Probability of conflicting traffic?
Joined: Mar 2000
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From: U.K.
I have to agree with ShyT about TCAS, it is a fantastic tool and once you have used it, you don't really want to fly without it.
It was critical at my last company as we would often be returning to base after 9 in the morning and would usually try and get descent OCA to try and speed things up for our return, rather than being left very high until the last minute causing us to have to scream down.
When you are doing over 200kts at around 3000' OCA, then you really don't see an awful lot of traffic, TCAS was utterly invaluable for helping us pick our way back in safely. If we didn't have it fitted (tight wad company!) then we would never risk taking an early descent even if it was gin clear with two crew keeping their eyes open. (We were supposedly IFR as well.........)
It was critical at my last company as we would often be returning to base after 9 in the morning and would usually try and get descent OCA to try and speed things up for our return, rather than being left very high until the last minute causing us to have to scream down.
When you are doing over 200kts at around 3000' OCA, then you really don't see an awful lot of traffic, TCAS was utterly invaluable for helping us pick our way back in safely. If we didn't have it fitted (tight wad company!) then we would never risk taking an early descent even if it was gin clear with two crew keeping their eyes open. (We were supposedly IFR as well.........)
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Now you see, if I hadn't posted such a comment I would never have got such a detailed response 
Only ATPL level thoery here. I'm keen to know what I am wrong about though. An RA in controlled airspace must be reported, so they are taken pretty seriously. If you turn RA off, then you have a potentially more complex situation perhaps? Its fine if you are the only bod for miles using TCAS at 2500' in and around Farnborough (possibly a bad example because of the number gliders), but if everybody else (the original point) was flying about in Class G with TCAS in TA mode only, how exactly would the multitude of warnings be resolved? Just more possibility for somebody to misinterpret the screen and climb when they should be descending. Also, you said it, "commercial", you are properly trained and well practiced in its use. If we all had TCAS then would that really be the case?
I really understand if you are fast traffic, the sitaution is different, but the point IO540 was making is that we should all have TCAS, that is my point of contention.
Although the visual lookout is inefficient, I'm not sure it is neither ultimately ineffective nor inappropriate for VFR. Also, the lookout is proactive activity. I personally think that technology could lead to a more reative approach to flying. I can't see how that can be a good thing.
Only ATPL level thoery here. I'm keen to know what I am wrong about though. An RA in controlled airspace must be reported, so they are taken pretty seriously. If you turn RA off, then you have a potentially more complex situation perhaps? Its fine if you are the only bod for miles using TCAS at 2500' in and around Farnborough (possibly a bad example because of the number gliders), but if everybody else (the original point) was flying about in Class G with TCAS in TA mode only, how exactly would the multitude of warnings be resolved? Just more possibility for somebody to misinterpret the screen and climb when they should be descending. Also, you said it, "commercial", you are properly trained and well practiced in its use. If we all had TCAS then would that really be the case?I really understand if you are fast traffic, the sitaution is different, but the point IO540 was making is that we should all have TCAS, that is my point of contention.
Although the visual lookout is inefficient, I'm not sure it is neither ultimately ineffective nor inappropriate for VFR. Also, the lookout is proactive activity. I personally think that technology could lead to a more reative approach to flying. I can't see how that can be a good thing.
Last edited by High Wing Drifter; 1st December 2005 at 16:37.
Joined: Jun 2003
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From: EuroGA.org
HWD
I never said everybody should have TCAS. It's 15 grand or so, min, for the cheapest systems that give azimuth (essential).
I didn't even say everybody should have a Mode C transponder (I do actually think that).
What I have been saying is that the benefit of a lookout is illusory [hears the sound of windows at CAA Gatwick and Kingsway opening and the entire GA Dept jumping out] and that if one is after a solution it has to be TCAS, and obviously that will never work properly until Mode C is mandatory.
Luckily for most, midairs are very rare so, for the typical GA "low value payload" (you or your granny) there is very little reason for spending the money.
And even if you do spend the money, it won't pick up maybe 50% of traffic because they don't have transponders or have them switched off, intentionally or not.
Those commercial pilots here swearing blindly how wonderful TCAS is must be aware that they are missing a lot of stuff
I would bet that below say 2000ft > 50% don't transpond, especially self fly hire pilots. Higher up it will be a lot better. Most owner-pilots that go distances switch on Mode C religilously.
I wonder what will happen in 2009. What will they do about e.g. gliders and vintage planes with no electrics?
It doesn't bother me; everything in life is a risk and the sky is big and is 3D. I just don't like to bet against known odds, like joining overhead with 5 others, of which I can see just 2
I never said everybody should have TCAS. It's 15 grand or so, min, for the cheapest systems that give azimuth (essential).
I didn't even say everybody should have a Mode C transponder (I do actually think that).
What I have been saying is that the benefit of a lookout is illusory [hears the sound of windows at CAA Gatwick and Kingsway opening and the entire GA Dept jumping out] and that if one is after a solution it has to be TCAS, and obviously that will never work properly until Mode C is mandatory.
Luckily for most, midairs are very rare so, for the typical GA "low value payload" (you or your granny) there is very little reason for spending the money.
And even if you do spend the money, it won't pick up maybe 50% of traffic because they don't have transponders or have them switched off, intentionally or not.
Those commercial pilots here swearing blindly how wonderful TCAS is must be aware that they are missing a lot of stuff
I would bet that below say 2000ft > 50% don't transpond, especially self fly hire pilots. Higher up it will be a lot better. Most owner-pilots that go distances switch on Mode C religilously.
I wonder what will happen in 2009. What will they do about e.g. gliders and vintage planes with no electrics?
It doesn't bother me; everything in life is a risk and the sky is big and is 3D. I just don't like to bet against known odds, like joining overhead with 5 others, of which I can see just 2
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,116
Likes: 1,091
From: Wandering the FIR and cyberspace often at highly unsociable times
HWD,
The TCAS fit we use doesn't have the facility for the pilot to select RA, it's in permanent TA only.
Multiple TCAS conflicts are dealt with in exactly the same way as multiple visual conflicts in VFR - usually you LOOK out of the window and make a decision which avoiding action is most appropriate.
TCAS prioritises an alert on one aircraft, which may or may not be the most appropriate one, from personal experience. It may give a "false" alert if there is no mode C return. These are the frightening ones as the pilot doesn't know where to look to resolve the conflict - it could be same level, below or above him - and the azimuth may or may not be accurate - so it could be left OR right of the nose! (It might easily be up to 2700 feet above or below on our type, depending on the "airspace" setting).
I wish we could dispel the common trap of thinking that we "lucky TCAS folk" rely on it solely and fly around "heads in" because of it. We certainly don't - if anything TCAS gets a pilot's eyes OUTSIDE the window; those little white dots on the screen are a constant reminder that there are other aircraft in the vicinity!
I personally fit the TCAS instrument display into my normal lookout scan because LOOKOUT remains the primary method of collision avoidance - the ANO says so, as well as an experienced pilot's own common sense. Obviously, not all aircraft have a transponder in any event, so it would be a very unwise pilot who doesn't look out.....
As I said, TCAS isn't reliable enough in azimuth to depend on it in isolation. It IS very good in reporting altitude of other traffic, provided of course that the other traffic has a serviceable Mode C in use, so it's always best to resolve a potential conflict by altitude separation if possible.
That's why I tend to have a bee in my bonnet about permanent use of Mode C if it's fitted and paid for .... it's a potential lifesaver for both parties. If you have Mode C, please use it in the circuit too, unless ATC request otherwise because then we can "eliminate your aircraft from our enquiries". Ta.
One more point: TCAS helps a pilot to be MORE pro-active, not reactive. If you are aware of an aircraft 20 miles or more away you can obviously do something about resolving a potential conflict FAR more easily than if you are obliged to rely on lookout alone, which will result in an aircraft being "spotted" much later / closer in average conditions.
I began flying for my living in 1977 and have been doing so continuously ever since (RAF jets / Support helicopters / QHI / Heli Display pilot / Military QFI SEP / Heli SAR S.E. Asia / UK Police / VIP corporate). I've had some pretty close shaves during all that and I KNOW the limits of the human eyesight (even though I still have 6/5 vision outside the cockpit). Anything that helps me out is a bonus, as far as I'm concerned. Anyone who thinks that sole reliance on the vagaries of the human eyesight is the only good way, is sadly misguided.
The TCAS fit we use doesn't have the facility for the pilot to select RA, it's in permanent TA only.
Multiple TCAS conflicts are dealt with in exactly the same way as multiple visual conflicts in VFR - usually you LOOK out of the window and make a decision which avoiding action is most appropriate.
TCAS prioritises an alert on one aircraft, which may or may not be the most appropriate one, from personal experience. It may give a "false" alert if there is no mode C return. These are the frightening ones as the pilot doesn't know where to look to resolve the conflict - it could be same level, below or above him - and the azimuth may or may not be accurate - so it could be left OR right of the nose! (It might easily be up to 2700 feet above or below on our type, depending on the "airspace" setting).
I wish we could dispel the common trap of thinking that we "lucky TCAS folk" rely on it solely and fly around "heads in" because of it. We certainly don't - if anything TCAS gets a pilot's eyes OUTSIDE the window; those little white dots on the screen are a constant reminder that there are other aircraft in the vicinity!
I personally fit the TCAS instrument display into my normal lookout scan because LOOKOUT remains the primary method of collision avoidance - the ANO says so, as well as an experienced pilot's own common sense. Obviously, not all aircraft have a transponder in any event, so it would be a very unwise pilot who doesn't look out.....
As I said, TCAS isn't reliable enough in azimuth to depend on it in isolation. It IS very good in reporting altitude of other traffic, provided of course that the other traffic has a serviceable Mode C in use, so it's always best to resolve a potential conflict by altitude separation if possible.
That's why I tend to have a bee in my bonnet about permanent use of Mode C if it's fitted and paid for .... it's a potential lifesaver for both parties. If you have Mode C, please use it in the circuit too, unless ATC request otherwise because then we can "eliminate your aircraft from our enquiries". Ta.
One more point: TCAS helps a pilot to be MORE pro-active, not reactive. If you are aware of an aircraft 20 miles or more away you can obviously do something about resolving a potential conflict FAR more easily than if you are obliged to rely on lookout alone, which will result in an aircraft being "spotted" much later / closer in average conditions.
I began flying for my living in 1977 and have been doing so continuously ever since (RAF jets / Support helicopters / QHI / Heli Display pilot / Military QFI SEP / Heli SAR S.E. Asia / UK Police / VIP corporate). I've had some pretty close shaves during all that and I KNOW the limits of the human eyesight (even though I still have 6/5 vision outside the cockpit). Anything that helps me out is a bonus, as far as I'm concerned. Anyone who thinks that sole reliance on the vagaries of the human eyesight is the only good way, is sadly misguided.
Last edited by ShyTorque; 2nd December 2005 at 09:29.
Joined: May 2001
Posts: 4,729
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From: 75N 16E
Traffic info is excellent. You can see if you're going to be ramed up the a*se and from those places that you can't see. For example a biz jet was descending from my RH side above the wing of a 182, and I could see them coming on the traffic display but not visually . No doubt they had TCAS anyway, but assuming they hadn't and hadn't seen us.........
It is ok in the circuit, makes it easier to see where numbers 1,2 and 3 are, and it doesn't distract....
Cheers
It is ok in the circuit, makes it easier to see where numbers 1,2 and 3 are, and it doesn't distract....
Cheers
Joined: Feb 2001
Posts: 647
Likes: 0
From: UK
" . . . TCAS isn't reliable enough in azimuth to depend on it in isolation. "
Just for info - what sort of things go wrong? Does anyone know why? Will it improve with 100% Mode C/S carriage, if/when that happens including gliders etc.?
If not, what would be needed to improve TCAS to be 100% reliable, if anything could?
Chris N.
Just for info - what sort of things go wrong? Does anyone know why? Will it improve with 100% Mode C/S carriage, if/when that happens including gliders etc.?
If not, what would be needed to improve TCAS to be 100% reliable, if anything could?
Chris N.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,116
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From: Wandering the FIR and cyberspace often at highly unsociable times
There's a lot of good reading stuff on the internet about the limitations of the "see and avoid" principle. Here's a good link for a start:
http://www.atsb.gov.au/publications/...and_Avoid.aspx
The .pdf download document at the bottom of that page is very good.
http://www.atsb.gov.au/publications/...and_Avoid.aspx
The .pdf download document at the bottom of that page is very good.
Thread Starter
Joined: Feb 2001
Aviation Qualifications: PPL
Posts: 1,222
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From: Worcestershire, UK
Instead of a TCAS for GA, with all the inherent inaccuracy of azimuth, how about a GPSCAS? It surely wouldn't be very hard to develop a GPS that transmitted it's position, and received data from other GPS's for conflict calculations.
The Marine world has something similar already with the Ship Identification system, although that (at the moment) is not used directly for collision avoidance, though it does assist identification of "blips" on the radar and can help avoid the oft-heard RT transmission "ship on my port side, what is your intention?"
The Marine world has something similar already with the Ship Identification system, although that (at the moment) is not used directly for collision avoidance, though it does assist identification of "blips" on the radar and can help avoid the oft-heard RT transmission "ship on my port side, what is your intention?"
Thread Starter
Joined: Feb 2001
Aviation Qualifications: PPL
Posts: 1,222
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From: Worcestershire, UK
Currently requires a mode S tranny maybe, but surely a simple lightweight lowcost (OK that maybe unlikely) GPS transmitter/receiver/conflict detector could be developed. Given the tiny signals that GPS's receive, they presumably would not be required to belt out high power output signals unlike txp's, and accordingly, could work on batteries for non-elec aircraft.
Joined: Mar 2000
Posts: 3,130
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From: U.K.
I'll let you be the judge of that...... Do you think I want to suck all the fun out of flying?
It'd be difficult to do a an aero's sequence if I needed clearance everytime I wanted to change altitude or heading!
It'd be difficult to do a an aero's sequence if I needed clearance everytime I wanted to change altitude or heading!
Joined: Aug 2000
Posts: 3,648
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From: UK
Currently requires a mode S tranny maybe, but surely a simple lightweight lowcost (OK that maybe unlikely) GPS transmitter/receiver/conflict detector could be developed. Given the tiny signals that GPS's receive, they presumably would not be required to belt out high power output signals unlike txp's, and accordingly, could work on batteries for non-elec aircraft.
1) Use the extended squitter of Mode S (i.e. its capability of sending data along with the response to interrogation)
2) VDL Mode 4, a fairly complex system working on a couple of VHF frequencies, but allowing relatively low power systems to work. It was developed in Sweden and has been championed by Eurocontrol.
3) UAT, a system developed by MITRE specifically for ADS-B and aimed at the GA user. It uses UHF, like the transponder. It's under trial in Alaska for ADS-B.
The FAA decided (also see here) to use a combination of UAT and Mode S (called 1090ES) for ADS-B.
In Europe, since we'll almost all be required to carry Mode S transponders anyway, there's less of a pressing need for development of a low-cost low-power alternative link technology -- though of course there is a pressing need for development of a low-cost low-power Mode S transponder!