GPS as ADF substitute

[jayemm]

I fly a Warrior with average Navaids (VOR/ILS/COM/ADF), but the ADF is u/s and the group isn't motivated to produce the money to fix it.

Having used the ADF (different PA28) for my IMC training, I miss it now.

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?

Also, I haven't done any instrument landings in the 9 months since getting the IMC, but wanted to know your views on using the GPS as an ADF substitute on NDB holds? (I don't plan to try any IAs without refresher training!)

[Keef]

If GPS satellite coverage is OK, then it will work fine. BUT it's not "acceptable" to the authorities as a primary navaid, so if you use your GPS III you are VFR looking out of the window as far as navigation is concerned.

The fact that it's more accurate and more reliable than ADF doesn't count.

In short - be careful!

Keef

[ShyTorque]

As Keef said, the answer to your question is unfortunately a BIG NO.

The CAA would hang you out to dry if they found out you were attempting a procedure without the relevant navaid.

ShyT

[twistedenginestarter]

We are talking here about holds. I don't think there is any rule that says you can't use a GPS for holds.

You can use what you like for en route ,as far as I am aware, as long as you remain at a safe altitude and carry the equipment mandated for the class of airspace you are in and class of flying you are carrying out.

There again if you are needing to do a hold you probably also need to have a working ADF so it may not help you...

[jayemm]

Thanks. As I suspected the answer is no. That rules out any ILS approaches which entail the NDB-hold only option then! So it should be VOR-holds or not at all.

[bookworm]

I can find no piece of legislation that requires the carriage or use of an ADF to fly an ILS approach, or even an NDB approach, OUTSIDE controlled airspace.

AFAICS, the only way in which you could be "hung out to dry" would be on the basis of endangering the aircraft. Welcome to the mid-grey area of executive risk management. :)

[Flybywyre]

As a point of interest has anyone ever been asked to take up a NDB hold and procedure? (light aircraft PA28's etc)
I've been flying for 14 years and renewed my IMC 3 times and I have never been asked to take up an NDB hold. In fact I can't remember being asked to take up ANY procedure, I have been told to hold (orbit) at current position....and then vectored on to the ILS, but I can't recall ever being requested to take up the hold and proceedure. I don't bother flying IMC these days but when I did I always had to ask to take up the procedure in order to get the practice in. I used to do some serious IMC approach's into EGHI and used to enjoy doing the VOR/DME proceedure, but I always had to request it. Makes sense really because it is far easier to be vectored than mess about trying to fly NDB holds etc. Just wondered if anyone else has had simillar experiences.
Regards
FBW

['I' in the sky]

Bookworm.
Legislation requires you to carry navaids appropriate to the type of approach to be flown which would seem to imply, given that GPS overlay approaches are not yet approved in our airspace, that you need to carry an ADF. Further to that even where they are approved, ie US, you are still required to have the appropriate navaids aswell as your GPS.

Given that most ILS approaches in this country use an NDB as the IAF it also seems reasonable that you need to carry an ADF to legally fly an ILS unless of course radar unserviceability is something which will never happen to you.

Also before trust your life to a GPS, the "No GPS position available" message is something which I have seen more than once.

[bookworm]

<font face="Verdana, Arial, Helvetica" size="2">Legislation requires you to carry navaids appropriate to the type of approach to be flown which would seem to imply, ...</font>

Which legislation in particular, please? Which article of the ANO or Rule of the Air?

[This message has been edited by bookworm (edited 11 June 2001).]

[jayemm]

Flybywyre

Interesting point. I only worried about the NDB holds because I did them in training. If you're not commercial/professional (like me) and are only likely to be asked to orbit (which I've done several times), then do I really need to worry about keeping proficient in NDB holds? Your question begs another one that, if you have an IMC on the basis of safety/contingency, rather than regular and necessary flight in IMC conditions, then can you rely on vector approaches (SRA) (and keep practiced of course) rather than worrying about all instrument approaches? If memory is correct, on qualification for the IMC you get to choose one type of instrument approach anyway.

Interested in views on this.

[Chilli Monster]

Flybywyre

NDB Holds are necessary at airfields without radar or indeed for NDB approaches themselves - have a look at the Approach plate for Rwy 22 at Cranfield. Plymouth and Sheffield will be the same. I've also been the pax in a Fokker 100 when the radar was out at East Mids - again holding was necessary to sequence us and the UPS 767 below us.

Bookworm

ANO Sched 5 and Article 15 are the reading that you want :)

CM

[This message has been edited by Chilli Monster (edited 12 June 2001).]

[Flybywyre]

Chilli Monster...............

Rather than stating the obvious I think we would all be more interested in any comments you have regarding the question I raised in my post.

Regards
FBW

[Oshkosh]

FBW

I did my instrument training at Oxford - also non-radar - if the conditions were IMC, we would generally have to hold, regardless of training requirements, as they can only have one IFR aircraft in the procedure at a time (hence we used to cancel IFR as soon as we broke cloud on the procedure).

I have also had to hold at Cranfield and Gloucester in IMC for similar reasons.

Any radar-equipped airfield, as you say, will tend to just vector you onto the approach rather than make you sit in the hold.

[Chilli Monster]

FBW

I thought I was - but I'll put it simply for you ;)

YES - I HAVE BEEN ASKED TO FLY A HOLD IN IMC (In a Warrior).

YES - IT IS NECESSARY TO KNOW HOW TO.

If you want to fly in IMC then you should know how to do everything that may be required of you - not just pick the bits that you feel like! If you can't then what are you going to do on the day that you are expected to. Although holds are a throw back to the days of non-radar they are still necessary in certain places (So your question 'has anyone been asked to do them?' will get a 'Yes' answer - which is basically what I gave you).

Bear in mind that holds are not just there as part of an Approach procedure. The likes of Oxford actually stack their IFR arrivals in theirs during that phase of their flying. You might also have to hold over an NDB for weather improvement.

CM


[This message has been edited by Chilli Monster (edited 14 June 2001).]

[Flybywyre]

Chilli Monster..............

Pleased to see that you are catching up, lets have one last try. Here is the question again:
"As a point of interest has anyone ever been asked to take up a NDB hold and procedure? (light aircraft PA28's etc)

Hopefully the highlight will enable you to answer the question (the only question that I asked) in its entirety this time. A simple Yes or No will more than suffice.
Off to the flying club for a beer now.....

Cheers..... http://www.stopstart.fsnet.co.uk/smilie/guin.gif

[This message has been edited by Flybywyre (edited 14 June 2001).]

[This message has been edited by Flybywyre (edited 14 June 2001).]

[Applycarbheat]

FBW's question is quite clear if you read it properly.
My answer: NO
Regards
ACH

[Cusco]

Fly by wire asked if anyone had been asked to take up an |NDB hold.

The answer in my case is yes: in E Anglia there is a distinct shortage of nice accurate VORs and for two of my last four IMC renewals I've been asked to hold at NH at Norwich.

Ok in still Wx but in half a November gale not much fun.

I'm a great believer in GPS but even with my fantastic Garmin 295 there is a bit of satellite shortage consistently over the north Norfolk coast.

However with the help of another ppruner and some accurate map plotting it was not too difficult to work out (just for idle interest and use in VMC only you understand) a bl**dy accurate ILS approach to a tiny bit of grass in the middle of nowhere.

NDB s are cool GPs is cooler


Safe flying

Cusco

[Chilli Monster]

FBW

My apologies for not answering in the matter that you would have liked - however, as you have requested -

YES

(By the way - it is well known that sarcasm is the lowest form of wit ;))

CM


[This message has been edited by Chilli Monster (edited 15 June 2001).]

[Rod1]

Just a thought

I do not think holds of any kind are a compulsory part of the IMC qualification. I have certainly never been tested on them at any time in the last ten years, either as part of my original IMC test, or any of my renewals.

[jayemm]

In reply to ROD1, during my training I was told that holds are not essential and won't be tested (they weren't). But I agreed with my Instructor that it would be pretty essential to learn how to do them.

So, why does the IMC not mandate and test them, when from the thread so far it seems as though it might be essential to know how to hold?

[Rod1]

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

[Flybywyre]

Chilli Monster..........

Thanks for the reply.

Regards
FBW

[ClassGMaster]

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!!!

[Noggin]

"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.

[bookworm]

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.

[Noggin]

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.

[AMEX]

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 http://www.pprune.org/ubb/NonCGI/frown.gif ). 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 http://www.pprune.org/ubb/NonCGI/frown.gif
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.


------------------
If you can't save the engine...save the airframe :D
http://www.stopstart.fsnet.co.uk/mica/MiscDancfrog.gif

[Noggin]

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.

[twistedenginestarter]

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.
;)

[Noggin]

The remarkable thing about GPS is that 3 sets together will invariably have the same system errors. It is seldom the receiver that fails.

[twistedenginestarter]

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.

[ClassGMaster]

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.

[jayemm]

Blimey! That's scary. So me with my u/s ADF, but working GPS would have had to divert to airfield with VOR/DME in use.

[ClassGMaster]

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.

[jayemm]

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?

[eyeinthesky]

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.



------------------
"Take-off is optional, Landing is mandatory"

[ClassGMaster]

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).]

[bookworm]

eyeinthesky wrote:

<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>

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.

[twistedenginestarter]

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.

[bookworm]

<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>

All I'm looking for is where it says in legislation that I cannot.

<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>

There is no doubt that an ADF is required for IFR flight in class A or D airspace. It doesn't matter if you need to use it or not. I would actually contest your observation, if I understand it correctly, that you are most likely to be asked to do an NDB hold in class A or D airspace. I think it's highly unlikely, and I can't remember a time that I have been required to hold in controlled airspace. That's because the vast majority of class A/D environments are managed by radar-equipped units and, bar the majors like Heathrow and Gatwick, most traffic is managed by vectoring. Even where holds are required at Heathrow and Gatwick, most are on VORs.

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'm amazed that you regard the three types of approach as similar. They have vastly different user interface demands, traps for the unwary, instrument errors and failure modes. I've yet to find a GPS with dip, or an ADF that would tell me my track over the ground.

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.

[eyeinthesky]

Bookworm:

I have been doing a bit of checking through the ANO in my spare time (sad, I know).

As far as I can see, you are right that the schedule of radio equipment to be carried unde IFR outside CAS makes no mention of ADF (or any other nav equipment, for that matter).

What might catch you legally is Article 14 (7) which says that any equipment used for navigation, including 'information from selected celestial bodies'(or something like that) must be approved by the CAA. As I understand it a GPS fitted into an aircraft becomes a mod which must be approved. A handheld one doesn't, provided you don't attach it to the yoke.

In addition, Article 15 says equipment carried must be in a serviceable condition and of a type approved in relation to the purpose it is used. If GPS is not approved as an ADF substitute then you are stuck.

Article 16 says that all radio equipment must be approved. Does GPS come under radio equipment?

What I couldn't find were any details on the approval or otherwise of GPS. However, it is clear that you must not descend below MSA except for purpose of landing and on an approach procedure unless you are below 3000' AMSL and clear of cloud and in contact with the ground. As far as I know there are no approved GPS approaches in this country.

So we are not much further legally, but I still stand by my original comments. Sorry for the tedious type of reference to the ANO, but you started it!




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"Take-off is optional, Landing is mandatory"

[john_tullamarine]

The posts so far don't seem to address the basic reliability and accuracy concerns with GPS. Without preprogrammed RAIM monitored approaches (which exist in many places for non precision type letdowns) the use of the system entails an unpredictable risk. Likewise with holding if there is a concern with traffic separation or terrain clearance (as in protected areas).

GPS is great as a backup tool and for assisting with the initial above MSA tracking into the often poor range of an NDB .... but, without the added reliability of RAIM and DGPS for more precise approaches, it is a bit of a suckerbait system.

It horrifies me to see GA pilots here program their own versions of the published letdowns .. and then proceed to fly them ....


[This message has been edited by john_tullamarine (edited 04 July 2001).]

[bookworm]

<font face="Verdana, Arial, Helvetica" size="2">I have been doing a bit of checking through the ANO in my spare time (sad, I know).</font>

No sadder than my contributions, and, as you pointed out, I did start it! :)

<font face="Verdana, Arial, Helvetica" size="2">What might catch you legally is Article 14 (7) which says that any equipment used for navigation, including 'information from selected celestial bodies'(or something like that) must be approved by the CAA. As I understand it a GPS fitted into an aircraft becomes a mod which must be approved. A handheld one doesn't, provided you don't attach it to the yoke.</font>

That's a very fine attempt but I don't think GPS qualifies -- it's a trilateration (distance measuring) technique and the article seems to be refering to altitudes and bearings from stars.

<font face="Verdana, Arial, Helvetica" size="2">In addition, Article 15 says equipment carried must be in a serviceable condition and of a type approved in relation to the purpose it is used. If GPS is not approved as an ADF substitute then you are stuck.</font>

That's certainly getting closer. But it refers to installed equipment, and therefore not handheld GPSs. It's certainly arguable that a panel-mount GPS with a Flight Manual supplement saying "VFR-only" could not be used to fly an IFR approach.

<font face="Verdana, Arial, Helvetica" size="2">Article 16 says that all radio equipment must be approved. Does GPS come under radio equipment?</font>

I'm not quite with that. Article 16 appears to say that all required equipment must be serviceable.

<font face="Verdana, Arial, Helvetica" size="2">What I couldn't find were any details on the approval or otherwise of GPS.</font>

I don't know of any in the ANO. GPS seems to have a funny status -- certain units can be used to satisfy BRNAV requirements.

<font face="Verdana, Arial, Helvetica" size="2">However, it is clear that you must not descend below MSA except for purpose of landing and on an approach procedure unless you are below 3000' AMSL and clear of cloud and in contact with the ground. As far as I know there are no approved GPS approaches in this country.</font>

This is the contention that I really have trouble with. The Rules of the Air don't say anything of the sort!

Rule 29 says:
"Without prejudice to the provisions of rule 5, in order to comply with the Instrument Flight Rules an aircraft shall not fly at a height of less than 1000 feet above the highest obstacle within a distance of 5 nautical miles of the aircraft unless:
(a) it is necessary for the aircraft to do so in order to take off or land;
(b) the aircraft is flying on a route notified for the purposes of this rule;
(c) the aircraft has been otherwise authorised by the competent authority; or
(d) the aircraft is flying at an altitude not exceeding 3000 feet above mean sea level and remains clear of cloud and in sight of the surface."

It says nothing about "on an approach procedure" or anything of the sort. Just if "it is necessary for the aircraft to do so in order to take off or land".

What seems to be "obvious" but missing is any requirement to:

a) make use of an IAP
b) use particular equipment when flying an IAP

Let's just get this thing in perspective. I'm not seriously suggesting that it's wise to make up approach procedures, or rely on a handheld GPS in circumstances when it's operation is critical. (I think it's equally if not more daft to rely on an ADF!) What I am saying is that outside controlled airspace UK air law places few restrictions on the pilot to operate in a particular way. That requires a healthy and thorough attitude to risk management.

I think that the attitudes pushed by the CAA of continually damning GPS distort the ability to manage risk and present an unhelpful picture which is at odds with most pilots' everyday experiences. When you keep getting "advice" which is blatantly at odds with experience and common sense, you learn to ignore it. There are real risks with GPS.

I do not believe that the CAA does pilots any favours by accepting 'status quo' technologies, while placing great burdens on the introduction of new and clearly superior technologies. The FAA has had a GPS overlay program for more than 5 years, and I've not even read of an incident let alone an accident attributed to a GPS approach.

It's all very well for AP to sit there and say to airport operators "sure, we'll consider your request for a GPS approach -- just make out the cheque to...". The FAA had the foresight to realise that GPS could be an enormous benefit to civil aircraft safety, and to move forward in a way that improved overall IFR safety. But it wasn't invented here, was it?

[Keef]

I've just emerged from reading the US FAR/AIM (sad, but necessary towards the FAA IR). That has some stern warnings about use of GPS, and some very enlightened ones.

RAIM is NOT the same as DGPS - your panel-mount IFR-approved GPS cross-checks itself against "spare" satellites and yells if it thinks it's going skewed. Your handheld/yoke mounted doesn't. You'd get into hot water rapidly using a handheld for navigation in the US.

I've sat in the jumpseat of an IFR commercial flight using enroute GPS, and it was most impressive. Cleared direct from Stansted to Düsseldorf, just like that. I'd like one...

But meanwhile, keep practising the NDB holds, just in case. The CAA might get you on "lacking in airmanship" otherwise!

[bookworm]

<font face="Verdana, Arial, Helvetica" size="2">I've just emerged from reading the US FAR/AIM (sad, but necessary towards the FAA IR). That has some stern warnings about use of GPS, and some very enlightened ones.</font>

It also has some stern warnings about ADF.

"Since ADF receivers do not have a flag to warn the pilot when erroneous bearing information is being displayed, the pilot should continuously monitor the NDB's identification."

We do all do that without fail, don't we? :)

[twistedenginestarter]

bookworm

<font face="Verdana, Arial, Helvetica" size="2">I'm amazed that you regard the three types of approach as similar. They have vastly different user interface </font>.

I was thinking of a vastly similar user interface ie a needle pointing in a direction, but I accept this is not always the case.

A hold starts with you homing in on a set needle direction. Then you set off into no-man's land hoping you will manoeuvre some time later back onto your starting direction. The trick is guessing timings and drifts. Thus largely it doesn't matter which you use.

Well actually you are right. The GPS and VOR give you track, and thus drift. This is very helpful in guessing wind effects.

I once failed my IR because the wind was entirely opposite to forecast so I missed the hold timing by 20 seconds. With GPS or VOR perhaps things would have been very different. http://www.pprune.org/ubb/NonCGI/frown.gif http://www.pprune.org/ubb/NonCGI/frown.gif http://www.pprune.org/ubb/NonCGI/frown.gif

[JuicyLucy]

As this seems to hve turned into a general discussion on GPS use....
One of the problems I have found is it is normally so reliable that people have difficulty in beliving it can, and does, produce inaccurate positions from time to time.
A handheld unit, but fed from a "proper" aircraft aerial, gave some very wrong information around ORTAC last week. It was difficult to ignore the nice (wrong) display and use VOR/ADF instead - even though we both knew the GPS position was suspect !!

[twistedenginestarter]

juice

I am really fascinated how a GPS can be wrong. I can see it might not be able to be right but not how it can be wrong. I'm going to open up a thread on the Tech Board.

;)