ortac wrote:
The DME bias gives more safety margin if not implemented in the GPS, as it reports you as further than charted and hence you will be too high on the approach not too low.
I understand your point. However I would rather put it this way :
“The DME bias gives more altitude for obstacle clearance (and not safety) if not implemented in the GPS, as it reports you as further than charted and hence you will be too high.”
Being too high (~200 / 300 ft) on an approach is not necessary a good thing for safety as it leads to non-stabilized approach.
Obvisously, being too high on a long runway with a SEP in good weather will not lead to an accident.
But I’m not convinced that approaching too high is good for safety in general.
No GPS database vendor (i.e. Jeppesen) is going to generate a database of “DME=0” waypoints.
Who would use it?
In the USA, almost nobody, because they have the proper GPS approaches in most places.
In Europe, commercial users wouldn’t touch it with a 20ft bargepole – totally against their SOPs and probably most of them don’t even have a GPS…
So it would leave just the portion of the GA community which doesn’t have a DME and wants to use a GPS in place of it to fly “DME required” approaches… it would be basically the part of the mainly-SR22 community which flies IFR but whose mission profile exposes it to enough airports which don’t have GPS approaches but need DME. There is no money in this. Due to the high cost of Jepp data, a large chunk of IFR GA uses the free national AIP plates, and those who use Jepps get it mainly from “friends”, often airline pilots. And for certified products (where you cannot share Jepp data) any cost would have to go on top of the already substantial database costs. Even my KLN94 costs me $450/year and that is a lot less than many glass cockpit owners pay.
Garmin don’t produce their IFR/IAP data. It comes from Jepp.
An interesting idea but will never happen.
It would also need some legal foundation to be created. Currently Europe doesn’t allow GPS substitution for DME, and Jepp/Garmin/Etc are hardly going to produce something which has no legal support.
Ortac
I have no problems with the technical aspects of GPS distance, unfortunately Micheal is obsessed with the technical aspects and fails to see the human factors reasons not to use GPS distance substitution. Just one mistake on the VOR/DME approach tothe easterly runway at Larnica will put you 1600 ft low and five miles short of the runway if for your DME substitution you use the LCA NDB rather than the LCA VOR.
If you have a DME in the aircraft and you use it you can’t make this mistake.
If I was the Cypriot authorities and GPS distance substitution was on the cards I would mitigate this risk by re-coding the NDB but as GPS substitution is not yet leagal why would they bother to mitigate a risk that in theory wont happen ?
It is Micheal’s failure to grasp the traps involved in the use of RNAV equipment due to human factors and the inability to undersand that until risks such as I have illustrated at Larnica are mitigated GPS substitution is not safe enough to be exceptable that really bothers me. This sort of attitude if un-corrected would result in a failure of the training course on human factors grounds in the last three airlines I have worked in.
Michael = bad….attitude readjustment required…frontal lobotomy and personality altering drugs prescribed…conformance to the people’s democratic republic of EASAland rules = good….
Or he could just do what every pilot in the US does…
Michael wrote:
Know of any DME approaches where the DME station is a mile off ???
There are examples of ILS-DMEs that are offset to show d=0 at the threshold. Those can be offset by 0,5 NM from the location of the DME station. And there are approaches where multiple nav aids have the same identifier and it is really easy to enter the wrong one into the GPS. Those nav aids can be a lot more than 1 NM apart.
A_and_C wrote:
If I was the Cypriot authorities and GPS distance substitution was on the cards I would mitigate this risk by re-coding the NDB but as GPS substitution is not yet leagal why would they bother to mitigate a risk that in theory wont happen ?
The same risk can happen when programming a FMS. Witness the Cali CFIT accident.
A_and_C wrote:
I have no problems with the technical aspects of GPS distance, unfortunately Micheal is obsessed with the technical aspects and fails to see the human factors reasons not to use GPS distance substitution. Just one mistake on the VOR/DME approach tothe easterly runway at Larnica will put you 1600 ft low and five miles short of the runway if for your DME substitution you use the LCA NDB rather than the LCA VOR.If you have a DME in the aircraft and you use it you can’t make this mistake.
Maybe not THAT mistake, but DME is FAR from bullet proof !
If I was the Cypriot authorities and GPS distance substitution was on the cards I would mitigate this risk by re-coding the NDB but as GPS substitution is not yet leagal why would they bother to mitigate a risk that in theory wont happen ?
It is Micheal’s failure to grasp the traps involved in the use of RNAV equipment due to human factors and the inability to undersand that until risks such as I have illustrated at Larnica are mitigated GPS substitution is not safe enough to be exceptable that really bothers me. This sort of attitude if un-corrected would result in a failure of the training course on human factors grounds in the last three airlines I have worked in.
Boy, talk about making it personal !
Indeed, my OP was to address the technical aspects of GPS for DME fix and I think we can all agree that GPS (particularly WAAS) is superior to DME .
What you seem to fail to consider is that US Pilots have NOT come to misery by substituting GPS for DME !
That, and that alone, pretty much puts to rest any objections or perceived risks you may harbour.
That is unless one can demonstrate that European DME installations are different than in the US and that would rule out the use of GPS for DME fix.
What you seem to fail to consider is that US Pilots have NOT come to misery by substituting GPS for DME !
Michael – do you not see the issue with the lack of “DME=0” waypoints in the GPS database?
There is another factor: if you set a DCT to the airport itself (e.g. DCT EGKA) you get (as I posted above) the distance to the middle of the main runway. That is some 400m away from the MAP. So you would be 400m closer to the airport than you think you are!
But the vast majority of approaches in GA are not flown to minima so people get visual early enough and nobody notices. So everybody is happy, almost nobody gets killed, and everybody wonders why everybody is not allowed to do this.
Very rarely somebody picks a waypoint which really is miles away and then due to more holes in the cheese lining up they get killed. Even then this comes to light only when the GPS didn’t get sufficiently smashed up, and doesn’t melt in a fire, which is probably rare. I did once retrieve the GPS log from a smashed G296… the screen was smashed but the internals still worked, after I re-attached the USB connector. Nobody got killed in that (a Tripacer crash in SW France) one but they all ended up in hospital after getting trapped under a lowering cloudbase and deciding to land on the cloud tops, then falling through to the ground.
Peter wrote:
do you not see the issue with the lack of “DME=0” waypoints in the GPS database?
Have you actually audited the full list of published DME approachs say in the UK for example ?
Further, Is THAT any different than in the US ? Me thinks not, just show me the data , please.
Peter wrote:
Tripacer crash in SW France
I fail to see what this has to do with our DME discussion …
Or is it just to add some drama ?
