GPS fails over Shawbury
Carbonfibre-based lifeform
Join Date: Mar 2002
Location: London
Posts: 747
Likes: 0
Received 0 Likes
on
0 Posts
Reichman,
I wasn't actually expressing any particular attitude to navigation. The 
symbol in my post indicates that it is not intended to be taken seriously - just like the one in yours!
I find your attitude to navigation incredible. Are you advocating that GPS navigation should take precedence over map reading skills? I do hope not.
symbol in my post indicates that it is not intended to be taken seriously - just like the one in yours!
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
DW
Fair point, but I did say "in a particular spot". There is a good theoretical basis for high harmonics of certain navaid frequencies interfering with GPS. However, I have never met anyone, and have never met anyone who has ever met anyone, who can just go up in their plane that is fitted with any current-model GPS and reproduce this.
In any event, all this is an excellent reason for having a roof mounted GPS aerial. It's all down to the signal to noise ratio; if a GPS with an integral aerial is only just managing, it won't take much to push it over the edge. The total cost of a proper rooftop aerial should be about £400 incl installation, coming out on a BNC socket.
Reichman
"How did we all navigate around the world before GPS?"
The answer is that, like today, often they didn't. Even post-WW2, airliners used to get lost through gross nav errors.
I have often asked your sort of question to various old hands in sailing and flying. How did the seafarers of centuries ago manage to find Easter Island, for example, and do so at will? If you assume the horizon from say FL100, it is certain that nobody, not even a robot on a windless day, could fly a heading for that distance and end up there. These people were extremely good with the sextant and their tables. The sailors had a table on which to spread their chart and al the time in the world. The early airliners also had a full time pilot or two, a full time engine/fuel manager, and a full time navigator. They also had NDBs and even an NDB is vastly better than dead reckoning.
The trick, as far as I can tell, is that the early navigators (and this includes post-WW2 airliners) had continuous guidance along their track. Even a sextant gives you a line of latitude and is vastly better than dead reckoning and post-WW2 there were NDBs everywhere of interest which are better still. A GPS, like VOR/DME, gives you continuous guidance along a track.
Flyers that did solo transatlantic flights would have tried to use a sextant but in any case would have aimed for an easier target, e.g. the east coast of the USA, or Ireland if coming this way. You've got to do a wind corrected heading to within 5-10 degrees and you will be fine.
The difficulty, which a GPS handles very well, is that today's PPLs get barely enough training to take off, fly an easy XC flight on a perfect day, and land, yet they are expected to fly precise tracks between bits of controlled airspace.
Fair point, but I did say "in a particular spot". There is a good theoretical basis for high harmonics of certain navaid frequencies interfering with GPS. However, I have never met anyone, and have never met anyone who has ever met anyone, who can just go up in their plane that is fitted with any current-model GPS and reproduce this.
In any event, all this is an excellent reason for having a roof mounted GPS aerial. It's all down to the signal to noise ratio; if a GPS with an integral aerial is only just managing, it won't take much to push it over the edge. The total cost of a proper rooftop aerial should be about £400 incl installation, coming out on a BNC socket.
Reichman
"How did we all navigate around the world before GPS?"
The answer is that, like today, often they didn't. Even post-WW2, airliners used to get lost through gross nav errors.
I have often asked your sort of question to various old hands in sailing and flying. How did the seafarers of centuries ago manage to find Easter Island, for example, and do so at will? If you assume the horizon from say FL100, it is certain that nobody, not even a robot on a windless day, could fly a heading for that distance and end up there. These people were extremely good with the sextant and their tables. The sailors had a table on which to spread their chart and al the time in the world. The early airliners also had a full time pilot or two, a full time engine/fuel manager, and a full time navigator. They also had NDBs and even an NDB is vastly better than dead reckoning.
The trick, as far as I can tell, is that the early navigators (and this includes post-WW2 airliners) had continuous guidance along their track. Even a sextant gives you a line of latitude and is vastly better than dead reckoning and post-WW2 there were NDBs everywhere of interest which are better still. A GPS, like VOR/DME, gives you continuous guidance along a track.
Flyers that did solo transatlantic flights would have tried to use a sextant but in any case would have aimed for an easier target, e.g. the east coast of the USA, or Ireland if coming this way. You've got to do a wind corrected heading to within 5-10 degrees and you will be fine.
The difficulty, which a GPS handles very well, is that today's PPLs get barely enough training to take off, fly an easy XC flight on a perfect day, and land, yet they are expected to fly precise tracks between bits of controlled airspace.
Join Date: Mar 2001
Location: England
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
Fly Stimulator,
Sorry, didn't see the in your post. Apologies. I'll go and stand in the corner - If I can find it.
IO540,
It was a rhetorical question, but thanks for the interesting post. We were using a sextant in the VC10 to cross the Atlantic until the late 80s.
I'll go and sharpen my chinagraph.
Sorry, didn't see the
in your post. Apologies. I'll go and stand in the corner - If I can find it.IO540,
It was a rhetorical question, but thanks for the interesting post. We were using a sextant in the VC10 to cross the Atlantic until the late 80s.
I'll go and sharpen my chinagraph.
Join Date: Mar 2004
Location: UK
Posts: 224
Likes: 0
Received 0 Likes
on
0 Posts
So the locals are not affected by this? Could it be because of the various pronounciations for Sleap and a GPS drop out is punishment for those of us who have tried to pronounce it Sleep?? (I now know better)
Either that or it is a deliberate attempt to confuse those young pilots learning the finer art of rotary flight at the Queen's expense.
Either that or it is a deliberate attempt to confuse those young pilots learning the finer art of rotary flight at the Queen's expense.
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
After a few posts with IO540 about roof mounting and the rest.
I have asked one of a avionics techs andhe assures me that all our units have to be up to class 1 radio fit for BRNAV. which i presumes means arials in the best place checked every year etc etc.
Ours still go tits up on a regular baises. Usually only giving a RAIM error for 5-10 mins then clearing. GPS isn't as good as some make out.
MJ
I have asked one of a avionics techs andhe assures me that all our units have to be up to class 1 radio fit for BRNAV. which i presumes means arials in the best place checked every year etc etc.
Ours still go tits up on a regular baises. Usually only giving a RAIM error for 5-10 mins then clearing. GPS isn't as good as some make out.
MJ
Official PPRuNe Chaplain
Join Date: Apr 2001
Location: Witnesham, Suffolk
Age: 80
Posts: 3,498
Likes: 0
Received 0 Likes
on
0 Posts
I thought RAIM was inbuilt in the receiver?
When I flew with a GPS3Pilot, it would relatively often lose signal for a brief period. That was with an extension antenna (not "arial" - that's a misspelled washing powder) on the windscreen.
Then we had a GNS430 fitted, with a proper antenna mounted on the top of the aircraft. We've never yet had a loss of signal message from that.
When I flew with a GPS3Pilot, it would relatively often lose signal for a brief period. That was with an extension antenna (not "arial" - that's a misspelled washing powder) on the windscreen.
Then we had a GNS430 fitted, with a proper antenna mounted on the top of the aircraft. We've never yet had a loss of signal message from that.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
The capability to do RAIM checking is (or isn't) in the receiver, yes. Few handhelds have it in any form, and none I know of have the proper version which requires an encoding altimeter input, and manual setting of QNH.
Whether you can get RAIM at a given place and time depends on the satellite positions. This can be checked computationally; here is one URL I had saved from a while ago
http://augur.ecacnav.com/
However I don't think RAIM has much relevance to PPL-type en-route flying, and one can hardly use GPS for approaches, as there aren't any in the UK.
Incidentally I haven't seen a RAIM warning in 300 hours (2 years' flying), with a KLN94B. If somebody sees something a lot worse than this, they might consider getting a better avionics engineer
Whether you can get RAIM at a given place and time depends on the satellite positions. This can be checked computationally; here is one URL I had saved from a while ago
http://augur.ecacnav.com/
However I don't think RAIM has much relevance to PPL-type en-route flying, and one can hardly use GPS for approaches, as there aren't any in the UK.
Incidentally I haven't seen a RAIM warning in 300 hours (2 years' flying), with a KLN94B. If somebody sees something a lot worse than this, they might consider getting a better avionics engineer
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
the units are.
http://www.bendixking.com/static/cat...ls.jsp?pid=120
and
http://www.trimble.com/cugr.html
And 300 hours is about 4 months flying for me. I would say on average the signal will drop out maybe 2-3 times a week in nice wx. And if you get stuck in or near heavy rain. ie viz getting down to less than 2k in RA or huge wet clouds for a couple of grand above. If your above the tops it very rarely drops out but does if you go near hot danger areas sometimes.
As for the avionics engineers. They will all be licensed to work on public transport aircraft because thats what I fly, so I presume they know what they are doing before the CAA will let them loose.
MJ
http://www.bendixking.com/static/cat...ls.jsp?pid=120
and
http://www.trimble.com/cugr.html
And 300 hours is about 4 months flying for me. I would say on average the signal will drop out maybe 2-3 times a week in nice wx. And if you get stuck in or near heavy rain. ie viz getting down to less than 2k in RA or huge wet clouds for a couple of grand above. If your above the tops it very rarely drops out but does if you go near hot danger areas sometimes.
As for the avionics engineers. They will all be licensed to work on public transport aircraft because thats what I fly, so I presume they know what they are doing before the CAA will let them loose.
MJ
In all these cases, of course, GPS has not actually failed. It was still working fine. However, local interference is a factor, and that is almost certainly what occurred in these cases. There is a huge difference between an IFR certificated (TSO'd) unit, and a handheld unit. As the frequency spectrum becomes evermore crowded, particularly in Europe, things may get worse. Let's hope Galileo manages to squeeze in somehow, and relieve the situation - though you will have to pay for it, of course.
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
yes I agree there is a huge difference.
But alot of people champion GPS as a 100% reliable system which they can depend on in any wx all the time. When in my experence when it gets horrible and you really need the bloody thing, the atmo conditions are such that there is strong possibility of signal drop.
I was just trying to illustrate that even with the BRNAV IFR GPS which have all the bits and bobs to tell you when its giving you good data. They still loose it occasionally and in my experence its not a rare event. I will admit that the likely error that the units are experencing is far less than the error for those devils devices NDB's
Both those units are certified for GPS approaches in the US.
I am not saying that they arn't great usefull devices. And have done many a IFR leg to intersections using the GPS for track and loosely monitoring the nav with radio nav aids. I just worry that all the chat about them will lull pilots into thinking that the box is god and will never tell a lie. And for the average PPL pilot unless they are very professional in there attitude to flying will tend to go for the easy option and put blind trust in the box. Which could cause a pilot to push on in crap wx when they really should have diverted.
As said on other threads its all about educating the users in the limitations and use of the units. The kit that IO540 has is way out of the league of most UK ppl's. Who after skrimping and saving and watching ebay after xmas may get themselves a very nice moving map colour display. Great but no one explains to them the importance of keeping the database up to date, limitations on using the GPS altitude, the fact that when the wx goes poo thats when you have to watch for signal drop.
BTW out of the 2 units the none graphic trimble is by far the best in my opinion. But its not what people want for VFR flying. In fact both of them are great for what we use it for. But lets face it not much point showing all the controlled airspace or giving warnings that we are in it. We want to be in it as much as possible. So neither of them is a solution for VFR aircraft.
MJ
But alot of people champion GPS as a 100% reliable system which they can depend on in any wx all the time. When in my experence when it gets horrible and you really need the bloody thing, the atmo conditions are such that there is strong possibility of signal drop.
I was just trying to illustrate that even with the BRNAV IFR GPS which have all the bits and bobs to tell you when its giving you good data. They still loose it occasionally and in my experence its not a rare event. I will admit that the likely error that the units are experencing is far less than the error for those devils devices NDB's
Both those units are certified for GPS approaches in the US.
I am not saying that they arn't great usefull devices. And have done many a IFR leg to intersections using the GPS for track and loosely monitoring the nav with radio nav aids. I just worry that all the chat about them will lull pilots into thinking that the box is god and will never tell a lie. And for the average PPL pilot unless they are very professional in there attitude to flying will tend to go for the easy option and put blind trust in the box. Which could cause a pilot to push on in crap wx when they really should have diverted.
As said on other threads its all about educating the users in the limitations and use of the units. The kit that IO540 has is way out of the league of most UK ppl's. Who after skrimping and saving and watching ebay after xmas may get themselves a very nice moving map colour display. Great but no one explains to them the importance of keeping the database up to date, limitations on using the GPS altitude, the fact that when the wx goes poo thats when you have to watch for signal drop.
BTW out of the 2 units the none graphic trimble is by far the best in my opinion. But its not what people want for VFR flying. In fact both of them are great for what we use it for. But lets face it not much point showing all the controlled airspace or giving warnings that we are in it. We want to be in it as much as possible. So neither of them is a solution for VFR aircraft.
MJ
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
MJ
Interesting - are the KLN90 and the Trimble really installed in an airliner? Surely you must have triple inertial nav? I recall looking at a used SEP ~ 2yrs ago which had a KLN90B and I checked it out then; discovered the design was about 8 years old back then. That's a very long time in GPS receivers.
I don't particularly disagree with anything you say. However NOTHING is 100% reliable. Everybody should know that. It is widely assumed that one's brain and the "Mk1 eyeball" (to use the favourite expression of the anti-GPS crowd) are 100% reliable, but they aren't. GPS is a lot more reliable than any other means of en-route nav.
As you suggest, the "IFR approved" units (which were generally intended at the American PPL/IR market which is almost nonexistent in Europe) are not suitable for the average PPL flyer because their moving maps are too small or non-existent. That's why I think fitting a GNS430/KLNxx in a VFR plane is pointless. A much better solution is a GPS with a large MFD or, if you want to save a lot of money and don't have stormscope/radar data to show, a large moving-map GPS like the KMD150. This is a modern product which, with a rooftop aerial, will be highly reliable in reception. Garmin are not a player in that market, for some reason.
You say "Great but no one explains to them the importance of ..." Perhaps this is the real "GPS drawback". Officially, nobody likes it, so nobody is going to tell people about limitations.
Interesting - are the KLN90 and the Trimble really installed in an airliner? Surely you must have triple inertial nav? I recall looking at a used SEP ~ 2yrs ago which had a KLN90B and I checked it out then; discovered the design was about 8 years old back then. That's a very long time in GPS receivers.
I don't particularly disagree with anything you say. However NOTHING is 100% reliable. Everybody should know that. It is widely assumed that one's brain and the "Mk1 eyeball" (to use the favourite expression of the anti-GPS crowd) are 100% reliable, but they aren't. GPS is a lot more reliable than any other means of en-route nav.
As you suggest, the "IFR approved" units (which were generally intended at the American PPL/IR market which is almost nonexistent in Europe) are not suitable for the average PPL flyer because their moving maps are too small or non-existent. That's why I think fitting a GNS430/KLNxx in a VFR plane is pointless. A much better solution is a GPS with a large MFD or, if you want to save a lot of money and don't have stormscope/radar data to show, a large moving-map GPS like the KMD150. This is a modern product which, with a rooftop aerial, will be highly reliable in reception. Garmin are not a player in that market, for some reason.
You say "Great but no one explains to them the importance of ..." Perhaps this is the real "GPS drawback". Officially, nobody likes it, so nobody is going to tell people about limitations.
Carbonfibre-based lifeform
Join Date: Mar 2002
Location: London
Posts: 747
Likes: 0
Received 0 Likes
on
0 Posts
Did a similar debate go on after the introduction of radio nav aids?
I'm too young to remember (don't get to say that very often any more
), but the ability of the ADF in particular to give some rather creative directional suggestions must have caused some people to question its value compared with the well-known infallibility of map, pencil and stopwatch.
I'm too young to remember (don't get to say that very often any more
), but the ability of the ADF in particular to give some rather creative directional suggestions must have caused some people to question its value compared with the well-known infallibility of map, pencil and stopwatch.
Official PPRuNe Chaplain
Join Date: Apr 2001
Location: Witnesham, Suffolk
Age: 80
Posts: 3,498
Likes: 0
Received 0 Likes
on
0 Posts
Horses for courses. The GNS430 is a super piece of kit, and I love it. Used in conjunction with the VOR and ADF, it's ideal.
As backup for a "looking out of the window" VFR flight, it's brilliant. But you do need to keep looking out of the window!
As backup for a "looking out of the window" VFR flight, it's brilliant. But you do need to keep looking out of the window!
Join Date: Mar 2004
Location: UK
Posts: 224
Likes: 0
Received 0 Likes
on
0 Posts
I don't think MJ is flying airliners, and if he flys what I think he flies, he will be using his GPS far more intensively than an average ppl would (or even should - single pilot vs multi pilot).
We use an even older version of GPS receiver, never had too much of a problem with it and whilst I agree the Trimble is excellent, I reckon what we have is even better. Whilst electronics will have advanced over the last ten years, most of that advancement will have been in the user interface and miniturisation rather than a significant improvement in quality or reliability. Indeed, could it been that modern cheaper GPS units be of poorer quality to make them more available to the masses?
I agree GPS is probably the most relaible means of navigation for most pilots, but everyone needs to know the limits and still be able to navigate the old fashioned way. Problem is that other means of nav need practice and if you only ever use GPS, your old skills deminish and you are ill prepared for the fancy black box loosing its fix.
We use an even older version of GPS receiver, never had too much of a problem with it and whilst I agree the Trimble is excellent, I reckon what we have is even better. Whilst electronics will have advanced over the last ten years, most of that advancement will have been in the user interface and miniturisation rather than a significant improvement in quality or reliability. Indeed, could it been that modern cheaper GPS units be of poorer quality to make them more available to the masses?
I agree GPS is probably the most relaible means of navigation for most pilots, but everyone needs to know the limits and still be able to navigate the old fashioned way. Problem is that other means of nav need practice and if you only ever use GPS, your old skills deminish and you are ill prepared for the fancy black box loosing its fix.
Join Date: May 2001
Posts: 10,815
Likes: 0
Received 0 Likes
on
0 Posts
H'mm I don't know if you would call it an airliner more of a multi crew regional turboprop on timetabled routes ( Jetstream 32). It does have a bog fitted though of sorts. We don't have TCAS in any or Auto pilot in most.
You will also find that the trimble is fitted to BA 146's DASH 8's old 737's in fact anything that has a steam driven instrument set that needs BRNAV for flying in controlled airspace would mind betting that Concorde might have had one on as its a BAe machine.
Yes i agree with you IO540 there are alot of political issues with GPS. Who owns it who has control of it etc etc. And as you say nothing is 100% which is why we always check the ident when using enroute VOR's (I might add if its identing test we just go with the GPS
)
I couldn't agree more with the above statement.
I think we both agree on the major points about GPS IO540. Its just that it does have limitations which professionals know about and have been trained / slapped / sworn at / been called slack bastards into always backing up with traditional methods. If it goes tits up on our flights its a very minor annoyance. If your average PPL who flys max 20 hours a year 2 of which is IMC. Who thinks that because they have a GPS on board they can dump the tradional methods because they have set the pink string up. When it does go wrong in WX that they wern't expecting hadn't been in before they won't have the capacity to deal with it. And they won't be up to speed with the traditional methods to just slip striaght over into using them.
The reason why I can be bothered arguing the point is by just having these reruns of the GPS debate it might mean that new PPL's or new GPS users might think "right its a good bit of kit when used properly". As long as they have it in the back of there mind that there is a possibility of it cocking up and they need to plan for that eventuallity my time has not been wasted.
MJ
You will also find that the trimble is fitted to BA 146's DASH 8's old 737's in fact anything that has a steam driven instrument set that needs BRNAV for flying in controlled airspace would mind betting that Concorde might have had one on as its a BAe machine.
Yes i agree with you IO540 there are alot of political issues with GPS. Who owns it who has control of it etc etc. And as you say nothing is 100% which is why we always check the ident when using enroute VOR's (I might add if its identing test we just go with the GPS
)
I agree GPS is probably the most relaible means of navigation for most pilots, but everyone needs to know the limits and still be able to navigate the old fashioned way. Problem is that other means of nav need practice and if you only ever use GPS, your old skills deminish and you are ill prepared for the fancy black box loosing its fix.
I think we both agree on the major points about GPS IO540. Its just that it does have limitations which professionals know about and have been trained / slapped / sworn at / been called slack bastards into always backing up with traditional methods. If it goes tits up on our flights its a very minor annoyance. If your average PPL who flys max 20 hours a year 2 of which is IMC. Who thinks that because they have a GPS on board they can dump the tradional methods because they have set the pink string up. When it does go wrong in WX that they wern't expecting hadn't been in before they won't have the capacity to deal with it. And they won't be up to speed with the traditional methods to just slip striaght over into using them.
The reason why I can be bothered arguing the point is by just having these reruns of the GPS debate it might mean that new PPL's or new GPS users might think "right its a good bit of kit when used properly". As long as they have it in the back of there mind that there is a possibility of it cocking up and they need to plan for that eventuallity my time has not been wasted.
MJ
Red On, Green On
Join Date: May 2004
Location: Between the woods and the water
Age: 24
Posts: 6,487
Likes: 0
Received 2 Likes
on
2 Posts
A friend of mine has an interest in GPS in mobile phones - most new mobiles in the US now have a GPS chipset.
He sent me this:
"GPS is increasingly at risk from a rising noise floor caused by anything from electrical pylons, to WLAN, to faster chips in computers, and many more sources. It is a very weak signal - some 10,000,000 times weaker than GSM for example. It will mean GPS performance gets worse over time, as opposed to the normal trend of improvement."
Clearly an aircraft, when airborne, is some distance away from most of the low power sources, or passing through their influence fast enough not to be affected, but it's worth bearing in mind.
He sent me this:
"GPS is increasingly at risk from a rising noise floor caused by anything from electrical pylons, to WLAN, to faster chips in computers, and many more sources. It is a very weak signal - some 10,000,000 times weaker than GSM for example. It will mean GPS performance gets worse over time, as opposed to the normal trend of improvement."
Clearly an aircraft, when airborne, is some distance away from most of the low power sources, or passing through their influence fast enough not to be affected, but it's worth bearing in mind.
Join Date: Jun 2003
Location: EuroGA.org
Posts: 13,787
Likes: 0
Received 0 Likes
on
0 Posts
It is true that the GPS signal is below the noise floor, but it has special characteristics which enable it to be recovered as well as or better than a signal without those characteristics which is above the noise floor. In principle, a signal can be arbitrarily below the noise floor and still be recovered, if there is sufficient predictable redundancy in it.
I do think that intentional (non-military) jamming is GPS's biggest potential enemy, but again there are ways to provide resistance to that. A rooftop aerial is the starting point.
As MJ suggests, these things are worth discussing.
I do think that intentional (non-military) jamming is GPS's biggest potential enemy, but again there are ways to provide resistance to that. A rooftop aerial is the starting point.
As MJ suggests, these things are worth discussing.