NATS Transponder Use Survey
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Traffic systems normally have a window (+/- 2500'?) outside of which they ignore anything. So if you're doing aero's with a top at 5k and an airliner goes over the top at 10k their TCAS will probably ignore you. Certainly this is the case for most TIS / TAS type systems.
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Englishal - it's not an 'attitude'! Simply what I might call "conventional wisdom" passed from those I've trained with, and for exactly the TCAS RA reasons stated by backpacker; I'm guessing the reciever has no means to know I'm not some mil-jet and have no hope of sustaining that rate of climb. Further to IO540's suggestions, it seems I'd be perfectly visible on primary radar anyway?
As per the thread, it's one reason to keep the txp off - in fact, about the only one I'm aware of; I'm even willing to be convinced it's not a good reason. Just answering the question. (and keeping my eyes out the window)
Just to add (replies crossed). As I understand it, the big tin is separated from the base by 'not less than 500ft'; I can fly right up to the base of the airspace. That means in extremis only 500ft separation - I might pull up into something at 150kts 1000ft below - that might wake up Nigel in his 747 rather abruptly! Unfortunately rather airspace constrained, and I rather like having a bit of wriggle room; it tends to prolong one's career, hence being up under the base..
And yes Rod, I can think of plenty of nefarious reasons, but that wasn't the point!
As per the thread, it's one reason to keep the txp off - in fact, about the only one I'm aware of; I'm even willing to be convinced it's not a good reason. Just answering the question. (and keeping my eyes out the window)
Just to add (replies crossed). As I understand it, the big tin is separated from the base by 'not less than 500ft'; I can fly right up to the base of the airspace. That means in extremis only 500ft separation - I might pull up into something at 150kts 1000ft below - that might wake up Nigel in his 747 rather abruptly! Unfortunately rather airspace constrained, and I rather like having a bit of wriggle room; it tends to prolong one's career, hence being up under the base..
And yes Rod, I can think of plenty of nefarious reasons, but that wasn't the point!
Last edited by Mark1234; 27th Jan 2010 at 14:48.
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Simply what I might call "conventional wisdom"
I'd be more worried about the chap in the Cirrus stuck in the same airspace as you, who will be passing through your aerobatic box in 2 minutes as he doesn't know you are there than disturbing Nigel's coffee, who will be talking to ATC anyway as George flies him to LAX....
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Further to IO540's suggestions, it seems I'd be perfectly visible on primary radar anyway?
The problem with primary-only, or Mode A only, is that there is (obviously) no altitude information.
This has various implications:
- a radar unit providing somebody with a radar service has to give out the target to everybody, because it has no idea of altitude. This is a waste of everybody's time and we already have a frequently degraded traffic service "due to controller workload".
- a radar unit in charge of a piece of CAS whose base does not extend all the way to the ground has to assume that the traffic is underneath, even when there is a direct lateral conflict with jet traffic or whatever. So far, in the UK, they have been lucky
- there are some TCAS RA issues with Mode A targets, I gather, though I don't know anything about this. I don't think TCAS totally ignores Mode A returns - does it?
- AIUI, a UK radar unit is not allowed to provide you with a radar service unless they see both primary and secondary return, so not squawking degrades things for everybody else
- not squawking makes you invisible to TCAS equipped GA planes
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This bit
Completly understand the limitations of Mode A - it seems worse than nothing at all. Normally on A+C, or just off in the special circumstance. Just to illustrate I'm not being totally perverse - consider the corner of Reading. In the right wind direction Heathrow arrivals are streaming right overhead, and the cap's at 5000.
Being pedantic, they can still look out those big clear things at the front, just like I and the very large proportion of GA does..
Serious question - how many of the GA a/c steaming around in class G are equipped to make use of my txp signal? Based on personal observation I suspect it's a vanishingly small proportion; might be higher in these parts though?
Originally Posted by IO540
Unless, following the bust, one flies back home at a pretty low level, there will be a radar track left somewhere, enough to follow if one has made a real exhibition of oneself and the motivation is there.
not squawking makes you invisible to TCAS equipped GA planes
Serious question - how many of the GA a/c steaming around in class G are equipped to make use of my txp signal? Based on personal observation I suspect it's a vanishingly small proportion; might be higher in these parts though?
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there are some TCAS RA issues with Mode A targets, I gather, though I don't know anything about this. I don't think TCAS totally ignores Mode A returns - does it?
Also TCAS has a limit of 8000ft per min so if either party is going up/down faster than that they get dropped out of the TCAS protection. Also there level disappears from the ATCO's screen I believe.
The units themselves have different display modes normal it displays traffic +- 2500ft "Above" it gives you 6000ft above 1000 below. And "below" gives you 6000ft below and 1000ft above. Gives anal retentive knobs no end of fun bitching about what you have left it set at. This setting of the display mode has absolutely no effect at all on the operation of the unit just on what you can see on your TCAS screen. If say something was above you doing 7000ft per min outside 6000ft and the box though you needed to do something it would light up your VSI with instructions and all the other good RA stuff but you wouldn't have seen it on the screen before the RA.
I am not so sure about units having to be both Secondary and primary equiped. I have been worked using secondary only and also primary only in the UK. But no doudt one of the ATC types will clarify on that point.
I will point out that the information above is for the Honeywell TCAS box of tricks I don't have a clue if other TCAS installations operate in the same manner.
Last edited by mad_jock; 27th Jan 2010 at 16:47.
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Serious question - how many of the GA a/c steaming around in class G are equipped to make use of my txp signal? Based on personal observation I suspect it's a vanishingly small proportion; might be higher in these parts though?
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.. but perhaps did not establish communication with the relevant approach controller at least 15-20nm from the field.
If you require navigational assistance, ATC should be there to help and provide vectors, workload permitting, but this should not relieve pilots of a responsibility to navigate.
If you require navigational assistance, ATC should be there to help and provide vectors, workload permitting, but this should not relieve pilots of a responsibility to navigate.
Having been nearly wiped out last year in your area, perhaps you could define what you mean here.
Take, for example an aircraft moving from Henley to Elstree. At what point does an Elstree-bound aircraft leave Wycombe and a Stapleford departure leaving to the west tune into Elstree (if at all).
So who gives vectors? Certainly not Wycombe, Elstree or Stapleford, yet a high proportion of traffic will be speaking to them.
My near miss was whilst positioning to the Elstree 26 Approach, squawking Mode C and the opposite direction traffic was head down watching TV - didn't even notice my rude gestures!!
Squawking only makes sense if someone does something with the info. At the moment there are a lot of lazy scroats who don't look out, thinking that they are fully protected when they are not
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My flying partner and I were flying near Luton airspace in November and inadvertently set the wrong altimeter reading which neither of us spotted. We were about 400 feet too high and in their airspace.
We were squawing 0013 and listening out and were clear of their CAS when the controller asked 'the aircraft in the vicinity of Bovingdon to identify themselves'.
We did this and were advised of our mistake. We apologised, were told not to worry and carried on. This shows the advantage of using the squawk properly and if a genuine mistake is made the controller is a help, not a prosecuting hindrance.
We were squawing 0013 and listening out and were clear of their CAS when the controller asked 'the aircraft in the vicinity of Bovingdon to identify themselves'.
We did this and were advised of our mistake. We apologised, were told not to worry and carried on. This shows the advantage of using the squawk properly and if a genuine mistake is made the controller is a help, not a prosecuting hindrance.
