent to 11,000...Perhaps we are not using TCAS v7? If I recall correctly, the only time you need v7 is if operating in RVSM, right? Nick

Share this post


Link to post
Guest Blue Ridge Dx

Lee,I followed your advice and googled the TCAS aurals. From what i can tell, we're not using v7, as we received the "Monitor Vertical Speed" aural, instead of the "Adjust Vertical Speed, Adjust", do you agree?THe only problem is, the document I'm reading says that the logic for the "Climb, Climb Now" logic is unchanged from v6.4 and v7...I'm stumped...Regards,NickBlue Ridge Dx

Share this post


Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  
×
×
  • Create New...