GPS Point-in-Space IFR procedures

[reynoldsno1]

I am currently designing a number of ‘point-in-space’ GPS non-precision approaches for IFR helicopter operations. They have the caveat that they are for ‘approved’ operators only, and are intended to allow IFR aircraft to establish visual reference for VFR flight to the destination helipad. The helipads themselves are not equipped/designed for IFR operations

The design criteria allow aircraft to descend to an MDA with a minimum obstacle clearance (MOC) of 75m (250ft). This is the same MOC for an approach to a runway environment with all its associated lights, markings, visual guidance and generally light obstacle density.

I would be interested to hear the views of rotary operators with IFR experience about the philosophy of ‘point-in-pace’ procedures and the minima used. In this case, the procedures are in Class G airspace.

:eek:

[donut king]

250 FOOT MDA seems like a precision approach minimum????

May I respectfully ask who would authorize that minimum to a centre of a downtown core helipad( in among the highrises)?


Second question...... who would want to fly that approach to that minimum?

I can understand those approaches/ minimums to an offshore platform/ runway...... nothing to get in our way. I've done 150 radalt/ half mile vis. with an airborne radar. ( company approved procedures only!!!!!).

Sounds pretty intense!!!!

D.K

[reynoldsno1]

I didn't say the MDA was 250ft - it was to an MDA with a MOC of 250ft i.e. absolute MDH of 250ft (depending on obstacles).

The approaches are not in an urban environment - small provincial towns with an EMS helipad. Ground obstacle density is low, but the topography chages a good deal.

[SASless]

I second the thoughts of the post that questions the wisdom of what you propose to do.....without severe limitations. Offshore approaches with the assistance of airborne radar, ndb's, and the gps can be hairy enough sometimes but to do this overland is asking for a disaster.

Each location should be surveyed and a safe area for the descent could be located, but 250 feet MOC scares the bejesus out of me! This concept joins using areas of VFR as IFR alternates as being frought with peril for helicopters. Due to the lack of fuel range and IFR alternates following a missed approach at the GPS approach site brings a lot of questions to mind. How far from the site will you make the approach....and then transit at very low level in marginal visibility, maybe at night?


If you could assure me of proper weather reporting at the site, terrain and obstacle clearance, traffic control, and fire rescue services, and flight following.....maybe. If the weather is so bad you cannot make a proper Instrument Approach at an airfield then transit VMC.....legally....then what the heck drives you to want to do this?

Please tell me it isn't so your medical crew can save lives of people safely bedded in a medical facility already. Why can the ambulance (assuming it is a scene type incident) not meet you at the IFR airport?

Who is going to ensure that no new towers, masts, portable cranes, oilwells.......advertising balloons get erected in the path of your approach? Will you use the same landing direction or vary it for wind.....any lighted objects on the ground if you are doing this at night? Any kids flying kites in the area.....gosh...I can think of hundreds of problems with this!

And......of course your employer is going to start paying you for this added risk you are taking in addition to the added training, and proficiency you must maintain to do this safely.

Me thinks you are pushing too hard on this one.....GPS is a magic device....and not withstanding the restrictions has more use than we are allowed to utilize...but this concept needs to be given a real "Murder Session" before you implement it.

[syd_rapac]

Reynolds,
not working in Oz are you??????

SASless.

IFR GPS approaches have been in use in OZ for a number of years specifically at locations not serviced by an aerodrome with a ground based nav aid or the terrain limits getting in there in bad WX.. They are significantly safer than attempting to scud run into a one way valley as MAY have occurred in the past.

There are a number of constraints which call up a range of requriements for man, machine and alternates. These include --TSO'd equipment - mandatory alternate with ground based aid eg NDB, omni or ILS. And yes to date the approaches together with the buffers are specifically test flown to check for uncharted obstacles. Great stuff if you ever get the chance to do the inspection flying.

Limited distribution ensures someone doesn't try and fly it in a Supercub or Maule.

Also from one perspective some flights can be regarded as rescues from the clutches of the hospital. Not all hospitals are equal.

If you want some better contacts in both the procedures designers and regulators we can assist. For info there was a proposal going to ICAO earlier in the year for amendment to the ICAO design standards to permitt these operations. Sorry can't remember the part off hand.

Cheers

Syd

[rotorque]

Hi,

Syd_rapac I agree with your sentiments totally. It intrigues me how many pilots will read what you can't do instead of what you can do. Of course I say that with the obvious tongue in cheek it deserves, but the point still needs to be made.

My opinion of IFR flying is simple, "this is what I am trained to do, so I will go out and do it". I trust the people who survey the sites, and I follow the rules that have been written. It is rare that pilots become unstuck when they follow the proceedures layed out.

The questions raised above may be directed to a more general type of pilot who is not as current as the dedicated pilots (the only pilots) who will be using the proceedure.

As to minima's etc, here is an example of the numbers we deal with in IFR operations. In Australia, on the missed approach the surveyed clearance from obstacles is 100 feet. Dosn't that sound a lot less than 250 feet. Of course it does, but that dosen't make it unsafe.

Cheers

[reynoldsno1]

Thanks for your input guys – sorry for the delay in replying. We seem to have some polarised views with the division apparently between the Northern & Southern Hemispheres. Perhaps I should put things in a proper context…

The procedures are to be used in New Zealand, and they are not the first. We now have a lot of GPS operating and design experience in the country, and overseas - including places like Nepal where the terrain is even more unforgiving than Godzone…

The operating environment in NZ is quite different to UK/Europe. Hospitals are few & far between, and in the less populated the medical facilities are less than comprehensive. The majority of provincial airports are also pretty basic.

New Zealand is very well surveyed, but we recognise the possibility of uncharted obstacles and a contingency is included during the design process. This equally applies to any airport approach here, and we often get reports of kite fishermen (never mind kids…) near the coastal airports – they can have quite a few km of line hanging from their (really quite large) kites.

What we want to avoid is the scenario of carrying out an approach at an airfield and then have the aircraft wandering around for miles trying to get to a destination in marginal conditions – a touch of the old helicopter IFR (I Follow Roads) principle. Surely it’s better to give them a properly designed approach using ICAO criteria that will put them in a position to transit VFR over a much shorter distance.

The procedures are for the use of specific operators only. The approaches themselves are checked using a portable GPS Flight Inspection System, with the operators themselves providing & flying the aircraft. The whole design & approval process is very formal – these are not sketches on the back of a fag packet.

Internal discussions here are really concentrated on using the NPA MOC of 75m. Since ICAO do not specify circling minima for helicopters there has been a thought to use the Cat A circling MOC of 90m, but then again what will this actually achieve? The IFR operating procedures for using GPS are well defined and relatively mature in NZ now, so that is not really an issue, and the operators are comfortable.

I appreciate your comments – it is always worthwhile getting truly unbiased and objective viewpoints!

[S76Heavy]

How about using FLIR or NVGs so you can actually SEE where you're going? I find offshore Radar approaches (using GPS waypoints as back up) difficult enough, and then I know that the rig is the only obstacle to worry about, anything else worth avoiding shows up on radar and I've got my go around pre-planned.

I would be a bit concerned about flying the GPS letdown to very low minima and then suffer some sort of system failure to distract me momentarily.

I suppose these comments prove to the rest of you that I fly in the Northern hemisphere..:D

[GLSNightPilot]

We've been doing these approaches to our onshore bases for a few years now, down here in TX/LA. Our MDA is 300', .5SM vis. All the obstacles in the area are on the approach plate, along with the distance/heading to each heliport from the MAP. It really isn't that bad, since we fly VFR at 300/1. It does require some concentration, but no more than an offshore approach. It really helps to know the area, especially the towers, etc that stick up all around.

[syd_rapac]

Reynolds,

You need to talk to Martin Chalk and Dolf Fickler in Air Services in Canberra. They have done all the Australian design. Bob Kennedy in CASA Oz did the presentation to ICAO , I think.

Syd

[helmet fire]

Reynolds,

Having also done these procedures, I cannot agree with SASless here, rather I have to agree with Syd. It is an important distinction that ALL of these approaches require alternates of ground based systems. 250 ft sounds reasonable given that the MOC is based on a large tolerance area that is determined by ICAO standards. You might be intrested to know that HEMS operators drove the GPS/NPA introduction into Oz. The first approach used WAS a point in space approach to Westmead Hospital!!

Australia has recently been to the ICAO conference on GPS approaches which helped to set a standard for the issues you raise. Because the approaches had been in operation in Oz for several years, and the criteria had been already established and incorporated into Oz docs, the Australian delegation was able to provide the ICAO commitee with a eady made solution to the standardisation issues. The list of names Syd provides above are excellent sources for info on this, and they were/are instrumental (no pun) in moving this issue forward. Also try Peter Heath (Ops manager) and Terry Summers (pilot) at CareFlight in Sydney.

I believe it is essential that such approaches are established to maximise the versatility of the helicopter and to provide the best possible HEMS service. Good luck doing so.

Edited to korekt spelling!:D

[reynoldsno1]

Thanks guys/gals. I do know both Dolf Fickler & Martin Chalk. The procedures are all designed to ICAO guidelines, and are probably very similar to those in Oz. I am essentially reviewing the basic operating philosophy underlying these types of approach, and wanted to hear others' views as it is easy to become blinkered without some external input. This is all very useful...

[Nick Lappos]

I'm concerned that anyone really thinks that ground based is better than space based. Give me a break!

The system that can find your Fedex, guide a cruise missile through a window (in the wrong embassy, perhaps) and also drive the map in your Toyota is certainly better than any ground based system.

I am Co-Chair of the FAA Terminal Area Operations Advisory committee, and we are launching non-precision and precision space based approaches, with mins down to about 100 feet, eventually to a hover.

With GPS, GLONASS and Galileo, the sky is the limit. I have personally flown about 250 precision approaches to a hover in a modified S-76 with a DGPS corection transmitter as the only ground based aid, and that is now removable with WAAS.

For the best knowledge about point in space procedures, please email me, as I have contacts who write these procedures and are empowered to provide for FAA approval, and they could give you expert guidence. They are commercial, so I must respect pprune's policies.

[syd_rapac]

Nick,

I think you may have mis interpreted the ground based aid comment.

Whilst we wholeheartedly agree with space based unfortunately the RAIM system in Oz does drop out, and it can and has occurred halfway down the approach.

As you state all the approaches you flew have dgps correction where the current stuff in OZ does not use any ground based supplementation. It is reliant solely on the TSO'd receiver.

The carriage of an alternate with a ground based aid is a safety backup due to lack of GPS system reliability.

As I previously stated the procedures stand alone and are being used typically to hospitals well outside ground based aids coverage.

I would be interested in a URL to any design rules that do not require WAAS or supplementary DGPS.


Cheers

Syd

[Nick Lappos]

Syd,

Thanks for the clarification. The sat drops are a problem as we get away from the equator, for GPS, but no issue for Galileo or Glonass.

Until a "Universal" satnav (receiving all three at once) is approved, is it possible to substitute another airborne sensor, such as Loran C or Inertial as the backup? If a Nav quality Inertial were used, and it simply re-synched to the GPS until the RAIM declared GPS kaput, it would add only a few feet to the position error at the bottom of the approach (at 0.7 NM/Hr drift rate, that's only 1000 meters per hour. In one minute, the Nav solution would degrade by only 1000/60=17 meters).

The cost is high, but it weighs against the economics of the assured approach.

Nick