Mid air over Hertfordshire
Is it normal for the Hertfordshire Police to investigate aviation accidents, even if off-duty police officers were involved? Should this not be left to the AAIB?
I don't doubt that this is a very troubling incident for the force, and you have my sympathy, as well, I imagine, as everyone else's on the list. But surely that's all the more reason to leave the investigation to those with experience of air accident investigation, isn't it?
I don't doubt that this is a very troubling incident for the force, and you have my sympathy, as well, I imagine, as everyone else's on the list. But surely that's all the more reason to leave the investigation to those with experience of air accident investigation, isn't it?
TonyR - it happens to me at LEAST once a month. Three times in a week very recently.
It can be very unnerving when at say 7,000ft under a FIS at 250kts weighing 52tons to receive this franticly imparted information. When given the phrase 'avoiding action' then thats what you get from me.
I am not lying or exageratiing. I get this regularly as do thousands of other pilots. A suddenly appearing ModeA transpoder is presumed to occupy all levels from one to ten thousand feet and it scares us regularly. Scare us. Note that.
The closure rates and likelihood of seeing and avoiding at 250kts+ offer no comfort whatsoever.
ModeS now.
WWW
It can be very unnerving when at say 7,000ft under a FIS at 250kts weighing 52tons to receive this franticly imparted information. When given the phrase 'avoiding action' then thats what you get from me.
I am not lying or exageratiing. I get this regularly as do thousands of other pilots. A suddenly appearing ModeA transpoder is presumed to occupy all levels from one to ten thousand feet and it scares us regularly. Scare us. Note that.
The closure rates and likelihood of seeing and avoiding at 250kts+ offer no comfort whatsoever.
ModeS now.
WWW
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WWW, last night's sheep must really have got to you mustn't it? If you fly as well as you spell I'm glad I'm not down the back. You can put as many boxes as you like in GA, micros , helis and balloons but if the driver doesn't switch them on then it won't do anybody any good. Mark One eyeball is the answer but if you insist on Mode S transponders, perhaps you'll be kind enough to post your address then we can all send you the £3000 bill for fitting them.
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ozplane
Mk1 eyeball is only marginally better at spotting genuinely collission-course traffic at 100kt than it is at 250kt.
Like it or not, TAS/TCAS or whatever one calls it IS the only sure solution. And yes it does require mandatory Mode C. I bet that if Mode C was made mandatory say 10 years ago the fuss would have died out by now, there would be loads of used Mode C units to choose from for those who have less to spend, and there would be a lot less pressure on GA to go for Mode S, which currently goes for £3k+VAT from either Garmin or Honeywell.
And yes it does require people to leave their transponder switched ON, but I think any pilot with enough braincells to pass the PPL exams does know how to switch on a transponder. So those that routinely don't switch it on must be doing it for a reason. It could be training, or the desire to avoid persecution in case of horizontal or vertical airspace busts. The latter reason takes us back to training of course; novice PPL holders should not be expected to be able to navigate accurately in today's airspace using the WW1 methods taught in the PPL. In the end, training has to be the answer because nobody can stop the pilot pulling the transponder circuit breaker and, should it be subsequently investigated, claiming he didn't touch it.
The only counter argument is the statistical reality that mid-airs are very rare. But evidently this won't stop the powers to be from looking for a rather more rigorous solution, which is what's happening.
Now, if the CAA was at all smart, they would have got somebody to develop a low cost transponder, approved it immediately and marketed it. Up Yours to Garmin and the other avionics rip-off merchants; the manufacturing cost of an XP is about 300 quid.
The FAA was smart; they spent some money (vastly more money than the CAA would spend doing the above) on providing traffic info to those pilots who bought a Mode S transponder. You just need a multifunction display. That is a huge incentive because an active traffic detection system currently costs £20k+
Mk1 eyeball is only marginally better at spotting genuinely collission-course traffic at 100kt than it is at 250kt.
Like it or not, TAS/TCAS or whatever one calls it IS the only sure solution. And yes it does require mandatory Mode C. I bet that if Mode C was made mandatory say 10 years ago the fuss would have died out by now, there would be loads of used Mode C units to choose from for those who have less to spend, and there would be a lot less pressure on GA to go for Mode S, which currently goes for £3k+VAT from either Garmin or Honeywell.
And yes it does require people to leave their transponder switched ON, but I think any pilot with enough braincells to pass the PPL exams does know how to switch on a transponder. So those that routinely don't switch it on must be doing it for a reason. It could be training, or the desire to avoid persecution in case of horizontal or vertical airspace busts. The latter reason takes us back to training of course; novice PPL holders should not be expected to be able to navigate accurately in today's airspace using the WW1 methods taught in the PPL. In the end, training has to be the answer because nobody can stop the pilot pulling the transponder circuit breaker and, should it be subsequently investigated, claiming he didn't touch it.
The only counter argument is the statistical reality that mid-airs are very rare. But evidently this won't stop the powers to be from looking for a rather more rigorous solution, which is what's happening.
Now, if the CAA was at all smart, they would have got somebody to develop a low cost transponder, approved it immediately and marketed it. Up Yours to Garmin and the other avionics rip-off merchants; the manufacturing cost of an XP is about 300 quid.
The FAA was smart; they spent some money (vastly more money than the CAA would spend doing the above) on providing traffic info to those pilots who bought a Mode S transponder. You just need a multifunction display. That is a huge incentive because an active traffic detection system currently costs £20k+
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After flying through the LA special flight rules area numerous times without talking to ATC, it works well being able to make blind calls, and hear other peoples calls. The only stipulation there is that you sqwark 1201 which lets ATC know your intentions, and that you're not simply lost and bimbling into LA Class B willy nilly.
It'd work well in this country as well, there would be no cost to ATC, they could see on their radar screens that the target is sqwarking 7001 and they know that they'll be at a certain altitude even if they only have Mode A.
Until a GA friendly TCAS unit arrives for a reasonable price, and becomes mandatory, it'd be one cheap, useful way to avoid collisions in certain busy parts of G airspace. You never know, they could even open up more VFR corridors through airspace using this system.......
EA
It'd work well in this country as well, there would be no cost to ATC, they could see on their radar screens that the target is sqwarking 7001 and they know that they'll be at a certain altitude even if they only have Mode A.
Until a GA friendly TCAS unit arrives for a reasonable price, and becomes mandatory, it'd be one cheap, useful way to avoid collisions in certain busy parts of G airspace. You never know, they could even open up more VFR corridors through airspace using this system.......
EA
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I agree fully about the need for Mode C to be used wherever possible, however in the two years I've been flying I've lost count of the number of club aircraft that bear the sticker "No altitude information" on the TXP. This is a large part of the problem as I suspect many club aircraft may be in a similar state...
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For those of you you are flying machines able to use TCAS and all the other gadgetaty.
Where do you think PFA types and gliders are going to get the power required for radio, nav aids etc and then to add Mode S and TCAS?
If you have ever been in gliders cross-country you are always looking out, mainly to see if the next thermal has a glider that is doing better than you.
Please please don't assume that technology will keep you safe. We are pilots working in a risky environment. You may have all the gadgets in the world, but the one who hits you may not.
I'd like to know is there an arc of coverage for TCAS, or does it take in above and below or from the 4 o clock/8 o clock positions?
Where do you think PFA types and gliders are going to get the power required for radio, nav aids etc and then to add Mode S and TCAS?
If you have ever been in gliders cross-country you are always looking out, mainly to see if the next thermal has a glider that is doing better than you.
Please please don't assume that technology will keep you safe. We are pilots working in a risky environment. You may have all the gadgets in the world, but the one who hits you may not.
I'd like to know is there an arc of coverage for TCAS, or does it take in above and below or from the 4 o clock/8 o clock positions?
Where do you think PFA types and gliders are going to get the power required for radio, nav aids etc and then to add Mode S and TCAS?
Dynamo? Dumb? Well shall we do the math? Say we've got a 500 kg glider with a 1:40 glide ratio chugging along at 20 m/s. That's a drag of 125 N, which means that you're burning 2500 W just to stay in the air. Is 25 W from a ram air turbine for a transponder really too much to ask to keep us all a bit safer?
It is? I know some cyclists who feel the same way...
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On a slightly different note, I would like to know why for instance the Heathrow zone is as big as it is and the ceiling around it is 2500 feet. Sitting here now, I see traffic departing Heathrow turning over Burnham and all upwards of 5000ft and climbing. I would suggest to the powers that be, have a look at the reasons for having these limits, after all the aircraft now using our major airport are able to climb to altidude much quicker than before. Come on CAA what about a bit of lateral thinking and do us all a favour.
Mike
Mike
Bookworm,
Go check the peak power requirements of a transponder, then come back here and remind us just how much peak current they need, eh?
Just to save you checking, most transmit around 200W peak. Tx efficiency is low, around 30 or 40% at best, so peak power into the transponder is around 500W or so. Mean power is certainly much lower, but to supply the peaks needed you will need a pretty hefty battery. Gliders, microlights etc would find it difficult to fit a battery, in fact some microlights would probably go over the legal empty weight limit if so fitted, and end up grounded.
Finally, I don't really want a couple of hundred watts of microwave energy emanating from a small antenna a few inches under my bum, with no effective RF screening from a non-metallic structure.
Go check the peak power requirements of a transponder, then come back here and remind us just how much peak current they need, eh?
Just to save you checking, most transmit around 200W peak. Tx efficiency is low, around 30 or 40% at best, so peak power into the transponder is around 500W or so. Mean power is certainly much lower, but to supply the peaks needed you will need a pretty hefty battery. Gliders, microlights etc would find it difficult to fit a battery, in fact some microlights would probably go over the legal empty weight limit if so fitted, and end up grounded.
Finally, I don't really want a couple of hundred watts of microwave energy emanating from a small antenna a few inches under my bum, with no effective RF screening from a non-metallic structure.
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Map5623
Yes - a majority of traffic DOES make 5000 feet+ (I have seen a BA319 make FL90 during at BUR when the wind was 270-35kts!)
However, NOT all traffic does. The minimum climbout gradient is 243ft/nm for LHR SID's. Pilots MUST advise if they are unable to make it. ANZ1 and a few others (esp the older A340's) just make it - but anyone who flies around OCK on a hot summers day will see loads of slow climbing heavies going over the top at 3000ft ish struggling to stay in controlled airspace. (and loads of PPL's showing 2600 on the Mode C not talking). Not sure I would want a TCAS climb when the stick is alrady back against my chest.
As for the zone size - Yes it may appear big. but then look at the inbound approach profile. Also - we get aircraft clipping it by one mile CONSTANTLY. This would be even more sporty if the zone was brought in more.
It is there to protect the IFR traffic. Simple.
Yes - a majority of traffic DOES make 5000 feet+ (I have seen a BA319 make FL90 during at BUR when the wind was 270-35kts!)
However, NOT all traffic does. The minimum climbout gradient is 243ft/nm for LHR SID's. Pilots MUST advise if they are unable to make it. ANZ1 and a few others (esp the older A340's) just make it - but anyone who flies around OCK on a hot summers day will see loads of slow climbing heavies going over the top at 3000ft ish struggling to stay in controlled airspace. (and loads of PPL's showing 2600 on the Mode C not talking). Not sure I would want a TCAS climb when the stick is alrady back against my chest.
As for the zone size - Yes it may appear big. but then look at the inbound approach profile. Also - we get aircraft clipping it by one mile CONSTANTLY. This would be even more sporty if the zone was brought in more.
It is there to protect the IFR traffic. Simple.
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www,
not sure why you would demand Mode S, mandatory Mode C for GA traffic flying below "positively controlled" airspace would work very well for your requirements in a busy TMA. Thats how they do it in other countries with lots more traffic than the UK sees. See FARs for mandatory Mode C use and you will get an idea.
Forgive me for asking stupid questions, but why are you moving a jet around when you get a mode A target? Plenty of very authoritative posters suggest you should only do so when you get an RA. I thought TCAS RA only tell you to climb or descend, how can you do that when you don't know the altitude of the intruder? I thought TCAS is poor at determining bearing, why would you turn, surely you might hit the target? What about other traffic around, don't you think you should be concerned about separation?
not sure why you would demand Mode S, mandatory Mode C for GA traffic flying below "positively controlled" airspace would work very well for your requirements in a busy TMA. Thats how they do it in other countries with lots more traffic than the UK sees. See FARs for mandatory Mode C use and you will get an idea.
Forgive me for asking stupid questions, but why are you moving a jet around when you get a mode A target? Plenty of very authoritative posters suggest you should only do so when you get an RA. I thought TCAS RA only tell you to climb or descend, how can you do that when you don't know the altitude of the intruder? I thought TCAS is poor at determining bearing, why would you turn, surely you might hit the target? What about other traffic around, don't you think you should be concerned about separation?
Go check the peak power requirements of a transponder, then come back here and remind us just how much peak current they need, eh?
Just to save you checking, most transmit around 200W peak. Tx efficiency is low, around 30 or 40% at best, so peak power into the transponder is around 500W or so. Mean power is certainly much lower, but to supply the peaks needed you will need a pretty hefty battery. Gliders, microlights etc would find it difficult to fit a battery, in fact some microlights would probably go over the legal empty weight limit if so fitted, and end up grounded.
Just to save you checking, most transmit around 200W peak. Tx efficiency is low, around 30 or 40% at best, so peak power into the transponder is around 500W or so. Mean power is certainly much lower, but to supply the peaks needed you will need a pretty hefty battery. Gliders, microlights etc would find it difficult to fit a battery, in fact some microlights would probably go over the legal empty weight limit if so fitted, and end up grounded.
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slim_shag and WWW
Forgive me for butting in here, I am sure that WWW can answer for himself, but I have got some spare time!
It is important to distinguish between a TCAS RA, which as slim_shag correctly states should be responded to in a vertical plane and avoiding action given by ATC against a mode A target.
Under a RAS (WWW obviously operates to airfields which involve flying outside CAS and most companies require crews to get the best service they can from ATC), ATC are trying to provide 5nm from mode A returns and 3000'/5nms from unvarified mode C returns. (ref MATS 1 1.4.1 e). If separation falls to less than this, then avoiding action results. Now, if everyone used mode C, the 3000' part of this separation could be used and it may become easier for standard separation to be maintained under a RAS.
As it happens, "TRAFFIC TRAFFIC" is called by the TCAS against mode A only traffic regularly. It is worrying enough at FL80 at LAM, it must be scary as hell in IMC in class G airspace. If the offending traffic had mode C, the warning may not occur and besides WWW would have more information available to enhance his situational awareness.
Just some thoughts. I haven't decided how I feel about mandatory mode C, but then I fly mainly inside CAS these days.
G W-H
Forgive me for butting in here, I am sure that WWW can answer for himself, but I have got some spare time!
It is important to distinguish between a TCAS RA, which as slim_shag correctly states should be responded to in a vertical plane and avoiding action given by ATC against a mode A target.
Under a RAS (WWW obviously operates to airfields which involve flying outside CAS and most companies require crews to get the best service they can from ATC), ATC are trying to provide 5nm from mode A returns and 3000'/5nms from unvarified mode C returns. (ref MATS 1 1.4.1 e). If separation falls to less than this, then avoiding action results. Now, if everyone used mode C, the 3000' part of this separation could be used and it may become easier for standard separation to be maintained under a RAS.
As it happens, "TRAFFIC TRAFFIC" is called by the TCAS against mode A only traffic regularly. It is worrying enough at FL80 at LAM, it must be scary as hell in IMC in class G airspace. If the offending traffic had mode C, the warning may not occur and besides WWW would have more information available to enhance his situational awareness.
Just some thoughts. I haven't decided how I feel about mandatory mode C, but then I fly mainly inside CAS these days.
G W-H
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AlanM, I accept what you say, the point I am trying to make is that the zone is one size fits all approach. For example how about modifying the SID so traffic that cannot make the height gain must climb straight out intill at the required height. I think some of the problem is that airlines/business/money think they own the sky and everything should be done to make life easy for them. Whilst I agree we need safety, I cannot see why the Heatrow zone could be made a bit narrower. Improving the lot of traffic stuck between Heathrow, Gatwick, Luton and Stanstead.
Mike
Mike
Bookworm : "Do you not think that the fact that most transponders are fitted with 4 or 5 amp circuit breakers means that Mr Honeywell has worked out how to smooth out these peaks within the transponder unit itself?"
Have you looked at the response time of a circuit breaker?
A typical GA circuit breaker trips after about 200 to 300mS if you are lucky (some of the older ones are actually slower than this), which is shorter than the transmit pulse length. The net result is that the circuit breakers are rated at the mean current draw, rather than the peak. It is still perfectly possible to draw many times the circuit breaker rating for short pulses, which is pretty much exactly what a transponder does.
You only need to take a look at the current pulse profile on the feed to a transponder to see these high peak current pulses. It's one of the reasons that the darned things can introduce interference into comm systems if not wired into a low impedance source supply, hence the need for the battery.
Have you looked at the response time of a circuit breaker?
A typical GA circuit breaker trips after about 200 to 300mS if you are lucky (some of the older ones are actually slower than this), which is shorter than the transmit pulse length. The net result is that the circuit breakers are rated at the mean current draw, rather than the peak. It is still perfectly possible to draw many times the circuit breaker rating for short pulses, which is pretty much exactly what a transponder does.
You only need to take a look at the current pulse profile on the feed to a transponder to see these high peak current pulses. It's one of the reasons that the darned things can introduce interference into comm systems if not wired into a low impedance source supply, hence the need for the battery.
PPruNaholic!
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Bookworm, VP959: As a former avionics engineer I find your debate of interest.
Power consumption specs for GA transponders are readily available online, e.g. http://www.garmin.com/products/gtx320a/spec.html which indicates
(There is also a wirding diagram on page 31 of the install manual here http://www.garmin.com/manuals/168_In...tionManual.pdf but it just shows a connection to "aircraft power" and so does not explicitly confirm or deny the need for a battery.)
However, although they don't say it explicily in this summary spec, I would be surprised if a battery was not required in addition to a dynamo because (I am guessing) the dynamo output might not be steady, depending on flight conditions, airspeed, turns etc. and the transponder unit's design probably assumes a steady rail voltage so it may be that fluctuations, which would be smoothed by a battery if fitted, would cause grief for the transponder. We'd need more info on the dynamo specs to be sure.
Andy
Power consumption specs for GA transponders are readily available online, e.g. http://www.garmin.com/products/gtx320a/spec.html which indicates
Power Requirements: 11.0 to 33.0 VDC
Max Power Input: 12 watts @500 prf
Max Power Input: 12 watts @500 prf
However, although they don't say it explicily in this summary spec, I would be surprised if a battery was not required in addition to a dynamo because (I am guessing) the dynamo output might not be steady, depending on flight conditions, airspeed, turns etc. and the transponder unit's design probably assumes a steady rail voltage so it may be that fluctuations, which would be smoothed by a battery if fitted, would cause grief for the transponder. We'd need more info on the dynamo specs to be sure.
Andy
Last edited by Aussie Andy; 10th Jul 2004 at 13:21.
Spot on AA. The current draw quoted (around 1 amp from 12V) is the mean current. The battery is needed to cope with the high current pulses without causing the supply voltage to droop below the lower voltage limit when the thing is interrogated (or ident is pressed).
Either way, until low tx power transponders can be proven to work effectively, and become available at a reasonable price , then they really aren't practical for those who fly sub £5k aeroplanes with no electrical system.
QinetiQ Ltd were trialling a low power portable transponder a year or so ago and I heven't heard much about it since. I heard somewhere that one of the problems they encountered was that to work effectively and reliably ground SSRs would need upgrading. Presumably this was to cope with the lower tx power such a device could put out.
I suppose this discussion should really be about whether we want the open FIR to become either controlled airspace, or whether in addition to transponders we want all flying machines to be equipped with TCAS as well. Even this isn't foolproof, as it would rely on 100% illumination of all airspace by a primary radar, in order to trigger all the transponders in the first place.
Someone invented a rather neat strobe detector a while ago. As I recall it was just a cheap and fairly simple box with some photo sensors, plus some clever discriminator circuitry to detect strobe flashes much more effectively than the human eye. I wonder what happened to it?
Either way, until low tx power transponders can be proven to work effectively, and become available at a reasonable price , then they really aren't practical for those who fly sub £5k aeroplanes with no electrical system.
QinetiQ Ltd were trialling a low power portable transponder a year or so ago and I heven't heard much about it since. I heard somewhere that one of the problems they encountered was that to work effectively and reliably ground SSRs would need upgrading. Presumably this was to cope with the lower tx power such a device could put out.
I suppose this discussion should really be about whether we want the open FIR to become either controlled airspace, or whether in addition to transponders we want all flying machines to be equipped with TCAS as well. Even this isn't foolproof, as it would rely on 100% illumination of all airspace by a primary radar, in order to trigger all the transponders in the first place.
Someone invented a rather neat strobe detector a while ago. As I recall it was just a cheap and fairly simple box with some photo sensors, plus some clever discriminator circuitry to detect strobe flashes much more effectively than the human eye. I wonder what happened to it?
Giles has explained my situation precisely.
What - out of these two options - do you want?
a) An airliner of some description has a mid air with a GA aircraft. Media outrage. Knee jerk reaction - no GA aircraft allowed to fly without TCAS + a massive overnight extension of Class A + a horrendous jaw dropping increase in GA insurance premiums as you just downed an aircraft insured for £750,000,000 as my works transport usually is.
b) A £9,000 per aircraft phased introduction of a bang up to date technology that means you know precisely about 99% of the traffic 99% of the time and reduces the numbers of PPLs killed every year and totally avoids a)
Vote now, get it right and GA may have a future.
Cheers
WWW
What - out of these two options - do you want?
a) An airliner of some description has a mid air with a GA aircraft. Media outrage. Knee jerk reaction - no GA aircraft allowed to fly without TCAS + a massive overnight extension of Class A + a horrendous jaw dropping increase in GA insurance premiums as you just downed an aircraft insured for £750,000,000 as my works transport usually is.
b) A £9,000 per aircraft phased introduction of a bang up to date technology that means you know precisely about 99% of the traffic 99% of the time and reduces the numbers of PPLs killed every year and totally avoids a)
Vote now, get it right and GA may have a future.
Cheers
WWW