GPS as ADF substitute
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I think different people use the IMC in different ways. I do a lot of en-rout IMC, but being single engine/ no de-ice limited I tend to avoid flying if the cloud is less then 1000 ft AGL.
I have never had to hold, and I would divert if things started to deteriorate. I stay current on approaches, but have only had to do two for real in 10 years, both VOR/DME, with no holds and two planed diversions available into airports with ILS if I needed them.
If I were based at a field which had an ADF element as a compulsory part of the published procedure I would make very sure my ADF was in good order, I would practice it regularly, and I would practice holds if local procedures meant I would need them. In my case non-of the above is true.
On the GPS question, I find it is very useful to be able to draw a picture in my mind of what is happening based on the traditional aids, and then cross check by glancing at the GPS. I find the discipline of doing things in this order to be hard to keep up as the GPS is much more accurate, but I always assume it is about to fail.
If the CAA approved GPS for primary navigation it would hugely reduce workload in the cockpit, but they would also have to insist on proper training to understand the limits and pitfalls of the technology. A badly set up GPS being obeyed regardless is a huge safety hazard. I work in the computer industry, and garbage in garbage out is very relevant to GPS systems.
Rod
I have never had to hold, and I would divert if things started to deteriorate. I stay current on approaches, but have only had to do two for real in 10 years, both VOR/DME, with no holds and two planed diversions available into airports with ILS if I needed them.
If I were based at a field which had an ADF element as a compulsory part of the published procedure I would make very sure my ADF was in good order, I would practice it regularly, and I would practice holds if local procedures meant I would need them. In my case non-of the above is true.
On the GPS question, I find it is very useful to be able to draw a picture in my mind of what is happening based on the traditional aids, and then cross check by glancing at the GPS. I find the discipline of doing things in this order to be hard to keep up as the GPS is much more accurate, but I always assume it is about to fail.
If the CAA approved GPS for primary navigation it would hugely reduce workload in the cockpit, but they would also have to insist on proper training to understand the limits and pitfalls of the technology. A badly set up GPS being obeyed regardless is a huge safety hazard. I work in the computer industry, and garbage in garbage out is very relevant to GPS systems.
Rod
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As as ATCO at a non-radar unit in the uk, I feel it might be worthwhile detailing events which happened some months ago on this very subject. A/c inbound to above unit makes contact, IMC & requesting radar vectors to final approach. Pilot advised that radar is unavailable, and is asked if he is able to effect an approach procedure to land. Pilot responds, 'Looks like I'll have no choice because I'm flying on GPS but it's giving erroneous readings.' He also stated that his nav kit both NDB and VOR weren't functioning 'correctly'. Pilot is instructed to climb to MSA and report overhead the XXX beacon. After a lot of protracted R/T, I became very aware that this pilot was hopelessly lost and utterly dependent on his 'erroneous' GPS. This particular pilot was almost pleading for radar assistance at an airfield which was totally unable to provide it. After 30mins of dialogue between pilot, D&D and other nearby radar units, (although not near enough to give vectors AND descent) the a/c was identified at 800ft in an area of high terrain of 2400ft in IMC. Ultimately the pilot was lucky enough to get enough surface contact to effect a landing. After landing, his nav kit was checked and found to be perfectly serviceable but simply turned off. This pilot did not know how to navigate on standard instruments and was basically a GPS pilot. When the GPS failed, he was lucky to escape disaster. Be warned!!!
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"I have a GPS III Pilot, which I use purely as a secondary navaid, and wondered if it is considered acceptable to use this as a substitute ADF?"
Of course not, an ADF is a LF/MF direction finder that can only be used in conjunction with an NDB. The latter is a Point Navigation Aid which permits you to know exactly where you are when you are in the overhead.
GPS is an area Navigation Aid which whilst generally being of high accuracy, gives no indication of when it is not accurate. It lacks the basic simplicity of an ADF/NDB combination which provides you with a positive fix when you are directly over the NDB.
All area nav aids must be cross checked with an alternative nav Aid, in the case of GPS, there is no other aid with the same potential accuracy against which it can be checked.
Of course not, an ADF is a LF/MF direction finder that can only be used in conjunction with an NDB. The latter is a Point Navigation Aid which permits you to know exactly where you are when you are in the overhead.
GPS is an area Navigation Aid which whilst generally being of high accuracy, gives no indication of when it is not accurate. It lacks the basic simplicity of an ADF/NDB combination which provides you with a positive fix when you are directly over the NDB.
All area nav aids must be cross checked with an alternative nav Aid, in the case of GPS, there is no other aid with the same potential accuracy against which it can be checked.
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Do we inhabit different parallel universes, Noggin? Or did I just miss a smiley? 
My experience of the ADF is that it is a hopelessly flakey navigation system with multiple failure modes that allow single-point failures to cause erroneous readings without any warning at all.
ADFs can easily lose a signal from an NDB, in which case most cockpit equipment gives no alarm signal. Cards can stick to one another as they turn. In 1978 a Cessna 188 got lost over the Pacific when the needle of the ADF indicator became lose on its spindle, and simply pointed wherever it wanted -- the aircraft was saved by an Air NZ crew that located it. ADFs experience erroneous reading around thunderstorms, coastlines and even when pointing towards certain parts of the aircraft in which they are installed, or when the aircraft is in a particular attitude. If a new navigational aid of similar "reliability" were proposed today, it wouldn't clear the first hurdle of a risk assessment.
By contrast, even hand-held GPS units tend to give the pilot an indication of their inability to navigate accurately, though that's not guaranteed without RAIM.
In ClassGMaster's example, the pilot was at least aware that the GPS wasn't working (and there's no excuse for getting yourself into a predicament like that with the failure of any single navigational device). If the authorities were to embrace GPS for the potential aid to safety that it can be, rather than telling pilots of the dreadful disasters that can befall them with this evil device, we might manage to reverse some of the contempt that GA pilots have for the CAA's ability to manage risk on their behalf. The double standards that seem to be applied are transparent to anyone who's been called upon to do a H&S risk assessment for so much as a 3-man office of paperpushers.
My experience of the ADF is that it is a hopelessly flakey navigation system with multiple failure modes that allow single-point failures to cause erroneous readings without any warning at all.
ADFs can easily lose a signal from an NDB, in which case most cockpit equipment gives no alarm signal. Cards can stick to one another as they turn. In 1978 a Cessna 188 got lost over the Pacific when the needle of the ADF indicator became lose on its spindle, and simply pointed wherever it wanted -- the aircraft was saved by an Air NZ crew that located it. ADFs experience erroneous reading around thunderstorms, coastlines and even when pointing towards certain parts of the aircraft in which they are installed, or when the aircraft is in a particular attitude. If a new navigational aid of similar "reliability" were proposed today, it wouldn't clear the first hurdle of a risk assessment.
By contrast, even hand-held GPS units tend to give the pilot an indication of their inability to navigate accurately, though that's not guaranteed without RAIM.
In ClassGMaster's example, the pilot was at least aware that the GPS wasn't working (and there's no excuse for getting yourself into a predicament like that with the failure of any single navigational device). If the authorities were to embrace GPS for the potential aid to safety that it can be, rather than telling pilots of the dreadful disasters that can befall them with this evil device, we might manage to reverse some of the contempt that GA pilots have for the CAA's ability to manage risk on their behalf. The double standards that seem to be applied are transparent to anyone who's been called upon to do a H&S risk assessment for so much as a 3-man office of paperpushers.
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Our experiences quite clearly differ. I have used the ADF reliably all over the World for many years. Whilst it has many short commings, its simplicity has resulted in it being the longest lasting radio navigation aid. As for not having any warnings or indications, you only have to listen to it.
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Noggin: Once I was flying Northbound over the Kalahari using the few ground features available to check my postition (something like a specific tree or a dry pond,...).
The A/C I flew was equipped with a wonderful ADF (not my opinion) and later during the flight I began to get a strong signal (audio) and a clear indication of where the needle wanted to go. Great I thought!! Those things really work. Well, not quite because after a little while, despite listening the identifier I realised I couldn't tell where I was anymore. As a matter of fact I could see very large pan that I had never seen before (having done the route regularly). Was I still in the same country or across the border (over a country filled with land mines
). I really didn't know so when I finally spotted a village, without hesitation I landed nearby. I then walked to the local school where the teacher very kindly gave my a lesson of geography on one of these map you get in any classroom.
The irony was that I was actually carrying a GPS on board.... but in the pod
Needless to say that even when I get a very good NDB ident, I don't trust them much anymore.
Makes me laugh when someone tries to tell me how wonderful NDBs are because they aren't. GPS aren't perfect either but I know which one I prefer when flying single pilot SE/IFR in storm(ADF love it)/icy conditions.
For information, we don't shoot GPS approaches but we are BRNAV and when on our homebase NDB approach, we like to monitor it with the GPS. Much better for situation awareness.
Safe Flying.
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If you can't save the engine...save the airframe
The A/C I flew was equipped with a wonderful ADF (not my opinion) and later during the flight I began to get a strong signal (audio) and a clear indication of where the needle wanted to go. Great I thought!! Those things really work. Well, not quite because after a little while, despite listening the identifier I realised I couldn't tell where I was anymore. As a matter of fact I could see very large pan that I had never seen before (having done the route regularly). Was I still in the same country or across the border (over a country filled with land mines
). I really didn't know so when I finally spotted a village, without hesitation I landed nearby. I then walked to the local school where the teacher very kindly gave my a lesson of geography on one of these map you get in any classroom. The irony was that I was actually carrying a GPS on board.... but in the pod
Needless to say that even when I get a very good NDB ident, I don't trust them much anymore.
Makes me laugh when someone tries to tell me how wonderful NDBs are because they aren't. GPS aren't perfect either but I know which one I prefer when flying single pilot SE/IFR in storm(ADF love it)/icy conditions.
For information, we don't shoot GPS approaches but we are BRNAV and when on our homebase NDB approach, we like to monitor it with the GPS. Much better for situation awareness.
Safe Flying.
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If you can't save the engine...save the airframe
Guest
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When your only navaids are an ADF, a driftsight and a astrocompass the ADF starts to look pretty good. Nobody had thought of GPS then.
I made no comment about the accuracy of ADF, except in the overhead, when you can be pretty certain that you know where you are. GPS may be good, but it lacks the certainty.
The original question asked if GPS was a substitute for an ADF, it is not. It does make a good alternative, and is even better if one compliments the other.
I made no comment about the accuracy of ADF, except in the overhead, when you can be pretty certain that you know where you are. GPS may be good, but it lacks the certainty.
The original question asked if GPS was a substitute for an ADF, it is not. It does make a good alternative, and is even better if one compliments the other.
Guest
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GPS does have a couple of faults. The biggest is it can't tell you are precisely in the 'overhead' of a 10000 feet mountain you erroneously programmed in as Aerodrome X 201 feet amsl.
The other is when it isn't working. Well a)they nearly always work and b) you should normally notice that Groundspeed=0 doesn't fit in with the other bits of your scan.
I would remind you the biggest plus point over everything else (for private pilots) is they cost £100. Ergo you can have two, or three. Don't tell me two or three different makes of GPS all fail together very often.
If ever.
I should add I suspect lots of people seem to think GPS=MAP. Not so. I don't have a map therefore I can tell when I am 0.01nm from the overhead. The reason is it says 0.01 nm. Much better than any ADF.
The other is when it isn't working. Well a)they nearly always work and b) you should normally notice that Groundspeed=0 doesn't fit in with the other bits of your scan.
I would remind you the biggest plus point over everything else (for private pilots) is they cost £100. Ergo you can have two, or three. Don't tell me two or three different makes of GPS all fail together very often.
If ever.
I should add I suspect lots of people seem to think GPS=MAP. Not so. I don't have a map therefore I can tell when I am 0.01nm from the overhead. The reason is it says 0.01 nm. Much better than any ADF.
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Noggin
I question your response. What's you evidence?
Error in GPS is unlikely to be common to all 24 satellites. You only need 4. You typically can pick up 6, 7, 8 upwards. You'll appreciate that gives many calculation permutations.
Even if all 3 GPS were identical they may still lock onto to different satellites and thus not share the same error.
If they are different, which is what I said, then you have the benefit of different averaging algorithms to iron out the effects of error.
My GPS tracks 8 satellites but only in rotation. I'm sure more expensive ones can track several simultaneously. No doubt that produces differences in the calculations.
So what error (apart from interference/jammimg) do you think GPS is affected by that can cause you a problem on two different receivers, assuming you are not down to the minimum 4 satellites?
Incidentally my £100 GPS has an RMI which visually shows passing a waypoint just like an ADF, and it automatically moves to the next waypoint as another visual cue.
I question your response. What's you evidence?
Error in GPS is unlikely to be common to all 24 satellites. You only need 4. You typically can pick up 6, 7, 8 upwards. You'll appreciate that gives many calculation permutations.
Even if all 3 GPS were identical they may still lock onto to different satellites and thus not share the same error.
If they are different, which is what I said, then you have the benefit of different averaging algorithms to iron out the effects of error.
My GPS tracks 8 satellites but only in rotation. I'm sure more expensive ones can track several simultaneously. No doubt that produces differences in the calculations.
So what error (apart from interference/jammimg) do you think GPS is affected by that can cause you a problem on two different receivers, assuming you are not down to the minimum 4 satellites?
Incidentally my £100 GPS has an RMI which visually shows passing a waypoint just like an ADF, and it automatically moves to the next waypoint as another visual cue.
Guest
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Okay then, what about my experience of yesterday. I was providing combined tower and approach control in Class G. The airfield VOR failed. Some hours later the colocated DME failed. I was fortunate to still have an airfield NDB which I used to hold aircraft, and also to provide standard separation and also for instument approaches. I had several IFR inbounds/outbounds and overflights. This was a mixture of scheduled public transport flights and GA traffic. The weather was solid IMC. At one point I had a stack up to 8000 altitude HOLDING on the NDB AND making NDB approaches. I had 5 TBM700s holding on the NDB at one point. If you think you'll never be asked to hold on an NDB and fly a subsequent approach, think again.
Guest
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Thats right Jayemm, if the cloud ceiling is circa 300ft you would have to divert to an airfield with a serviceable VOR/DME to fly the approach.
Perhaps the fact that the NDB approach has an OCH of 300ft doesn't bother you. Our NDB is bang on runway centreline and on the coast and therefore doesn't suffer coastal refraction. But if you prefer, divert to the nearest airfield (31DME North) and fly their VOR/DME(OCH 600ft). After you've gone around a few times, try the next nearest airfield (100DME+) to the south.
If you get lucky and make a successful approach, wipe your brow and think about getting the ADF fixed.
Perhaps the fact that the NDB approach has an OCH of 300ft doesn't bother you. Our NDB is bang on runway centreline and on the coast and therefore doesn't suffer coastal refraction. But if you prefer, divert to the nearest airfield (31DME North) and fly their VOR/DME(OCH 600ft). After you've gone around a few times, try the next nearest airfield (100DME+) to the south.
If you get lucky and make a successful approach, wipe your brow and think about getting the ADF fixed.
Guest
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OK, point taken and chastisement received. I've now got to persuade a share group which has one very experienced pilot (IMC) who seems not unhappy with a u/s ADF, and all others PPL only, to fork out to fix the ADF.
Which airfield were you talking about anyway?
Which airfield were you talking about anyway?
Guest
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I have only just opened this thread and have read it through, and I think it has got away from the nub of the issue as I see it. If you are flying IFR (IMC or not) you must have the equipment and skills to allow you to complete that flight safely. Since the CAA does not yet see fit to agree to the use of GPS as a primary navigation aid (which is wahat the original question was suggesting) then you need to be competent in the interpretation and operation of those navaids which are permitted. Much discussion has been had about NDB holding and I personally cannot see what all the fuss is about. If you go and practice them (on your PC if available) after perhaps a briefing from someone who knows and understands them, I bet that you will soon get them cracked. Look elsewhere in this forum for info on how to calculate drift easily, and you will be home and dry.
I worry about those who suggest that it's OK to go flying with less than the necessary skills or equipment because they can always divert to somewhere those are not needed. The point has already been admirably made about the potential hazards of that policy. Surely you should not be contemplating going flyin with the knowledge that your skills which ultimately your life may depend upon are not up to scratch. It's like saying that your crosswind landings are crap but it doesn't matter because you will only fly to airfields with an into-wind runway. What about when there isn't one or you haven't got enough fuel to get to it?
ILS and VOR and Radar are very reliable, but they DO fail, and if your lifesaver is an NDB hold and approach, then I would think to learn how to fly one is a small price to pay. It's costing you enough to be up there anyway, so why not make sure you can do the job properly.
By the way, I have also had to fly an NDB hold and approach for real when I had expected a radar vectored ILS. It does happen.
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"Take-off is optional, Landing is mandatory"
I worry about those who suggest that it's OK to go flying with less than the necessary skills or equipment because they can always divert to somewhere those are not needed. The point has already been admirably made about the potential hazards of that policy. Surely you should not be contemplating going flyin with the knowledge that your skills which ultimately your life may depend upon are not up to scratch. It's like saying that your crosswind landings are crap but it doesn't matter because you will only fly to airfields with an into-wind runway. What about when there isn't one or you haven't got enough fuel to get to it?
ILS and VOR and Radar are very reliable, but they DO fail, and if your lifesaver is an NDB hold and approach, then I would think to learn how to fly one is a small price to pay. It's costing you enough to be up there anyway, so why not make sure you can do the job properly.
By the way, I have also had to fly an NDB hold and approach for real when I had expected a radar vectored ILS. It does happen.
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"Take-off is optional, Landing is mandatory"
Guest
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In reply to eyeinthesky,
A colleague of mine contacted me tonight to tell me that there had been a couple of additions to the Forum. I have to agree with what he said, which was that your post was a pretty damn good summary of the debate. Nothing further to add!
[This message has been edited by ClassGMaster (edited 03 July 2001).]
A colleague of mine contacted me tonight to tell me that there had been a couple of additions to the Forum. I have to agree with what he said, which was that your post was a pretty damn good summary of the debate. Nothing further to add!
[This message has been edited by ClassGMaster (edited 03 July 2001).]
Guest
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eyeinthesky wrote:
I'm still waiting to be told precisely which legislation requires me to have and use an ADF for these procedures outside controlled airspace.
Nor am I aware of a concept of a 'primary navigation aid' within UK law.
I don't disagree with the general sentiment of your post. Certainly, it helps to learn and practice a whole range of procedures for both VFR and IFR flying. But training and practice has to be prioritised and there is a limit to what one can do in finite time. How much time do you spend practising VDF or QGH approaches in case that ADF fails.
I think we need to be a little more pragmatic about training people for IFR flight. There are very few accidents that have occurred because pilots were incapable of flying an NDB approach -- and none because they were incapable of flying an NDB hold. Most IFR accidents involving less experienced pilots are due to either of loss of control when a pilot is under a heavy workload, or CFIT caused by a lack of situational awareness of the surrounding terrain. I'm not convinced that teaching pilots to fly perfect racetracks on a WWII nav system prepares pilots adequately for the real world.
<font face="Verdana, Arial, Helvetica" size="2">If you are flying IFR (IMC or not) you must have the equipment and skills to allow you to complete that flight safely. Since the CAA does not yet see fit to agree to the use of GPS as a primary navigation aid (which is wahat the original question was suggesting) then you need to be competent in the interpretation and operation of those navaids which are permitted. </font>
Nor am I aware of a concept of a 'primary navigation aid' within UK law.
I don't disagree with the general sentiment of your post. Certainly, it helps to learn and practice a whole range of procedures for both VFR and IFR flying. But training and practice has to be prioritised and there is a limit to what one can do in finite time. How much time do you spend practising VDF or QGH approaches in case that ADF fails.
I think we need to be a little more pragmatic about training people for IFR flight. There are very few accidents that have occurred because pilots were incapable of flying an NDB approach -- and none because they were incapable of flying an NDB hold. Most IFR accidents involving less experienced pilots are due to either of loss of control when a pilot is under a heavy workload, or CFIT caused by a lack of situational awareness of the surrounding terrain. I'm not convinced that teaching pilots to fly perfect racetracks on a WWII nav system prepares pilots adequately for the real world.
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Bookworm
I agree. I'm sticking with what I said earlier. You can use a GPS for IFR flight. You can use a very large pepper mill if you want. You do not have to look out the window and map read as Keef suggests. (Not recommended in IMC)
You cannot use a GPS for approaches ie coming below 1000 feet above the highest object within 5 miles (10?).
However as I said earlier, in general, if you are doing a hold you are possibly in a situation that requires a working ADF whether or not you are using it at the time eg you are on airways or you are flying in Class A or D TMAs (see ANA?) or you are a BA pilot etc see (SOPs) etc.
As regards the discussion on how to keep in pratice, the only difference with an ADF versus VOR/DME or GPS is you don't have a miles read-out. This is only the same as a VOR with unavailable DME so you should be able to do this anyway.
I agree. I'm sticking with what I said earlier. You can use a GPS for IFR flight. You can use a very large pepper mill if you want. You do not have to look out the window and map read as Keef suggests. (Not recommended in IMC)
You cannot use a GPS for approaches ie coming below 1000 feet above the highest object within 5 miles (10?).
However as I said earlier, in general, if you are doing a hold you are possibly in a situation that requires a working ADF whether or not you are using it at the time eg you are on airways or you are flying in Class A or D TMAs (see ANA?) or you are a BA pilot etc see (SOPs) etc.
As regards the discussion on how to keep in pratice, the only difference with an ADF versus VOR/DME or GPS is you don't have a miles read-out. This is only the same as a VOR with unavailable DME so you should be able to do this anyway.
Guest
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<font face="Verdana, Arial, Helvetica" size="2">You cannot use a GPS for approaches ie coming below 1000 feet above the highest object within 5 miles (10?).</font>
<font face="Verdana, Arial, Helvetica" size="2">However as I said earlier, in general, if you are doing a hold you are possibly in a situation that requires a working ADF whether or not you are using it at the time eg you are on airways or you are flying in Class A or D TMAs (see ANA?) or you are a BA pilot etc see (SOPs) etc.</font>
By contrast, I've frequently been asked to hold on NDBs at airports with procedural approach control for IFR, the majority of which are outside controlled airspace.
<font face="Verdana, Arial, Helvetica" size="2">As regards the discussion on how to keep in pratice, the only difference with an ADF versus VOR/DME or GPS is you don't have a miles read-out. This is only the same as a VOR with unavailable DME so you should be able to do this anyway.</font>
I don't doubt that some instrument approach practice is better than none, but I do believe that if you're going to use a radio of any sort for an IAP, you did need to keep proficient in using it -- and that applied as much to GPS as anything else.
I like to fly almost every approach with as much redundancy as possible. Trouble is, if you told me I had to switch off either the ADF or the GPS on an NDB approach, I'd have a struggle justifying a choice to switch off the GPS on risk management grounds.