GNSS NPA's are dangerous
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Jethro.........
Point 1 - I don't believe anyone is suggesting we rid ourselves of the FAF, just that it be a distance which is referenced to the same point as all the others. Just like in the ILS or DGA scenarios you mentioned. That's the simple difference, they don't have a distance to run to anything other than the one point during the whole of the approach. Thus, one cannot mistakenly identify one segment for another!!!
Point 2 - FAF or no FAF, as a separate waypoint or otherwise..........Limiting altitudes, obstacles and descent points can occur either before, at, or after the FAF. The manner of representation of this Fix is an entirely independent consideration of the step-down issue.
Hope I've cleared that rather than muddied it.
Point 1 - I don't believe anyone is suggesting we rid ourselves of the FAF, just that it be a distance which is referenced to the same point as all the others. Just like in the ILS or DGA scenarios you mentioned. That's the simple difference, they don't have a distance to run to anything other than the one point during the whole of the approach. Thus, one cannot mistakenly identify one segment for another!!!
Point 2 - FAF or no FAF, as a separate waypoint or otherwise..........Limiting altitudes, obstacles and descent points can occur either before, at, or after the FAF. The manner of representation of this Fix is an entirely independent consideration of the step-down issue.
Hope I've cleared that rather than muddied it.
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In response to APMR's comments there is no major technical reason why a GPS box couldn't give distance to MAPt. However, unfortunately these issues go back to the start of the product development cycle and require changes to international and industry standards to resolve. Mind you, that is not to say that making the changes would not be a worthwhile endeavour.
Many of the problems go back to DO-208 the industry standard for aviation GPS receivers. It is an engineers paradise, contains 214 pages of acronyms, test procedures and equations of which 1.25 pages are dedicated to 'operational characteristics' - in other words how the avionics should interface to the pilot.
Neither the FAA/EASA Technical Standard Order (TSO-C129) or the airworthiness requirements (e.g. FAA AC-20-138) required a GPS box to provide anything other than distance to the next waypoint to the pilot. Hence, when the manufacturers have produced their equipment they have complied with the standard. Also any assumptions made by IAP designers are based upon the functional performance outlined in the technical standards which are then reflected in PANS-OPS.
The problem is that even if we go back to sort out the equipment standards there will still be kit around for a long time that only displays distance to next waypoint. So what do you PPruners think we should do to make the best of the situation? In the Australian research mentioned above the specific problems related to workload/confusion seem to be:
1. No flight deck presentation of distance to MAPt (from the GPS),
2. Too many waypoints on the approach too close together with inconsistent leg lengths,
3. Presentation/interpretation of the charts themselves.
Given that (without investment in additional airfield infrastructure - e.g. a DME) the first may take a while to resolve how best should we address the latter 2 points in the IAP design? Also in the opinion of the PPruners would solving 2 & 3 be enough to provide requisite safety levels?
Apologies for the waffling post, but this is something of real interest right now.
Cheers, NM.
PS. As an aside I have sat through and participated in the international standardisation of these units for a number of years and its only recently that I have heard any mention of this distance to waypoint issue being a problem. There was flight crew participation in the standardisation process (albeit limited). I'm not saying that it isn't an issue - because it clearly is, I'm just wondering why no one spotted it before and could it be related specifically to the Australian IAP design?
Many of the problems go back to DO-208 the industry standard for aviation GPS receivers. It is an engineers paradise, contains 214 pages of acronyms, test procedures and equations of which 1.25 pages are dedicated to 'operational characteristics' - in other words how the avionics should interface to the pilot.
Neither the FAA/EASA Technical Standard Order (TSO-C129) or the airworthiness requirements (e.g. FAA AC-20-138) required a GPS box to provide anything other than distance to the next waypoint to the pilot. Hence, when the manufacturers have produced their equipment they have complied with the standard. Also any assumptions made by IAP designers are based upon the functional performance outlined in the technical standards which are then reflected in PANS-OPS.The problem is that even if we go back to sort out the equipment standards there will still be kit around for a long time that only displays distance to next waypoint. So what do you PPruners think we should do to make the best of the situation? In the Australian research mentioned above the specific problems related to workload/confusion seem to be:
1. No flight deck presentation of distance to MAPt (from the GPS),
2. Too many waypoints on the approach too close together with inconsistent leg lengths,
3. Presentation/interpretation of the charts themselves.
Given that (without investment in additional airfield infrastructure - e.g. a DME) the first may take a while to resolve how best should we address the latter 2 points in the IAP design? Also in the opinion of the PPruners would solving 2 & 3 be enough to provide requisite safety levels?
Apologies for the waffling post, but this is something of real interest right now.
Cheers, NM.
PS. As an aside I have sat through and participated in the international standardisation of these units for a number of years and its only recently that I have heard any mention of this distance to waypoint issue being a problem. There was flight crew participation in the standardisation process (albeit limited). I'm not saying that it isn't an issue - because it clearly is, I'm just wondering why no one spotted it before and could it be related specifically to the Australian IAP design?
Last edited by NavMonkey; 7th Oct 2006 at 10:31. Reason: Why do I never spot the typos in preview mode...?!
Grandpa Aerotart
Surely a programming and database update would resolve the hardware issues in any IFR TSO compliant GPS?
It would then simply be a case of a comprehensive reissue of the required IAL plates sans the Foxtrot waypoint.
The one step of removing the Foxtrot waypoint would bring GPS NPA approaches in line with every other IAL procedure...all of which, in the final descent phase, are referenced to a single point in space, a MAP.
For a GPS which is positioned within the radio stack a remote reading display would be required, as is the case now. The GPS signal is coupled to the HSI/CDI, as is now the case, and above the ADI is a small display with waypoint name and distance to it, as is now the case. On the approach plate would be a table with distance/altitude AND a profile which represents that table. For instance the profile may be 3xGPS distance + 100'= profile altitude.
The PIC has now all the information required to fly a safe final approach...he tracks the CDI the way he would for an ILS, either manually or coupled, and simply looks at the distance to the named MAPt in the window a few cm above his ADI as says to himself "3x6+100' = 1900'...on profile".
3x5+100=1600'..50' high (adjust ROD slightly)
3x4+100=1300'...on profile (adjust ROD slightly)
3x3=1000' on profile, gear down.
3x2=700'..approaching minima.
3x1=400' level..MAPt, not visual going around.
And his/her eyes never leave the instruments until he/she looks for visual reference, his scan and SA are maintained.
As it currently stands he is required to be looking at the chart constantly and comparing his altitude and distance from 'a' waypoint..."Hmm 3 miles from F waypoint (which is probably 8nm from the MAPt waypoint) and I should be..where isn it...ok 2500'..ok now 1nm I should be 1800'...now 4nm from the next waypoint I should be..umm...oh 1300'."
In the first example the PIC has no requirement to reference the approach plate at all after briefing and setting up the navaids in the cruise. The way it is at present he must constantly reference the approach plate, during the most critical phase of flight, to have any chance of remaining situationally aware...when he should just be flying the aeroplane.
It would then simply be a case of a comprehensive reissue of the required IAL plates sans the Foxtrot waypoint.
The one step of removing the Foxtrot waypoint would bring GPS NPA approaches in line with every other IAL procedure...all of which, in the final descent phase, are referenced to a single point in space, a MAP.
For a GPS which is positioned within the radio stack a remote reading display would be required, as is the case now. The GPS signal is coupled to the HSI/CDI, as is now the case, and above the ADI is a small display with waypoint name and distance to it, as is now the case. On the approach plate would be a table with distance/altitude AND a profile which represents that table. For instance the profile may be 3xGPS distance + 100'= profile altitude.
The PIC has now all the information required to fly a safe final approach...he tracks the CDI the way he would for an ILS, either manually or coupled, and simply looks at the distance to the named MAPt in the window a few cm above his ADI as says to himself "3x6+100' = 1900'...on profile".
3x5+100=1600'..50' high (adjust ROD slightly)
3x4+100=1300'...on profile (adjust ROD slightly)
3x3=1000' on profile, gear down.
3x2=700'..approaching minima.
3x1=400' level..MAPt, not visual going around.
And his/her eyes never leave the instruments until he/she looks for visual reference, his scan and SA are maintained.
As it currently stands he is required to be looking at the chart constantly and comparing his altitude and distance from 'a' waypoint..."Hmm 3 miles from F waypoint (which is probably 8nm from the MAPt waypoint) and I should be..where isn it...ok 2500'..ok now 1nm I should be 1800'...now 4nm from the next waypoint I should be..umm...oh 1300'."
In the first example the PIC has no requirement to reference the approach plate at all after briefing and setting up the navaids in the cruise. The way it is at present he must constantly reference the approach plate, during the most critical phase of flight, to have any chance of remaining situationally aware...when he should just be flying the aeroplane.
Last edited by Chimbu chuckles; 7th Oct 2006 at 11:47.
Augmentation
Are there any USA counterparts reading this thread that may be able to comment on LPV approaches used in the US with regard to WAAS augmentation capability? This then allows a glideslope indicator to be used for vertical guidance and has in fact lead to lower minimums throughout the US.
I believe AirServices have been considering for some time this method, but are undecided about whether to use the US, Japanese or Euro's augmentation system.
This has got to be a much safer system and we can only hope that the procrastination ends before another tragedy results.
JT
I believe AirServices have been considering for some time this method, but are undecided about whether to use the US, Japanese or Euro's augmentation system.
This has got to be a much safer system and we can only hope that the procrastination ends before another tragedy results.
JT
I'm not sure that the Dist-to-next-waypoint issue is really a newly recognised problem. I recall when GPS NPA's were first introduced in Oz all the guidance material implicitly recognised the problem by emphasising the waypoint distance difference.
Perhaps back then it wasn't realised just how much it's at odds with convention?
Perhaps back then it wasn't realised just how much it's at odds with convention?
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If there isn’t something wrong with the way GPS NPA approaches in Australia are designed then can someone please tell me why there is a ban at my airline (and I assume others) doing such an approach in Airbus aircraft (not sure about Boeing) using “Managed” vertical guidance. This ban is world wide but the problem lies in the design of the approaches in Australia. I have seen one demonstrated in the sim for BNE rwy 19 and the bl**dy thing tries to land you several miles short in the water. I believe there are many other airports in Australia with the same problem. So far no other airports anywhere else in the world have been identified with this same problem.
The ARINC424 standard states where the MAPt is not coincident with the RWY THR then a calculated xing ht must be inserted at the MAPt. Honeywell FMCs don't do this! Jeppesen have confirmed that they have coded the procedure in accordance with the ARINC standard.
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I agree Foxtrot is a crock. OzExPat blames the manufacturers for not wanting to/not able to remove Foxtrot because of scaling issues but I simply don't understand that.
Now that these approaches have allegedly killed more people than an NDB or VOR for years, it's about time CASA changed the design standard in the light of better technology.
If I understand it, CASA was the world leader in GPS NPA design and the concept is great. However, the waypoint at 5nm was a mistake IMO and that should be designed out post-haste.
Now that these approaches have allegedly killed more people than an NDB or VOR for years, it's about time CASA changed the design standard in the light of better technology.
If I understand it, CASA was the world leader in GPS NPA design and the concept is great. However, the waypoint at 5nm was a mistake IMO and that should be designed out post-haste.
although i personally don't have a problem with the concept of distance to next wpt, i can understand that some might, and would prefer a distance to THR [not MAPt as this can be up to 3km fm THR].
what you are looking for is a presentation which will allow you to do some simple mental math to improve your situational awareness. A laudable concept, lord know when ur bouncing around SP IFR on a dark stormy night you don't want to add complexity to what is a difficult time at best.
this does not equate with the REQUIREMENTS of the procedure design to track you from one waypoint to the next [this is what a GPS receiver does - from the manufacturer] whilst keeping you clear of terrain [what the procedure designer does].
your statements are futile. unless the US military amend their specification, the manufacturers won't change their software/hardware, and procedure designers can't change procedure steps.
if you think there is a way to change the procedure plate presentation such that you will be better able to use that information AS IT RELATES TO THE WAY THE DATA IS PRESENTED ON THE GPS UNIT {this bit can't be changed without telling the USM} then, by all means, talk to CASA.
this means the presentation on the GPS won't change as it is not controlled by AsA nor CASA. the procedure plate, either AsA or Jepp version, can be changed. if you reckon there can be an improvement, let someone who can do something about that know. else stop persisting with ur drivel
read "stuffups by Honeywell/Jeppesen". I wonder when they will ever get their act together. Considering millions of people the world over are putting their lives in the hands of their product every day, it's a wonder they can't do a better job (or the regulator doesn't jump on them).
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GPS NPAs had so much promise so it is a great shame they have turned out this way. But, all is not lost - the deficiencies can be rectified.
I am a professional pilot (not GPS NPA endorsed) and also a software developer. Back in 1992, I had to write a GPS based navigation system for a survey company. The survey "runs" consisted of up to a dozen waypoints that were roughly aligned.
Before the software even flew, it was obvious to all of us that the crew, once established on the run, were not interested in the intermediate waypoints - they only wanted to know the distance to the final waypoint.
So, I altered the software to the effect that the intermediate waypoints were effectively hidden. And, if the track from one segment to another changed too much (requiring a significant turn), extra waypoints could be inserted on either side of the transition so as to "smooth out" the change from segment to segment.
The crew had only an across-track display and a distance to run (to the final waypoint of the run). If we had wanted to, we could have easily added turn guidance info for those moments when transitioning from one segment to another.
All very easy. The end result, for the pilot, was one apparent segment that would occasionally change track slightly. We could have flown perfect figure 8's if we had wanted - all as one apparent segment.
So, don't let anyone tell you that the GPS NPAs we have today must work the way they do.
If I had designed them, the pilot would see only 2 waypoints - the IAF and the MAP. Upon activating the approach, the GPS would guide him to the IAF. After passing the IAF, the guidance would then be to the MAP, via several (invisible) intermediate points, with the displayed distance being the track miles to the MAP. The FAF would just be a published distance from the MAP.
To avoid stepped descents and limiting altitudes, vertical guidance (via a glideslope like indication) would be provided and the descent path would be a constant angle. Tricky terrain around the airport would be accommodated via curving approaches. For altimeter check purposes, the altitude the aircraft should be at would be continuously updated and displayed.
Flying one would feel like flying an ILS that changes heading occasionally.
I am a professional pilot (not GPS NPA endorsed) and also a software developer. Back in 1992, I had to write a GPS based navigation system for a survey company. The survey "runs" consisted of up to a dozen waypoints that were roughly aligned.
Before the software even flew, it was obvious to all of us that the crew, once established on the run, were not interested in the intermediate waypoints - they only wanted to know the distance to the final waypoint.
So, I altered the software to the effect that the intermediate waypoints were effectively hidden. And, if the track from one segment to another changed too much (requiring a significant turn), extra waypoints could be inserted on either side of the transition so as to "smooth out" the change from segment to segment.
The crew had only an across-track display and a distance to run (to the final waypoint of the run). If we had wanted to, we could have easily added turn guidance info for those moments when transitioning from one segment to another.
All very easy. The end result, for the pilot, was one apparent segment that would occasionally change track slightly. We could have flown perfect figure 8's if we had wanted - all as one apparent segment.
So, don't let anyone tell you that the GPS NPAs we have today must work the way they do.
If I had designed them, the pilot would see only 2 waypoints - the IAF and the MAP. Upon activating the approach, the GPS would guide him to the IAF. After passing the IAF, the guidance would then be to the MAP, via several (invisible) intermediate points, with the displayed distance being the track miles to the MAP. The FAF would just be a published distance from the MAP.
To avoid stepped descents and limiting altitudes, vertical guidance (via a glideslope like indication) would be provided and the descent path would be a constant angle. Tricky terrain around the airport would be accommodated via curving approaches. For altimeter check purposes, the altitude the aircraft should be at would be continuously updated and displayed.
Flying one would feel like flying an ILS that changes heading occasionally.
however i'll tell you that RNAV (GNSS) [aka GPS NPAs] do have to be designed the way they are currently.
whatever programming you have done was not done for any of the current certified RNAV receivers [GPS or otherwise].
as i've stated in other posts today, the US military gave a spec to which manufacturers created their receivers. the procedures are then just following the MINIMUM spec available as TSO129C. ICAO spelt out how that is done and your regulator will insist how that is implemented.
if there had been input in the late '70s when the spec was created, maybe things would have been different. hindsight is wonderful!
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Hot buoy, if you are doing any other approach with a FAF, I agree its a requirement to know where it is and to track over it. You just use a DME distance or a Marker or whatever to give you its position relative to the MAPt.
OK, I new someone would bring this up. Whatever the manufacturer says, whatever the procedure designer wants, whatever the regulator requires, whatever the tea lady prefers....etc etc.
I'll keep it simple...As a pilot of a multi-crew RPT aircraft, regularly conducting GPS NPAs into various airports, in various weather conditions day and night...
In my opinion, they are dangerous - they need to be fixed now.
I don't give a flying f#$% what it takes, just fix it now.
Not later, now.
OK, I new someone would bring this up. Whatever the manufacturer says, whatever the procedure designer wants, whatever the regulator requires, whatever the tea lady prefers....etc etc.
I'll keep it simple...As a pilot of a multi-crew RPT aircraft, regularly conducting GPS NPAs into various airports, in various weather conditions day and night...
In my opinion, they are dangerous - they need to be fixed now.
I don't give a flying f#$% what it takes, just fix it now.
Not later, now.
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I agree!
Are you for real? I get the impression that those in the "technically impossible, too expensive" camp have given up on this one. All the passengers and crew who may have to eat dirt as a direct result of this hazard probably would beg to differ.
Are you for real? I get the impression that those in the "technically impossible, too expensive" camp have given up on this one. All the passengers and crew who may have to eat dirt as a direct result of this hazard probably would beg to differ.
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The RTCA docs are developed by (usually large) committees composed of airframers, avionics manufacturers, ANSP's, CAA's and others from around the world.
The only military connection in any of this is that GPS is being used and the performance of the SPS element of the GPS service has been specified by the US DoD. All of the aviation receiver functionality be it the HMI, how integrity is provided, how to generate a nav solution, how to generate guidance for an RNAV route are the product of the RTCA committees, not DoD.
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I haven't had any bad experience with them in many years of extensive exposure to them, in all climates.
Situational awareness AND good multi crew support is the key.
Can't comment on jet software (Airbus)...suffice to say Boeings BDFW is good (Box t'Does Fuggin Wonders).
Requests previously did go in to modify the Jepp plates, re distance to MAP not next WPt and graphic MSA floors for better comprehension (Eastern/QF, I believe)... many have been adjusted.
Found them safe and no probs with them myself but interesting to read.
Situational awareness AND good multi crew support is the key.
Can't comment on jet software (Airbus)...suffice to say Boeings BDFW is good (Box t'Does Fuggin Wonders).
Requests previously did go in to modify the Jepp plates, re distance to MAP not next WPt and graphic MSA floors for better comprehension (Eastern/QF, I believe)... many have been adjusted.
Found them safe and no probs with them myself but interesting to read.
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This will become a hot topic in the UK next year
UK CAA are currently conducting a GNSS NPA trial which was due to end this month, but I hear is to continue to the end of the year.
I flew a couple a while back and was thrown by the Step Down Fixes (SDW) and tempo lost spatial awareness.
I agree that the presentation of distance to go from GPS and conventional RNAV is an issue that needs to be addressed.
What ever the answer is it should be adopted world wide. Over to you ICAO
Sir George Cayley
ps Funny in here. All the alcohol rushes to me 'ed
I flew a couple a while back and was thrown by the Step Down Fixes (SDW) and tempo lost spatial awareness.
I agree that the presentation of distance to go from GPS and conventional RNAV is an issue that needs to be addressed.
What ever the answer is it should be adopted world wide. Over to you ICAO
Sir George Cayley
ps Funny in here. All the alcohol rushes to me 'ed
Last edited by Sir George Cayley; 9th Oct 2006 at 18:46.
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Good thread, this is something I've had a problem with since I started using this type of approach.
The main point seems to be that GPS distance to next approach waypoint can be confusing.
The fix seems obvious: Publish both distances. Not ideal of course, but you could make use of the distance to MAPt and use the distance to next waypoint to crosscheck - this would stop any waypoint confusion.
Most GPS units are able to display total distance to each waypoint, and this page is only required until you reach the final approach fix, where the distance becomes intuitive.
The main point seems to be that GPS distance to next approach waypoint can be confusing.
The fix seems obvious: Publish both distances. Not ideal of course, but you could make use of the distance to MAPt and use the distance to next waypoint to crosscheck - this would stop any waypoint confusion.
Most GPS units are able to display total distance to each waypoint, and this page is only required until you reach the final approach fix, where the distance becomes intuitive.
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Altitude awareness?
And while you are concentrating on all this, it is easy to lose altitude awareness. I reckon this sort of thing has killed a few already. So far, only in small numbers.
The technology is there to fix it.
The technology is there to fix it.
Hot Boy,
You can call it what you like mate, the fact is that people are having problems with GPS NPAs because of the difficulty caused by Foxtrot and it is likely that the design contributed to the deaths of 19 people. And yes, you'll be pleased to know that I have had quite a lot of success in forcing Jepp/Honeywell to change their database programming, which just goes to make the whole situation more pathetic: it could be done properly but it wasn't.
As you know I have said before (how many Prune guises do you have?), the box doesn't give two hoots about where the waypoints are for tracking or mode changes. One of our boxes starts scaling down to APPR 2nm before it gets to Foxtrot so it's pretty obvious in doesn't need to fly over a waypoint to start doing something different.
IF your theory about the design criteria is correct (and NavMonkey's answer above casts doubt on that) then the design criteria, allowing one waypoint at ~10nm, should be changed and the Foxtrot "point" should become a distance from Mike (as it is with every other non-precision approach). I simply do not accept that the technology to do this cheaply doesn't exist. NavMonkey might have to redraw all the approach charts, but that'll give him something to do!
stop persisting with ur drivel
As you know I have said before (how many Prune guises do you have?), the box doesn't give two hoots about where the waypoints are for tracking or mode changes. One of our boxes starts scaling down to APPR 2nm before it gets to Foxtrot so it's pretty obvious in doesn't need to fly over a waypoint to start doing something different.
IF your theory about the design criteria is correct (and NavMonkey's answer above casts doubt on that) then the design criteria, allowing one waypoint at ~10nm, should be changed and the Foxtrot "point" should become a distance from Mike (as it is with every other non-precision approach). I simply do not accept that the technology to do this cheaply doesn't exist. NavMonkey might have to redraw all the approach charts, but that'll give him something to do!
Last edited by Capn Bloggs; 10th Oct 2006 at 11:24. Reason: correcting doubled text
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Bloggs,
I'm with you 2,000% on this one!!
Loss of altitude awareness as you struggle through the segments is a major problem. Not only for a newbie [to this approach], but even a reputable [?] operator at my home GA port; the EGPWS doesn't work in the landing configuration!
G'day
I'm with you 2,000% on this one!!
Loss of altitude awareness as you struggle through the segments is a major problem. Not only for a newbie [to this approach], but even a reputable [?] operator at my home GA port; the EGPWS doesn't work in the landing configuration!
G'day