Non Transponding TCAS type question....

[Cartman's Twin]

Morning/Afternoon/Evening Ladys & Gents

Just returned from my hols (thank you FCA (/ThomsonFly of course) Costa Rica was fabulous - although as an aside why on earth do you only start flying there as the wet season starts??? Eh?)

As a London TMA ATCO sort sat in cattle class on the return leg (no room in the posh seats - DOH!) I had a moment of rare contemplation. After mentally debating exactly which unchartered procedure the drivers of the valiant steed would adopt in the event of an RT failure prior to TOD I had a second odd thought enter my jet-lag-laden grey matter.

One of the highest workload aircraft I've worked in my time that wasn't an actual emergency was a TMA overflight at FL90 of a non-transponding aircraft. Co-ordination was a nightmare, radar idents (an event more frequently encountered than rocking horse poo these days) and trying to remember this little silent chicane's painful progress through the stacks made an otherwise standard session a real brain buster. So I came to think (there is a point, trust me)....

If you were flying a regular airliner and your transponder failed one would presume that a conflicting aircraft, ie. one that would normally trigger a TCAS RA, would not receive an RA as it's TCAS would not detect your presence. Correct?

Would I be correct in hoping that your TCAS however would still produce an RA and that it does not rely on any input from your own transponder? (Answer's in the affirmative greatly appreciated, as it would surely be a gross oversight else)

And moving to my final point (you hope as much as me) in an event where a non transponding a/c was going to pass you by 1000ft above/below etc, would it be of any use if you were forewarned of this or would you not generally notice the sudden passing of an aircraft 'cross one's brow that had not been tracing it's earie glow on your TCAS display shortly beforehand.

As you can see, I was bored, my girlfriend was snoring and I was suffering from sleep deprivation. Please forgive verbosity, it's been 32 hours since I got up on Thursday in a bed far bigger than the example I now face.

Take care one and all

Cartman

:8

[Gulfstreamaviator]

I hope for some good answers.

I have also considered the situation, but from a drivers view point.

To answer the last question first: with out TCAC, I now feel naked. I have had intermittenat TCAS failures in last few weeks, yes, I know this is a major problem, and should be reported, but..................

You guys in ATC have no knowledge of our status as far as TCAS goes, and must assume that it is fully functional, unless S/E.

We have twin ATC, so should never be without. BUT lets assume that we have no ATC, in todays busy skies, I would be tempeted to say that we must land in the FIR that is alerted to the problem. FL90 transditting the London TMA, should be banned, and a reroute North, with Lon Mil, would be my suggestion, plus a F15, as wing man.
Or "clear to leave controlled airspace".

only a thought...glf

[WorkingHard]

"FL90 transditting the London TMA, should be banned" - Why do you say this please? Is the airspace not open to all who can legally use it?

[anotherthing]

It shouldn't be banned - however invariably the type of aircraft that flies about at those levels is very slow and quite small, often with unprofessional (in the proper sense of the word) pilots... and usually small enough to avoid paying navigation charges.

I personally believe that in some airspace, navigation charges should be inversely proportional to the aircaft size as the ATCOs workload generated is much higher dealing with these flights than with passenger jets.

These overflights get in the way of everything as they transit!

Cartmans Twin - with regards to your question about passing traffic info - my question to you would be why would you think about not passing it? If you have the time do it - it's entirely sensible and correct that you should. CAS may be a 'known traffic environment', but thats 'known' traffic to you the ATCO, not to the pilots!!

[Itswindyout]

Banned, I agree, as I assume it is "controlled" airspace, with certain levels of mandatory equipment.

If I remember correctly, acces to continued use of Controlled Air Space, with defective equipment, is at the discretion of the Air Traffic Contol Unit.

So Ban, or enforce a reroute, or descend clear of CAS.

I assume: I would not be allowed to enter CAS without a transponder, so why should I continue in congested airspace.

windy

[Carl Rawson]

I'm not entirely sure that I understand the question but my understanding of TCAS II is that it is an intercommunication system that provides 'Traffic Advisories' (TA) and ultimately 'Resolution Advisories' (RA) between 2 aircraft that are Mode C or S equipped and thus using Mode C or S. However, should there be a Mode A transponder around then the TCAS equipped aircraft will still give a TA but not give an RA. Frequently (more than once a month) I get a TA going into LGW from aircraft much lower than us over the South of England and even during the climb out from aircraft that are operating from fields below the LGW TMA. Hence SID's usually say "to be 3000' by DET 32d, 4000' by DET43d" for example.
The TCAS II RA's give instructions to "Climb", "Descend", "Increase Climb/Descend", "Monitor Vertical Speed" and "Climb Crossing Climb". Not doubt there will be more but I did my ATPL's some years ago and as they say S.I.S.O.:E Do as you're told and you can't go too far wrong. I think that I'm right in saying that this is the only time that a pilot can deviate from an assigned FL without the command of an ATCO.
It does not give lateral commands, and my understand of that is that this was for TCAS III which has been inched to the back burner.
As for ATC not knowing about the impending TCAS RA then I beg to differ. A former Capt. at my airline had a TCAS RA at his previous airline when another a/c was cleared climbing through his level and when he got the subsequent AAIB report he was surprised just how many 'bells and whistles' the ATCO's have at their disposal. Apparently the warning lights/sirens were going off well before he got his TCAS RA. Chris, I hope that I'm not misquoting you and we all hope you're doing well now.
On a completely different subject, hats off to you ATCO's. You're job sounds so stressful at times and yet you still manage to remain so chipper!
Oooh! And as for the Radio Failure. Sqwawk 7600 and follow the flight plan and STAR to the letter! Then let the finest ATC facility in the world clear the airspace for you. You are after all an a/c in distress.

[mad_jock]

I can only talk about the basic Honeywell setup.

You have 2 transponders which are selectable on the panel.

If one transponder fails and the tcas goes offline you can select the other one and it comes back online.

If both transponder's fail you won't be visable to other aircraft or ATC the TCAS will go into FAILED mode and neither TA's or RA's or for that matter targets appear on the display.

In my limited experence the failure of a transponder is the least of your worries and easiest to fix for the TCAS dropping offline.

The box of tricks has multiple data inputs from various other instruments and any fault and it drops out. And for any retrofit TCAS installation there seems to be a bit of luck involved trying to trouble shoot it.

Our MEL dispatch with TCAS U/S is 6 flights. Which can be a bit of a swine because we know that the real issue is the rad alt which is a 10 day defered defect but as its part of the data bus for TCAS and EGPWS it takes them with it and then its limited to 6 flights. But this isn't as bad as the transponder failures because other aircraft will be able to get TA''s and RA's.

So as Gulf states the whole proccess of getting a snag fixed can take weeks as the engineers try and trace whats annoying it. They have an annoying habit of working on the ground on the test kit then failing as soon as you get the gear up.

[Capt Pit Bull]

Would I be correct in hoping that your TCAS however would still produce an RA and that it does not rely on any input from your own transponder? (Answer's in the affirmative greatly appreciated, as it would surely be a gross oversight else)

Sadly you'd be wrong. The transponders and the TCAS transmitter/receiver are intimately connected. If both transponders are U/S (or at standby) the TCAS will not be working.

pb

(p.s. perhaps a mod might relocate this to a more appropriate forum)

[Cartman's Twin]

Thanks for the replies so far Folks, very useful stuff.

And PB, thanks for confirming what I feared! I may have the simple processing power of an ATCO brain but I had hoped that inputs from elsewhere within the cockpit of an a/c that had suffered a transponder failure would be sufficient to allow it's TCAS to maintain it's functionality. Sadly not!

Keep up the good work

(And if poss, I'd rather it wasn't moved. I originally added it to what may be interpreted as a 'more appropriate forum' and had no replies whatsoever. And there is certainly a serious (and hopefully useful) element to the thread)

[Cartman's Twin]

For what it's worth I'm certainly not advocating the banning of FL90 overflights within the TMA. Yes they do have a disproportionately high workload, and due to their weight are very unlikely to be paying route charges. BUT they are still a 'valued customer', they're often rerouted some way of their flight planned route to ease traffic flow and we would always have the option of saying 'no' if we're unable to accommodate.

This is very rare indeed but always possible. Or they can drop outisde CAS and trundle beneath!!

[sevenstrokeroll]

Wow...British English is so different than USA English.

One of your questions was about (I think) was about having traffic pointed out even if your TCAS wasn't working or another plane didn't have a transponder working.

I would want you to point out (transmit a traffic advisory) the traffic. We still have eyes you know.

And most airliners have two transponders, so advise us of lost transponder and we would switch to the other one. BUT, sometimes we are dispatched with one inop (this is roughly the UK equivilent of U/S...which we think means unservicable...here in the USA, US means US) and if the other one fails we are out of luck.

Our airline was the testbed for TCAS in the USA. TCAS is vital...especially with an overworked ATC system. IMHO, I wouldn't allow TCAS to be placed on MEL (this means minimum equipment list, but can also mean multi engine land...the former is the case in this post)