GPS vs NDB (does NDB really meet RNP)?
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GPS vs NDB (does NDB really meet RNP)?
I was reading a recent CAA publication which outlined the RNP for approval as a primary approach aid - and all of the reasons why the current GPS system does not meet these requirements. After monitoring the NDB 20 approach into Shoreham (with 35 knots declining to 20 on the surface from 280 and very gusty) on the GNS430 I thought - does this NDB approach meet the RNP requirements.
With the impact of shore line and mountain refraction, random swings from some nearby CBs and other interference and reasonably complex pilot interpretation to reflect the shifting winds (at least complex compared to the GPS or a VOR) does this system really deliver the RNP standards (and certainly is the GPS less reliable)
Any thoughts on the question.
With the impact of shore line and mountain refraction, random swings from some nearby CBs and other interference and reasonably complex pilot interpretation to reflect the shifting winds (at least complex compared to the GPS or a VOR) does this system really deliver the RNP standards (and certainly is the GPS less reliable)
Any thoughts on the question.
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The main reason the CAA don't like GPS, is that they don't have any direct control over it.
GPS is a 1000X more useful than an NDB as long as the Yanks don't mess with the signal!
GPS is a 1000X more useful than an NDB as long as the Yanks don't mess with the signal!
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The Shoreham 20 NDB/DME AIP is atrocious in the NDB error; it is a good 20 degrees out at 6D, straightening out by the time one gets to about 3D.
SAS
I am not sure that is the reason they don't like it. They don't like all sorts of things. Look at the Cirrus BRS - there is no rational argument against it, or against any other feature which might save lives. I think one might get an interesting angle on it if one looked at the sort of aircraft which the PPL holders working at the CAA GA Dept fly themselves...
SAS
I am not sure that is the reason they don't like it. They don't like all sorts of things. Look at the Cirrus BRS - there is no rational argument against it, or against any other feature which might save lives. I think one might get an interesting angle on it if one looked at the sort of aircraft which the PPL holders working at the CAA GA Dept fly themselves...
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An NDB meets the RNP for an NDB be it used to define the centerline of an airway or as an approach aid.
When constructing the approach procedure, allowance is made for the inaccuracies of the NDB and the obstacle clearance heights reflect the errors inherent in the system.
GPS can be more accurate than NDB and if an approach procedure was to be constructed, it's minima would reflect that accuracy.
However, when completing the NDB approach everyone constantly monitors the ident because there is no warning of failure. GPS does not have any ident or warning of failure that the CAA find as acceptable for instrument approaches. Thus there are not any GPS approaches yet.
The CAA is not overly worried that the Yanks can turn off the Navstar system at any time it chooses because the owner of the NDB at Shoreham is similarly entitled to act with their property.
The CAA is worried that errors and jamming can affect the Navstar system in unpredicatable and possibly unexpected ways possibly without any warning to the user. It is illegal for the owner of the NDB at Shoreham to mess with the signal from the NDB.
What are people using to assess how well the NDB is showing the approach centerline?
If it is the runway centerline then remember that the NDB is not on the runway and thus an angular difference exists between the runway centerline and the NDB approach. This lateral displacement gets further away from the runway centerline with distance. Remember that as long as it is within 30 degrees of the runway it counts as a straight in approach.
Also remember that any error is the result of the total system error i.e. the receiver error and the indicated error as well as pilot error.
Insted of worrying about coastal refraction which is not a significat factor on the 20 approach, pilots should remember the effects of quadrantal error especially with a strong westerly wind.
There is however one inherent system failure in the UK - NDBs are not reguluarly flight checked in the same way as other approach aids.
Regards,
DFC
When constructing the approach procedure, allowance is made for the inaccuracies of the NDB and the obstacle clearance heights reflect the errors inherent in the system.
GPS can be more accurate than NDB and if an approach procedure was to be constructed, it's minima would reflect that accuracy.
However, when completing the NDB approach everyone constantly monitors the ident because there is no warning of failure. GPS does not have any ident or warning of failure that the CAA find as acceptable for instrument approaches. Thus there are not any GPS approaches yet.
The CAA is not overly worried that the Yanks can turn off the Navstar system at any time it chooses because the owner of the NDB at Shoreham is similarly entitled to act with their property.
The CAA is worried that errors and jamming can affect the Navstar system in unpredicatable and possibly unexpected ways possibly without any warning to the user. It is illegal for the owner of the NDB at Shoreham to mess with the signal from the NDB.
What are people using to assess how well the NDB is showing the approach centerline?
If it is the runway centerline then remember that the NDB is not on the runway and thus an angular difference exists between the runway centerline and the NDB approach. This lateral displacement gets further away from the runway centerline with distance. Remember that as long as it is within 30 degrees of the runway it counts as a straight in approach.
Also remember that any error is the result of the total system error i.e. the receiver error and the indicated error as well as pilot error.
Insted of worrying about coastal refraction which is not a significat factor on the 20 approach, pilots should remember the effects of quadrantal error especially with a strong westerly wind.
There is however one inherent system failure in the UK - NDBs are not reguluarly flight checked in the same way as other approach aids.
Regards,
DFC
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I just love my ADF, no matter where you are in the world you can always get the BBC
I did hear that some people still use them to find airports, not sure if it's true though.
Tony
I did hear that some people still use them to find airports, not sure if it's true though.
Tony
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DFC,
Approved GPSs have RAIM warning, which is akin to the warning flag on your VOR/ILS display.
That is one of the key differences between handhelds and installed approved GPSs.
You can read up more about this here.
The CAA does approve sets for en-route navigation but not approaches, so not sure if they are too worried about the technological side of the matter.
Could it be the time money and effort required to get the GPS approaches sorted.
The UK system does not allow IAPs without an approach controller. These creatures are fairly thinly spread over the places that do have IAPs. Places that could be most interested in GPS approaches are those that don't currently have any approach and may be unlikely be able to afford the bells and whistles required to set up the entire entourage for an IAP.
I suspect there is more to it than meets the eye from our perspective.
FD
Approved GPSs have RAIM warning, which is akin to the warning flag on your VOR/ILS display.
That is one of the key differences between handhelds and installed approved GPSs.
You can read up more about this here.
The CAA does approve sets for en-route navigation but not approaches, so not sure if they are too worried about the technological side of the matter.
Could it be the time money and effort required to get the GPS approaches sorted.
The UK system does not allow IAPs without an approach controller. These creatures are fairly thinly spread over the places that do have IAPs. Places that could be most interested in GPS approaches are those that don't currently have any approach and may be unlikely be able to afford the bells and whistles required to set up the entire entourage for an IAP.
I suspect there is more to it than meets the eye from our perspective.
FD
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My, my I do get a charge out of these discussions. 
Maybe we should discuss the pros and cons of the horseless carriage and the reliability of transport by horse?
Anyhow gang I still get a kick reading all this hand wringing about GPS.
Cheers....
Chuck
Maybe we should discuss the pros and cons of the horseless carriage and the reliability of transport by horse?
Anyhow gang I still get a kick reading all this hand wringing about GPS.
Cheers....
Chuck
PPRuNe Handmaiden
GPS NPA approaches are quite common in Australia. Approach charts are designed and issued.
The GPS must be a fixed mounted IFR approved unit with RAIM and an updatable (and current) database. The pilot must also be checked out on NPA's as well.
The GPS must be a fixed mounted IFR approved unit with RAIM and an updatable (and current) database. The pilot must also be checked out on NPA's as well.
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DFC
Is your post really the official view of the CAA? Do you work there?
"However, when completing the NDB approach everyone constantly monitors the ident because there is no warning of failure"
Actually, receiving the audio ident means nothing, zero, zilch, nowt, nothing whatever about whether the NDB is indicating anything meaningful whatsoever. All it tells you is that the the part of the circuitry that receives and demodulates the AM ident works, and the unit is tuned to the right frequency.
Same incidentally applies to a VOR. I've flown with dead VOR receivers (in "VFR" school aircraft) which idented just fine.
Whereas a GPS will detect if it isn't getting a solution from the received signals. There is also RAIM.
If what you wrote is really the official view of the CAA, they need some education on how radio works
It is true GPS can be jammed. Then one would not do that approach. Same with DME packing up; one cannot do a "DME mandatory" IAP. Any gizmo can pack up, anytime. Loads of GA planes have duff DMEs or duff ADFs. So instrument flying should be banned unless one has two of everything.
Finally, does the CAA know something the FAA don't?
Is your post really the official view of the CAA? Do you work there?
"However, when completing the NDB approach everyone constantly monitors the ident because there is no warning of failure"
Actually, receiving the audio ident means nothing, zero, zilch, nowt, nothing whatever about whether the NDB is indicating anything meaningful whatsoever. All it tells you is that the the part of the circuitry that receives and demodulates the AM ident works, and the unit is tuned to the right frequency.
Same incidentally applies to a VOR. I've flown with dead VOR receivers (in "VFR" school aircraft) which idented just fine.
Whereas a GPS will detect if it isn't getting a solution from the received signals. There is also RAIM.
If what you wrote is really the official view of the CAA, they need some education on how radio works
It is true GPS can be jammed. Then one would not do that approach. Same with DME packing up; one cannot do a "DME mandatory" IAP. Any gizmo can pack up, anytime. Loads of GA planes have duff DMEs or duff ADFs. So instrument flying should be banned unless one has two of everything.
Finally, does the CAA know something the FAA don't?
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DFC you wrote -
"An NDB meets the RNP for an NDB be it used to define the centerline of an airway or as an approach aid."
The question that was in my mind was - does the actual accuracy, reliability, precision, time to alert on various failure modes (i.e. the RNP) for an NDB achieve the level the CAA argue GPS (with RAIM) would need to achieve (but in the CAA view doesn't) to be used as a primary non-precision approach device.
"An NDB meets the RNP for an NDB be it used to define the centerline of an airway or as an approach aid."
The question that was in my mind was - does the actual accuracy, reliability, precision, time to alert on various failure modes (i.e. the RNP) for an NDB achieve the level the CAA argue GPS (with RAIM) would need to achieve (but in the CAA view doesn't) to be used as a primary non-precision approach device.
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Personally, when doing an NDB approach I always tend to use the GPS more than the NDB. I find it a far simpler and more accurate method than a needle on an RMI which then requires you to move your view to cross reference the DME.
This isn't on a bug smasher, this in two crew airline ops and seems to be standard practice amongst the crews in the company.
I've heard some pretty harrowing stories about nav aids that ident properly and seem to be working, but in reality are far from fully functional. The worst concerns an A320 of Bmed going into somewhere in Africa where the VOR radials themselves were rotating slowly causing the EGPWS to believe it was in a different place (no GPS input). The a/c narrowly missed piling into a ridge line (by about 70' I believe) only due to the dilligence of the crew.
How did Bmed respond? By putting a GPS card into the EGPWS.
Says it all really. If the technology is there, use it.
This isn't on a bug smasher, this in two crew airline ops and seems to be standard practice amongst the crews in the company.
I've heard some pretty harrowing stories about nav aids that ident properly and seem to be working, but in reality are far from fully functional. The worst concerns an A320 of Bmed going into somewhere in Africa where the VOR radials themselves were rotating slowly causing the EGPWS to believe it was in a different place (no GPS input). The a/c narrowly missed piling into a ridge line (by about 70' I believe) only due to the dilligence of the crew.
How did Bmed respond? By putting a GPS card into the EGPWS.
Says it all really. If the technology is there, use it.
Last edited by Say again s l o w l y; 11th Jul 2004 at 21:16.
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I maybe getting cynical, but...
I cannot help but think that the whole GPS Nav/Approach issue in Europe has to do with the fact that its american and free...
I am willing to bet that as soon as the European version (Galileo?) becomes operational it will be approved overnight...but then we will have to pay through the nose for it too......
But then I am getting really cynical the more I see how Europe operates...
Regards, SD.
I am willing to bet that as soon as the European version (Galileo?) becomes operational it will be approved overnight...but then we will have to pay through the nose for it too......
But then I am getting really cynical the more I see how Europe operates...
Regards, SD.
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Here is a picture of the 02 approach at Shoreham:
I have flown that approach at night, with the needle bang centred on the RMI, and popped out of cloud over the coast about 2nm West of the airfield. That looks to be about 35deg off course.
Shoreham is a particularly bad example, because of the combination of night effect and refraction, but give me GPS every time!
I have flown that approach at night, with the needle bang centred on the RMI, and popped out of cloud over the coast about 2nm West of the airfield. That looks to be about 35deg off course.
Shoreham is a particularly bad example, because of the combination of night effect and refraction, but give me GPS every time!
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I am unfortuneatley not in the exalted ranks of the IR/IMC/Night brigade so cannot comment from that point of view. However I am sorry to say that I class Politicians, Salesmen and government agencies and experts in the same class, the truth modified by all the gigary pokery that has to be applied because we the people are "just to ignorant to understand or use our brains".
Dare I mention Iraq, oops!
Mike
Dare I mention Iraq, oops!
Mike
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I find the 02 IAP not as bad; usually I end up east of the track but not too much. Tracking an inbound of 035 on the RMI would work a lot better. One would expect a lot of coastal effect on that one, however.
It is the 20 IAP which is potentially worse because of the terrain.
It is the 20 IAP which is potentially worse because of the terrain.
