View Full Version : GPS APPROACHES
Goldenhawk
1st Apr 2006, 17:57
CAA to Conduct GPS Approach Tests for General Aviation Aircraft
The United Kingdom Civil Aviation Authority (CAA) will test Global Positioning System (GPS) Non-Precision Approaches (NPA) for general aviation aircraft at six UK airports. The six airports include Blackpool, Durham Tees Valley, Exeter, Gloucestershire, Iverness, and Shoreham. UK CAA-licensed pilots, flying UK-registered aircraft, may take part in these tests. The aircraft involved must be fitted with appropriate GPS equipment that has been fully approved in accordance with Aeronautical Information Circular (AIC) yellow 205 for NPA operations. The tests will run from May through October of 2006.
Question: Are any commercial operators currently doing GPS approaches in the UK?
Barndweller
1st Apr 2006, 22:06
Lots! (but none of them are approved!!!!)
helmet fire
1st Apr 2006, 22:56
With almost 10 years of approved GPS NPA (now called GNSS) ops in Australia, I'd have to say: GO FOR IT.
Why did this take so long for the UK?
What are they going to test that hasn't already been done in the last 10 years elsewhere?
Interesting, I've been doing them in Canada-legally- for more than 4 years.
They work really slick especially with an en-route transition to a STAR followed by a RNAV (GPS) approach.
SASless
2nd Apr 2006, 04:21
NIH....Not Invented Here!
It's an American DOD thing you know....:{
Ah Sasless, but if the DoD's GPS system is so reliable, why are the US Coastguard pursuing Loran with such vigour? As I understand it they are planning to use a master timing station to give improved accuracy (claimed to be close to that of GPS). Do they know something that others don't - Loran in Europe is losing popularity (not helped by the Irish never putting up the Loop Head aerial).
The Loran users website indicates that eLoran (the new and improved version of Loran C) is an ideal backup and complement to GNSS - why would you need that if GPS as a standalone is good enough for aviation approaches?
an answer here perhaps -
http://www.loran.org/library/FinalLastPaperEJN2.pdf
tsk tsk - the mighty GPS has weaknesses......shock horror!
Runway GPS approaches.
What location on each runway is specified for a GPS approach and are these locations reliably promulgated anywhere?
Helmet
Aren't they called "RNAV" approaches in Aus??
MILT
I think the answer to your question is that the approach points are promulgated on each chart (missed approach waypoint, flyover waypoint, etc) and these are stored on each GPS datacard.
helmet fire
2nd Apr 2006, 23:57
Oogle, yep, GNSS RNAV approaches. Anything to complicate and change rather than stick by explanative nomenclature. They are a GPS approach that is non-precision, so what was wrong with "GPS NPA"?
Milt: the approaches are not to a specific point on the runway. They are the same as a VOR/DME, or NDB/DME in that they are approaches to a missed approach point that is determined by both azimuth and distance. There is no real difference because it is GPS. As such, they are promulgated in the same way any other approach waypoint is, on the instrument approach chart.
Crab: I dont think anyone is saying it is a standalone 100% reliable capability. Neither is Loran. Or VOR, etc. Each system should be complimented by a backup of some sort, and in the Coast Guard environment that has no ILS and VOR handy as a back up, we are back to Loran. I bet the Coast Guard are no getting rid of the GPS units in their aircraft.
mfriskel
3rd Apr 2006, 00:28
GPS with WAAS is being approved with precision approach minimums in the USofA.
cl12pv2s
4th Apr 2006, 01:38
Incredible!
Only when I left the US, did I realise how far behind a lot of the rest of the world are with their GPS / RNAV development.
(Before anyone jumps, I say this purely as a matter of fact.)
Milt: the approaches are not to a specific point on the runway. They are the same as a VOR/DME, or NDB/DME in that they are approaches to a missed approach point that is determined by both azimuth and distance. There is no real difference because it is GPS. As such, they are promulgated in the same way any other approach waypoint is, on the instrument approach chart.Just for your information:
The first stage of the transition and 'testing' of GPS in the US was called an 'overlay' approach, where the GPS approach was simply overlayed on an existing Non-precision approach.
The next step in the GPS introduction was to have a GPS approach what was not predicated on any existing Navaid at all. - A standalone GPS approach. (After all it's GPS!). This allowed for the basic-T design (and its modifications) to become standard.
http://www.faa.gov/ATpubs/AIM/Chap5/F0504001.gif
Moving on from the Basic-T the Terminal Arrival Area standards was developed. This is a standard for the area surrounding an RNAV approach. It is so beautifully simple that a controller can give a clearance 30nm out and not speak to the arriving aircraft until the FAF. No need for 'waypoint' instructions either as its all on the plate.
The US is now in the process of implementing the VNAV approaches, with the use of WAAS.
No need for VORs or NDBs or any other land-based navaids everr again!
Maybe one day in the future, technology will be available for helicopter pilots to plug in the coordinates of a car crash / rig / heli-skiing drop site / roof top helipad / construction site etc...etc... and 'hey, presto!' the GPS writes a custom 'Point-In-Space' legally approved approach to that point, with appropriate minima etc..etc..
As for the integrity of the system and the Volpe Report stated earlier...yes, there are some drawbacks.. loss of RAIM and possible targeting by terrorist groups.
However, the article mentioned earlier was based heavily on the Volpe Report, which was published in 2001 (I think). This was before GPS technology was well developed, before the were so many satellites, and most importantly, before there were viable alternatives to the US GPS system (Glonass??, Galileo)
With these in mind, I think the GPS concept is the way forward for aviation and world navigation. You'll eventually have receivers that can 'lock' onto any of the systems as necessary, assuring complete navigation all the time.
From a heli pilot's perspective, yes LORAN is a great backup, but it is also susceptible to its own problems, and at the end of the day is predicated on radio technology, and is thus 'line of sight'. It requires expensive ground based stations. So, as a backup (or alongside) GPS yes, as primary navigation system (as the LORANites would love to see)...nah!
cl12pv2s
helmet fire
4th Apr 2006, 04:59
I am not so sure "the rest of the world" is so far behind. We were doing approved helicopter GPS approaches in Australia by 1997, and Terry Summers, a NSW based EMS Captain and Instrument ATO was heavily involved in setting the international standards of the approaches. "A matter of fact" as you would put it.
I note that the USA has settled on the "T" entries, but Australia went for the "Y" entries which I believe are the ICAO standard. The Y entry is essentially the same, but it requires a less than 90 degree turn on to the FAF leg. In addition, that standard has a third IAF 3 odd miles (for helicopters) out from the IF and in line with the finals leg. This creates three possible IAF, each with a maximum of 70 degree turns to join the initial leg.
The real development will be courtesy of a Mr Lappos. This will be when they start certifying GPS approaches to the helicopter capabilities of very slow speed at the missed approach point, all flown coupled. In that area, the USA is far ahead, and it will be some time before it seeps into Australia. But our fingers are crossed.
cl12pv2s
4th Apr 2006, 05:10
Helmet fire,
You're right...
So I'll rephrase...
I was surprised how behind some countries are!
Certainly, Australia and Canada have embraced the potential of GNSS, as the US have.
Interesting about the 'Y' and extra IAF. I would be interested in knowing the reference to this ICAO standard (if you have it).
cl12pv2s
Antoine
4th Apr 2006, 07:49
I'd be curious to know how many GPS NPA are approved in the States and Canada ?
and are new old-style precision approaches still installed, or are all the new helicopter approaches based on GPS now ?
Do you see any future for helicopters with the VOR-DME / ILS system, considering the ease induced by the GPS and GPS-like systems ?
Thanks
Antoine just about every NPA in Canada has a GPS overlay approach as well.
Many remote airports only have GPS approaches.
The RNAV (GPS ) approaches follow the T -standard illustrated in cl12pv2s post.
We still have a large number of NDB approaches. I suspect they won't be around 20 years from now.
Localizer Back-Course appoaches are being phased out-slowly.
The ILS approach- I think- will be around for quite some time; even though it is old technology it's still a fantatastic approach aid.
2nd2none
5th Apr 2006, 01:19
Very Intersting topic, we are designing our own GPS app to hospital helipads here in Alberta, Canada. Not IFR helipads, but day/night VFR pads with PInSA works very well!
2beers
5th Apr 2006, 09:07
GPS is the U.S military version of a GNSS which also gives them full control over it. I can understand if there are many countries that are happier to rely on older technologies over which they have full control.
But a good thing for the rest of the world is that GALILEO will be up and running from 2008, which is much more suited for civilian applications and not controled by the military or a single country. As they say on their website: "A system that both competes with and complements the American GPS system".
One of the features is that it is sending an "integrity message" informing the user immediately of any errors. Nice to have on a future GNSS precision approach to the hover, don't you think?
Interesting reading:
http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm
/2beers
Shawn Coyle
5th Apr 2006, 21:52
2beers:
The US Government has said they would not turn off GPS. It is a utility that is so widely used in the USA and other parts of the world that the effect of turning it off on the civil economy would be pretty large.
They are in fact adding more features to the system to provide better accuracy for civil use, and will continue to support it for many years.
GPS already has integrity features built in - the European system adds many things, but GPS is still quite useful (and will be free - how much are the Europeans going to charge for use???)
Here is an approach I flew recently. I took a picture of the EFIS display[ in MAP MODE]. The EFIS display mirrors the approach plate, making interpretation very easy.
http://img.photobucket.com/albums/v633/jetboxIII/Presentation1.jpg
http://img.photobucket.com/albums/v633/jetboxIII/IMG_0081.jpg
Geoffersincornwall
6th Apr 2006, 04:48
This is an extract from a paper presented by Dave Howson (UK CAA SRG) last October in Montreal.
Use of GPS for Offshore Helicopter Operations - Low Visibility Approaches
Background
Low visibility approaches to offshore platforms are currently based on the use of weather radar for navigation and as a means of detecting obstacles on the approach path. Although it has been used for this purpose for a number of years, weather radar is neither designed nor certificated for such operations. In addition, these operations were identified by the Human Factors Working Group [2] as an area of potential safety improvement. Consequently, UK CAA has been investigating alternative means of conducting these operations. These investigations have focussed on the use of GPS, and have included a series of trials activities and follow-on data analysis exercises which have been reported in CAA Papers 2000/5, 2003/2 and 2003/7 [34, 35, 36]. UK CAA believes that the results of these investigations have demonstrated GPS to have significant potential for use as an offshore approach aid.
Following on from this work, a hazard analysis of the use of GPS for helicopter offshore approaches is being conducted. This exercise has been split into two parts; the first deals with the use of existing North Sea helicopter GPS equipment to enhance the existing weather radar approaches; the second will focus on a GPS-based offshore approach for which new aircraft equipment will be required.
We're working on it.
G
:ok:
Geoffers - the last line means 'we're working on it - but it'll cost you a load more money to comply with the regulations we eventually impose':)
Crab,
No, it is saying that Differential GPS will be required.
However, these approaches will still need some 'device' to establish the obstacle environment - that device is presently the Airborne Radar. What DGPS achieves is to more accurately position the aircraft than with existing nav aids - this will permit the MAP to be closer to the platform; and of course there is the provision of vertical guidance.
One of the continuing issues is the loss of the ability to approach from any direction - once that has to be decided by the software, it will require extensive modification.
Jim
Crab
From USCG NAVCEN report!
“New technology has allowed the Coast Guard to establish centralized control of the continental U.S LORAN-C system at two locations...........It should read “From” two locations.
The posturing from USCG NAVCEN is about empire building. It was a reasonable navaid (when it worked) but its time has come and gone.
170
JimL my post was meant 'tongue in cheek' but is probably correct if what you say is right. Are GPS approaches approved in other countries without the need for Differential GPS (accepting that making an approach to an airport with predetermined obstacle clearance planes is not the same as making an approach to an ostacle like a rig)?
170' - the Loran users organisation (does that make them L-osers) is bigging up the new e-Loran as a complement and/or alternative to GPS and since the USCG seem to fund the LORAN chain in the US they don't seem about to dump it.
Hi Crab,
A number of States have a generic ARA (JAA, FAA, TC) which permits the approach guidance with a number of aids. These used to be NDB or DECCA but overlaying with the GPS is now more usual.
As was said earlier, DGPS will still rely upon the RADAR for clearing the approach and go-around sector as the obstacle environment is complex in offshore operations. Improving the minima depends upon more accurate positioning and vertical guidance.
Practical considerations will determine the outcome of this research - which is being undertaken mainly to legitimise what it presently being done today. The introduction of EGNOS and Galileo will result in WAAS for offshore operations in Europe within a couple of years.
The gap in RADAR cover will also have to be plugged in the near future -this could be achieved also by using satellite facilities; the GOM appear to be ahead of Europe in this - probably because they have a larger hole to plug.
Jim
Crab
I think you could be on the mark with L-osers ;-)
….
It seems obvious to me that the best backup/alternate to GPS- has to be aircraft based…
Otherwise you’re back to square one. With someone having control of a switch somewhere. And we know this switch is not powered with electricity, but by politics.
Creating mirror technologies means there are now multiple switch-keepers to negotiate with.
So the best deal all-round, is something akin to INS/IRS platform technology, with fix updating via all available means such as GPS, vortacs, dme, etc…(already there in RNAV form)
Plus cell phone sites, Remote Satellite Measurement Units, for both arrival and en-route update…Commercial radio stns maybe. (Limitations notwithstanding). Radar …ad infinitum
Plus updating aircraft to aircraft.....(extension of TCAS)
Imagine I’m eastbound at 15West with 96% nav accuracy after crossing the pond (GPS is TU)…Your 4000’ below, westbound after checking Benbecula, where you updated from a RSMU or the VOR and have 99.9 recurring% accuracy…My widget transparently updates from your widget, and the 5 or 6 others in range…
Now extend this to an approach to a rig, where you have a bunch of Boeing/Airbus in LOS…. Speed bird 17 and his friends, are seamlessly updating your position if they have a minimum assured nav accuracy themselves.
The unit’s won’t accept one or two erroneous signals from terrorists, faulty or vandalized ground emitters etc, but (as with old INS technology) will only accept a limited position error update…from its last known position consistent with its INS position
Basically if it receives a signal that doesn’t match the mixed signal info it already possesses, it dumps the erroneous signal. Similar to running in triple mix mode on the old INS system…
All this is notwithstanding the great accuracy of current generation INS/IRS/RNAV as a stand alone system, particularly on the short legs involved in helo ops, where you do a manual position update on each rig or LZ.
I have no idea of the complexity involved, but I imagine a triple doctorate from MIT could probably draw it out on a napkin….;)
I guess time will tell! But I wouldn’t be buying shares in any Loran stock. ...170'
ps...No I can't help out with development costs :hmm:
170,
It is probably correct that the most potent of combinations is that of the GPS and INS - at least for the most critical portion of flight, the instrument approach (where the horizon prevents other signals from being received). The INS - updated by the GPS - would provide the guidance signal; if the GPS signal were to fail, there would be sufficient accuracy left in the system to complete the approach or go-around.
Strange then that these installations are few and far between - which points to cost or technical problems. The only (almost) helicopter which I know that is equipped with one of these is the Bell X-15.
Jim
170' - it sounds great - have it wrapped and sent round...:D
JimL - if DGPS will still require an improved radar to more accurately determine the obstacle environment then why not just improve the radar and get reduced minimas that way? Do the N Sea operators really need to improve their bad weather capability or will the number of times a DGPS approach gets used in anger justify the cost? If the CAA is willing to look at GPS approaches to rigs then why not to airports -those plates shown earlier seem to be standalone and not requiring additional navaids.
Jim
Yes, It's a shame the INS has always been very limited in helo ops.
My exposure was mostly in FW days, with the old Carousel IV followed by the Litton 92. But in long range ops, the accuracy of even this aged equipment was sometimes startling.
I think the a/c to a/c update could be a real boon though...
It's little more than an extension of TCAS and imagine getting updates from a high flying heavy (ies) all the way down to MDA...If we say the LOS @ FL330 is roughly 220nm...It wouldn't be often you'd be out of LOS of someone who is getting constant updates themselves...
Yeah! Tooth fairy stuff;)
170'
oldmanofthesky
8th Apr 2006, 14:11
Goldenhawk (or anyone who knows the answer), can you tell me where you found the info regarding GPS Approach Trials, please?
As someone who operates an IFR helicopter from one of these airfields I would like to find out more. Thanks.
Crab,
I may have confused you and others by mixing text on two different RADARs; with regard to ARA, I was only commenting on the airborne (weather) RADAR.
When flying the approach with the NDB/ADF, weather RADAR is used for ranging as well as obstacle avoidance (something for which it was not designed). With the introduction of DGPS, the weather RADAR will be used mainly for obstacle avoidance and not for ranging (although it will still be a worthwhile aid providing redundancy in the event of failure of the main nav source). Thus there is little need to improve the RADAR.
There are fewer-and-fewer NDBs and this has to be factored into any re-equipment equation. The ARA is being flown using GPS overlays - probably outside the original design concept.
Experience indicates that (in Northern Europe) few approaches are missed because of the existing minima (simplistically 200ft/0.75nm) even though ARA is used on a fequent basis - mostly in a modified form. Will the introduction of DGPS therefore give operational benefits? That is a complex question because, with the advent of EGNOS and Galileo, it is likely that such equipment will be introduced for a number of reasons - only one of which will be the potential for reduction in the approach minima.
Because of limited secondary RADAR cover in offshore Europe, safety will improve if tracks are flown more accurately. The addition of vertical guidance in the ARA also has the potential to improve safety by reducing the workload on the pilot.
Any equipment review will also take into account other elements that could be provided by satellite technology. As with the GOM, there are gaps in secondary RADAR coverage which, when all helicopters are flying IFR, introduces unacceptable risk of collision. We are likely to see elements of 170's projection which will facilitate a form of collision avoidance, sophisticated communication with operations, flight following etc.
All of this is likely to provide large incremental improvements in safety and is likely to happen with or without the CAA research; it is good therefore that the CAA are providing the background research which will consider the operational requirement and undertake the risk assessment.
The results of the research are being awaited with interest.
Jim
SASless
8th Apr 2006, 15:23
If the CAA is willing to look at GPS approaches to rigs then why not to airports -those plates shown earlier seem to be standalone and not requiring additional navaids.
A very good question I would say.....any answers to the question?
SASless - they are of course.
Jim
zebedee
9th Apr 2006, 20:26
So, the CAA are going to look at this (halle-f#@king-looyah) BUT they have stretched themselves so thin that it won't happen quickly AND do we trust the numpties they employ these days anyway?
In the meantime, boys and girls, please remember that it remains illegal in the UK to use GPS for primary navigation in IMC below MSA (for you NSEA chappies & chappesses, it means you cannot legally do an ARA coupled to NAV - never has been, still isn't.)
Arguments? - please do the research first, then fire away.
Zeb.
PPRuNe Radar
9th Apr 2006, 20:34
Goldenhawk (or anyone who knows the answer), can you tell me where you found the info regarding GPS Approach Trials, please?
UK AIP Supplement S9/2006
Plus you need to visit the Trial website at https://www.gpstrials.leeds.ac.uk/ after the 10th May 2006, for full information before taking part.
JimL, it still seems like all that is needed is a better radar - whether it is used for ranging or obstacle avoidance it needs to be accurate, if it is good enough for one then it must be good enough for the other (there is no point in knowing there is an obstacle out there without knowing exactly where it is). Our minimum let down distance is 1/4 nm on the Sea King and that is with a radar that doesn't even face forwards and is very long in the tooth. I suspect that the use of a weather radar for let downs has never been tested in court regarding legality as to my knowledge there hasn't been a crash resulting from its use.
But since the final element of a rig letdown IMC is going to be pointing at or near to it, will using DGPS let the operators use reduced minimas or must they stay the same because the radar is still the limiting factor?
I take your point re separation between IFR helis - a sort of RVSM if you like.
charron
10th Apr 2006, 00:18
At least radar will tell you what's really out there, like a ship with a helideck on the stern swinging around the bow anchor line. Navigate using the GPS and use the Radar for obstacle avoidance (and maybe range for those ships swinging on anchors). That's kind of how the GOM looks at things.
Where is the approach being flown to 1/4 mile on an uncalibrated radar used for a purpose it was never intended for? That would seem to be very close - most MAP's offshore are 3/4 mile, sometimes down to 1/2 where they get used a lot.
Hard to believe the CAA is taking so long to get on board. If you want to watch a well flown approach, find someone with a GPS that can couple it to an autopilot. I don't understand the GPS vs DGPS issue either. On GPS Approach certification flights the GPS coupled to the autopilot is expected to split the numbers at the end of the runway. If it doesn't, then the installation is faulty. What's that, about 3 meters accuracy? On the last tests I looked at GPS had 95% confidence at 7 meters and DGPS had 95 at 4 meters. What is the CAA arguing about, 1/6th of a rotorwidth?
The luddite attitude towards GPS has certainly managed to keep the avionics of the North Sea fleet firmly locked in the past. All the pilots talk about using GPS because that is what really brings home the bacon, but they have to keep it in hushed tones because the CAA righteously thinks a windshield wiper ADF and "lucille" LORAN (as in " you picked a fine time to leave me") is a far more accurate and reliable navigation source. Even what is installed now would be greated by snorts of derision from any self-respecting American EMS operator. Those lucky enough to operate in jurisdictions that have recognized the benefit of GPS for approach are installing quite different avionics that what is installed in those places that do not have any official sanction, and hence no valid argument for improvement.
charron
SASless
10th Apr 2006, 00:44
Charron,
You should have had the joy of using Decca in a single pilot helicopter on the North Sea! (With no RadAlt either.....but three BarAlts!)
Did anyone ever perform the Decca approach to Sumbrugh at night in cloud, single pilot, and coped with the key and map change?
Talk about something that made Lucille look like Tammy Wynette....sssshhhhh it Doc....two flakes of snow and Decca left quicker than a Rat from an aqueduct.
It's been 30 years since those fun days and I think I can still remember how to operate the Decca due to all the practice one got trying to keep the thing working.
Sasless - now you're talking - Decca was great, as long as you didn't need it in a hurry, or at night , or in bad weather:)
I know someone who decided to compensate for the crosswind on a Decca approach by offsetting one lane to the right:)
Charron - we use 1/4 nm in the RAF Sea Kings as radar let down minima (although the theoretical minimum radar range is 75m) - my point was that a decent radar, ie one designed for more than identifying weather returns, would give reduced minima.
Crab,
The concentration of my last post was on a change that will happen (DGPS with EGNOS); whether industry will fund further development of a device which is primarily used for weather detection and avoidance, I somewhat doubt.
However, en passant you have raised an important issue:But since the final element of a rig letdown IMC is going to be pointing at or near to it, will using DGPS let the operators use reduced minima or must they stay the same because the radar is still the limiting factor?and it is therefore necessary - in the interest of safety - to correct the impression that you may have given (certainly with regard to civilian ARA procedures). As you will see from the text below, all procedures that I am aware of provide a heading offset to ensure that the helicopter is not "pointing at or near to" the target (in JAR-OPS the target miss is set to 300m). The 'offset' is an important part of the procedure; this, and the accuracy issues discussed below, led to the review of the ARA procedure and establishment of the MAPt (at least in the JAA) to 0.75 miles. The stark fact is that, unlike runways procedures, the largest obstacle in the flight path is the target itself.
The elimination/reduction of some of the positioning and tracking inaccuracies and the reduction of pilot workload that will come with the use of DGPS, will be the key to reducing the minima.
Rather than to repeat a previous thread, here is a previous post which explains the issue of RADAR errors and heading offsets:
JAR-OPS (ICAO PansOps based) criteria has an Offset Initiation Point at 1.5 nm - at which point a 10 degree heading change is made which, if continued beyond the MAPt (not permitted by the way), would pass the rig at a mean distance of 300m - 400m. The choice of the MAPt of 0.75 nm was based (very simply) on an aggregation of the position error, RADAR (tracking and ranging) errors, pilot reaction and rate of turn (at the MAPt) to give a probability of collision with the rig at less than or equal to the ICAO Risk Model acceptable target. At the MAPt, the pilot has to fly a rate one turning missed approach of at least 30 degrees into a Missed Approach Arc (identified on RADAR by 5 nm from the target).
An Offshore Standard Approach Procedure (OSAP) based upon the FAA AC 90-80B would have one of two type of approaches: the delta 30 has a 30 degree heading change initiated at the OIP - a distance from the rig of 1.1 nm - the resulting track will take the helicopter to the MAP at a tangent of a circle with a radius of 0.6 nm from the rig; the second method requires the pilot to establish - by 2 nm from the rig - a parallel offset track which passes the rig by 0.5 nm - the MAP is set at 0.7 from the rig.
Each of these methods - JAA and FAA - has its merits but both have defined missed approach procedures established to avoid collision with the rig by a safe margin.
Subjectively, it could be observed that the JAA procedure appears to be optimized for rig acquisition at the MAPt as the rig should be seen on the RADAR, and in the front window, at that point; the OSAP procedure appears to be optimized for missed approach as, at the MAP, it is improbable that the rig will be seen in the front window.
Speaking for the JAA procedure, the MAPt could be closer to the rig if the FAP, OIP and MAPt could be established by a more accurate method than just the RADAR (differential GPS for example). This would remove some of the tracking and ranging errors which now are accounted for.
What was also missed from this original post was the recognition that the CASA ARA system requires a heading offset of 15 degree at the OIP.
Jim
Jim, thanks for the detail, I was aware that there was a heading offset, hence the wording of my post, but not how much.
I come back to the point that if you had a radar with better resolution you wouldn't need such a large safety margin in the procedure as the position of the obstacle (and also therefore the landing area) would be more accurately portrayed in the cockpit. If you trust DGPS sufficiently to reduce the minima because the tracks will be more accurately flown you must trust it to get closer because the position of the obstacle is, theoretically, more accurately known. Personally I would rather rely on real time radar info than a possibly misplotted GPS position.
JimL:
I've found the FAA AC 90-80B document but,
Do you have a link for the JAA document?
Thanks.
Geoffersincornwall
10th Apr 2006, 23:07
See page 1E-7 and subs of JAROPS 3 Section 1, and page 2-E-5 of Section 2
G
:ok:
Aser,
I have PMed you.
Crab,
I'm not sure a RADAR certificated for this type of operations is an option because the of the limited market.
However, you have raised one or two interesting points; unless industry can provide a RADAR that is certificated for these type of operations it is a non-starter; DGPS without obstacle detection and avoidance is also a non-starter.
The revised ARA (or whatever name it takes in the future) will have to meet the hazard analysis required for the introduction of a new procedure. In my view a single piece of equipment will not be able meet the requirement and the combination of DGPS and obstacle-detection-and-avoidance (combined with RADALT) will be required.
The issue of data-base integrity is one which has troubled the industry for some time. Clearly any risk assessed instrument procedure cannot have pilot-entered waypoints; it was this that led to my remark on one of the early posts:One of the continuing issues is the loss of the ability to approach from any direction - once that has to be decided by the software, it will require extensive modification.Unless there is menu selection which can provide a 360 degree approach capability for any location, pilots might be tempted to circumvent the formalism of the system. However, as with RADAR certification, such a software addition will not be provided for a limited market because of the level of software certification that will be required (being a safety related modification).
For all of these reasons, the CAA research is interesting; let's see the result when the research is concluded.
It could be that onshore procedures are a much simpler issue and are concerned mainly with system integrity issues (which will probably be resolved with EGNOS and Galileo). I still consider that 170's suggestion of a combined DGPS and INS provides the best solution for locations without access to other aids.
Jim