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Use of GPS in lieu of DME/ADF

PostPosted:Tue Nov 04, 2014 7:47 pm
by Cookie
I see that G-BLEW mentioned something about it in this month's FLYER.

Use of GPS in lieu of DME/ADF
Whilst RNAV5 has removed the need for en-route NDBs (and VORs), the use of GPS in lieu of DME and ADF should be permitted in the intermediate approach, holding, and missed approach. This would remove the current issue which appears as the excuse for including NDBs in the design of RNAV approaches, and therefore requires operators aircraft to have an ADF installed to use a GPS approach(!). GPS in lieu of ADF and DME should also be permitted on all localiser-type approaches and VOR/DME approaches.

After all, pilots in the US have proven it on our behalf for over fifteen years!

http://www.aopa.org/Advocacy/Air-Traffi ... of-DME-ADF

There are a few sensible caveats, which the FAA mandate, included in the above link.

Cookie

Re: Use of GPS in lieu of DME/ADF

PostPosted:Tue Nov 04, 2014 7:57 pm
by Bathman
Yep. Definitely. I think this would have a very positive impact.

Re: Use of GPS in lieu of DME/ADF

PostPosted:Tue Nov 04, 2014 11:02 pm
by riverrock
We need a lot more GPS approaches before we would get the benefit. However I do agree.
Is there a definitive answer anywhere on whether GPS counts as DME in UK / EASA land? Definitivly saying this would also be of huge benefit.

With LAA aircraft in the process of being signed off for IFR, there are going to be a lot of people thinking about what Nav equipment to install to get the use out of it. I don't see many wanting to install ADFs and many power systems I suspect wont support DMEs.

We're thinking about installing a 430W in our permit but this will, in reality, mean we are relying on SRAs / Vectors to ILS as the approaches at Prestwick don't have GPS equivilients so rely on DME / NDB for parts of them. Allowing us to do curent approaches using GPS would have great benefit.

PostPosted:Wed Nov 05, 2014 3:18 pm
by Peter Gristwood
With LAA aircraft in the process of being signed off for IFR


With SOME permit aircraft in the process of being signed off for IFR !!!!! :twisted:

Re: Use of GPS in lieu of DME/ADF

PostPosted:Wed Nov 05, 2014 3:36 pm
by riverrock
Indeed - but then - only some CofA aircraft are signed off for IFR too (I know the Robin at our club is Day VFR only).
I suspect there will be an announcement soon on the PtoF front :)

PostPosted:Wed Nov 05, 2014 6:40 pm
by GrahamB
riverrock wrote:We're thinking about installing a 430W in our permit but this will, in reality, mean we are relying on SRAs / Vectors to ILS as the approaches at Prestwick don't have GPS equivilients so rely on DME / NDB for parts of them.

Read carefully what Cookie wrote. A DME would still be required for the Final Approach segment, so getting a GNS430W alone would not help you there.

PostPosted:Wed Nov 05, 2014 7:30 pm
by Cookie
GrahamB wrote:A DME would still be required for the Final Approach segment, so getting a GNS430W alone would not help you there.


Quoting myself :? :

GPS in lieu of ADF and DME should also be permitted on all localiser-type approaches and VOR/DME approaches.


Cookie

PostPosted:Wed Nov 05, 2014 8:15 pm
by GrahamB
Cookie wrote:
GrahamB wrote:A DME would still be required for the Final Approach segment, so getting a GNS430W alone would not help you there.


Quoting myself :? :

GPS in lieu of ADF and DME should also be permitted on all localiser-type approaches and VOR/DME approaches.


Cookie


In that case, with respect, I don't think you've worded your request very carefully, as it is not clear at all that you mean for all segments in the second paragraph. :)

PostPosted:Wed Nov 05, 2014 11:46 pm
by Paul_Sengupta
I understood it... ;-)

PostPosted:Thu Nov 06, 2014 1:38 pm
by bookworm
I feel the need to quote the RTC Panel Interim report...

The CAA’s response to the GA Red Tape Challenge explicitly discusses innovation in GA, for example:
“The CAA’s GA Programme is intended to help foster innovation in the GA sector by considering the potential. Initiatives already started include:
• creating a ‘commercial experimental’ aircraft category to facilitate proof-of- concept flight testing subject to professional competence and proportionate operational restrictions;
• simplifying processes for modification, changes and repairs;
• improving the substitution of obsolete or out of production materials;
• allowing certain Permit to Fly aircraft to fly at night and/or in instrument conditions if appropriately equipped; and
• simplification of the means to allow flights for test purposes (without a standard valid Certificate of Airworthiness/Permit to Fly)."

Specific innovation initiatives are discussed below, and we focus first on the general principles of managing risk associated with innovation in a regulated domain such as aviation. Many of the risk- management aspects described in the previous sections come into play. Adoption of new technology in aviation tends to follow a path of caution, for good reason. The stakes are high if an inadequately tested piece of equipment fails in service. Nevertheless, as in all aspects of safety management, there are trade-offs between the safety value of new technology and the associated risk; only by doing something differently will safety be improved. A case study is instructive.

The CAA’s reluctance to adopt Global Navigation Satellite System (GNSS) technology has probably been the area that has most threatened the credibility of the CAA as a safety regulator with the GA community. The Global Positioning System (GPS) has been available as a navigation tool since the late 1980s. GPS receivers suitable for air navigation started to appear on the market in the early 1990s, and GA pilots rapidly realised their potential for improvement of situational awareness and reduction of cockpit workload.

On 17 February 1994 the US FAA introduced Phase 2 of its GPS Approach Overlay Program. This allowed pilots to use a TSO C-129 A1 GPS receiver to fly an overlay of an approach designed for conventional navaids. On 28 April 1994 Phase 3 allowed these approaches to be flown without any conventional navaids or on-board receiver avionics. Substitution of GPS fixes for NDB or DME based navigation was also authorised. As a consequence, most owners of US aircraft, including GA aircraft, disposed of ageing and unreliable conventional navigation equipment, in particular ADFs, and invested in modern GPS equipment.

By contrast, in the UK, regulatory acceptance of GPS has proceeded at a ‘snail’s pace’. Many UK GA pilots have used handheld GPS receivers as their effective means of navigation for VFR and IFR since the mid-1990s, in the face of warnings that it must not be used as a primary means of navigation. Even GPS receivers that are, in effect, required to meet airspace requirements for Performance Based Navigation still may carry a placard prohibiting their use as a sole or primary means of navigation.

In 2006, the UK CAA announced a trial of GPS approaches for General Aviation aircraft at six UK airports. Even after successful trials, it took several years before airports were authorised to use even these approaches because of difficulties establishing safety cases. There has never been an overlay program in effect. In December 2011, the UK CAA published AIC Y 107/2011 finally exempting aircraft from the requirement to carry an ADF as a prerequisite merely for flying IFR in controlled airspace.

It notes however:

“4.2 Precision or Non-Precision Approaches with Missed Approach based upon NDB
The missed approach based upon an NDB is an integral part of the approach procedure and therefore an aircraft must be equipped with ADF to conduct the missed approach procedure.“

Of the few GPS approaches now available in the UK, most, such as those at Gloucester, Blackpool and Cambridge use an NDB as part of the missed approach procedure. Aircraft flying the procedure must therefore be equipped with an ADF, even though for all practical purposes the equipment is likely to remain switched off while the missed approach is flown, with great precision, using GPS.

There is an unquantified hypothetical risk (perhaps better termed a “hazard” in standard safety terminology) associated with the substitution of GPS fixes for NDBs: the obstacle clearance criteria are, technically, different. However, the practical risk associated with such a substitution is, as proven, by experience in the USA, negligible. Yet in deference to this hypothetical risk, the benefits of the new technology are largely lost.

It not credible that the requirement for an ADF should be the result of an objective analysis of the balance between the risk associated with GPS fix substitution and the cost of continuing to carry ADF equipment in a serviceable state. That this remains the legal situation in the UK two decades after the FAA put its GPS Approach Overlay Program into effect (with no net safety issues) is a sad indictment of the appetite of the UK CAA to embrace innovation.

PostPosted:Sat Nov 08, 2014 8:13 pm
by chrisbl
The US adoption of GPS way ahead of anyone else is down to two main factors

1) The GPS system was own by the US and on the basis that it was funded by the taxpayer then taxpayers should benefit. Not something our governments tend to believe in.

2) The GPS equipment companies are mainly US companies and the adoption of GPS gives the US industry a massive home based and making the likes of Garmin, Honeywell etc dominant across the world.

Its a case as much of US commercial interests being looked after as much as the desire to introduce a new technology. Never underestimate the power of money in the US.

PostPosted:Sun Nov 09, 2014 8:19 am
by Bathman
But that hardly makes the CAA stance palatable does in. Huge evidence base yet totally ignored.

PostPosted:Tue Nov 11, 2014 6:46 am
by chrisbl
Initially yes. The GPS constellation was under the control of the US military and they did degrade the gps signals to suit US interests.

No problem mucking things us for US citizens, but non US governments would be unwise to put their eggs into a basket they had no control over.

Hence why ground based systems were continued with.

Since the expansion of the GPS satellites, with the European system as well, the arguments for holding back have reduced.

The priority though should be the expansion of GNSS based navigation for CAT. GA in the UK is not really the priority.

The current trials of RNAV departures out of Heathrow are proving interesting (apart from brassing off a load of people in Ascot) but that is where the priority should be- greater good etc.

PostPosted:Mon Nov 17, 2014 8:20 pm
by User72
CAA GA Unit will be looking into permitting the use of GPS in lieu of ADF & DME in the New Year - so said Tony Rapson today.
In my view claiming GPS in inaccurate is as daft as claiming ADF is accurate. If you fly the approach according to the plate who would ever know that you're using GPS instead of ADF or DME? Just get on with it...

PostPosted:Mon Nov 17, 2014 8:49 pm
by Paul_Sengupta
I don't think anyone's saying that GPS is inaccurate, it's more that it's easy to interfere with or jam and if that happens you have no way of flying an accurate missed approach.