ILS Categories. Do I have the right idea?

[mad_jock]

Certified in 1992 and was the first JAR25 and FAR25 certified turboprop which I think there is a BRNAV requirement with.

Its also certified for CAT II.

[peterh337]

Certified in 1992 means designed several years before that, which is just about pre-GPS.

With INS with DME/DME corrections, GPS was never a priority. Only the most modern airliners have GPS integrated into the INS, and AFAIK they have three of them.

You are living in another age

There are numerous ways to end up with crap GPS reception. VHF interference (11th and 13th sub-harmonic of 1575MHz) is a common one (try transmitting for 20-30 secs on 121.2 and see what happens to the GPS satellite signal levels). ELT pi-tank resonance (triggered by VHF transmission anywhere around 121.xx to 122.xx) is another. Crap installations are another

So if the RVR is greater than 550m, a crew could fly a CAT I, II, IIIA or IIIB approach

I think there is a "story" behind this, too. In UK airspace, a single pilot is limited to 800m for takeoff and landing. With high intensity runway lighting and with an autopilot which can fly the ILS all the way down to the published minima (say 200ft DH) this improves to 550m which is the normal published vis figure on Jepp plates.

That's AIUI, anyway.

Incidentally, I am told the standard answer on an IR test is supposed to be 800m and if you answer with 550m then you fail, because you are not supposed to use the AP.

[mad_jock]

Nope was 90's when it was designed and they all came fitted with GPS of some form even if it was a trimble.

The age I am living in is the age which 95% of the world fleet of aircraft are in.

How many aircraft types have been certifed since 1992? Not many.

Maybe a Q400 driver can tell us what thier box of tricks uses I suspect its DME/DME though.

I know you will never be swayed with your reliance on GPS and the rest of us are dinasours. For me it is a very useful tool in the box which gets treated like any other bit of information in the cockpit. ie it gets cross referenced against something else.

Personally I am quite glad that there are cooler heads out there putting the brakes on ditching all the rest of the gear and putting all our eggs in the one box.

Personally I do think we will get them but it won't be with the current kit.

[Midland Transport]

Just to add 1 more complication. For single pilot operations in the UK the RVR minima is 800m however if you have a coupled AP then the RVR brecomes 550 (or the stated RVR) as was previously stated. However, for the DH if your A/P is approved to 200 ft you should then apply 1.25 times that ie 250 DH. So the resulting combination would be DH 250ft RVR 550M if you used a coupled A/P. A further complication is that some autopilots do not have a state minimum operating height.

[peterh337]

gets cross referenced against something else.

I never said it doesn't.

The anti GPS crowd always takes the same tack:

using GPS = sole reliance on GPS

which is bollocks.

For single pilot operations in the UK the RVR minima is 800m however if you have a coupled AP then the RVR brecomes 550 (or the stated RVR) as was previously stated. However, for the DH if your A/P is approved to 200 ft you should then apply 1.25 times that ie 250 DH. So the resulting combination would be DH 250ft RVR 550M if you used a coupled A/P. A further complication is that some autopilots do not have a state minimum operating height.

Interesting; thanks

On the UK CAA IRT one is supposed to add 50ft anyway to the altimeter reading for the DH (I am told) so 200ft is never actually achievable.

Is any of this changing under EASA OPS?

[S-Works]

Blimey all these luxuries. I am lucky to have hot air bleed to warm my feet....

Although we are GPS BRNAV!!

[mad_jock]

I am not anti GPS.

And for certain situations ie above MSA the risk is low enough that its acceptable.

But below that there are so many external factors which effect the quality of of the position that the risk is unacceptable currently especially as there are no warnings when it does go out.

I suppose you could have a tone on a fequency which triggered when the local GPS strayed away outside tolerance from a fixed reference. Which would then flag in the cockpit.

bose the art of landing an aircraft when you can't feel anything from your knee down.

[mm_flynn]

Originally Posted by mad_jock

I am not anti GPS.

And for certain situations ie above MSA the risk is low enough that its acceptable.

But below that there are so many external factors which effect the quality of of the position that the risk is unacceptable currently especially as there are no warnings when it does go out.

I suppose you could have a tone on a fequency which triggered when the local GPS strayed away outside tolerance from a fixed reference. Which would then flag in the cockpit.

bose the art of landing an aircraft when you can't feel anything from your knee down.

Assuming your GPS is approach approved you probably should get the owner/operator to have it checked out.

You should have RAIM integrity warnings that does give you your desired flag if the GPS position becomes unreliable. Also, it should be exceptionally rare for an approved installation to loose signal coverage - there must be something wrong with your installation or you are operating in known jamming areas.

Finally, GPS in and of itself is approved (even for Europe) at its basic level as the sole means of navigation to well below MSA. If you have WAAS then it is approved for approaches to ILS like minimums. (obviously it is always good to use the maximum amount of information to crosscheck any piece of magic - new or traditional)

In the US it is even approved for RNP approaches that no other navigation system provides the necessary accuracy and integrity to execute.

[peterh337]

especially as there are no warnings when it does go out.

Say again?



What century are you in, MJ?

[mad_jock]

Yes the known jamming area is called the United Kingdom which they are allowed to jam at any time without NOTAM. There are airborne jammers as well for the war games. Around any of the Mil ranges though out the UK they can and do Jam. Recently they had it brought up in Parliment to get them to stop jamming during a war game because all the fishing boats were getting lost and with the current restrictions it meant that they were looking at not finding there fishing spots on the few days a month they could actually fish.

This isn't just one aircraft its happened in getting on for 36 airframes in my log book. And they are all public transport CofA's.

They will be approached approved but as there are very few GPS approaches in europe I haven't done one in anger. I did submit a form or two for the test ones in the UK but unfortuantely it didn't aid the cause because RAIM dropped and we converted to a visual without getting to the FAF but that could have been the FRA Hawker that was operating in the area for an exercise.

The only warning that comes up on the units is a very small flashing msg light and when you go press it twice it comes up RAIM fail, check your position or something like that. Most folk ignore it because it goes on and off at various points and usually goes away after a few mins.

But I have every expectation that all my experences will be put down to crap aircraft, crap equipment, crap pilots(even though we don't need a GPS to get where we are going). That its no fault of the GPS system and I should get out of the dark ages and put my faith in it when scraping my arse to the deck in 600m and OVC 001.

Peter we have no warnings whats so ever on the primary instruments when it fails.

[englishal]

But below that there are so many external factors which effect the quality of of the position that the risk is unacceptable currently especially as there are no warnings when it does go out.

I think you'll find that GPS is probably the best nav system with regards to warning the pilot when there is no GPS signal!...you get flags, messages, etc...Is yours a certified installation or is it a hand held mounted on the windscreen?

Actually the GPS jamming trials didn't even affect my 430W or Aera, even though I flew slap bang through the area. Mind you I have it properly mounted and IFR certified.

[achimha]

I think you'll find that GPS is probably the best nav system with regards to warning the pilot when there is no GPS signal!...you get flags, messages, etc...Is yours a certified installation or is it a hand held mounted on the windscreen?

I've had spurious issues with a GNS430W ranging from signal degradation to complete loss of signal for some time without a clear pattern. It was eventually traced down to a defective unit. Note that in my IFR certified installation, the loss of signal did not make the CDI show an off flag!

The user interface of the GNS430W is absolutely terrible and its habit to constantly pop up stupid and irrelevant messages that you only see when you press a button trains pilots to not assign any importance to them.

I got my license when GPS was already ubiquitous and always considered the whole VOR/DME stuff to be rather annoying but after my experience with the GNS430W, I see myself tuning VOR/DME stations enroute and perform cross check.

[peterh337]

I see myself tuning VOR/DME stations enroute and perform cross check.

That is only sensible.

Re the CDI flag, that's interesting, and probably intended behaviour. I originally had a KI-525 HSI whose NAV source could be switched (as is traditional) between GPS (from the GPS) or NAV (VOR/LOC according to the frequency selected on the radio). The Invalid flag was never driven by the GPS, AFAIR. Now I have an EHSI (Sandel 3500) and that makes it very obvious if the GPS is not picking up a signal.

Re GPS failures, I've had them too. One off Italy in 2004, halfway between Brindisi and Dubrovnik, at about 1000ft. Lasted a few minutes, and affected all three units. That one was porb99 jamming. One departing from Padova (Italy) in 2006 which lasted from startup for about 30-45 mins, which affected only the one GPS (KLN94) and that one was probably a corrupted constellation table in the GPS, which always takes a while to clean up. I then had a strange Garmin 496 failure in 2010 when a specific DME frequency was selected, without any other GPS being affected, which is not explained by any subharmonic of 1575MHz.

Out of a total flying time of about 1400hrs that is under 0.1% i.e. a 99.9% + availability. And if you predicate GPS approaches on obvious GPS availability, let alone RAIM, you are looking at a 100% reliability. I've never had a GPS malfunction which wasn't totally obvious on the GPS.

In flight, the possible lack of a CDI flag should not bother the pilot because few would (or should) be flying with GPS using a CDI. That is probably how the "old school" started using GPS, and indeed the original non moving map units (Trimble etc) did only that i.e. generating a cross track error which would be viewed on a CDI. Today, nobody should be flying with a GPS in that way. There is only one thing worse and that is plotting the GPS coordinates on a map One should be monitoring the GPS moving map as the very primary source of navigation data. That map is the "big picture". And if you lose signal, that is where any error messages will appear.

Admittedly a Garmin 430 has a map too small to be of much use, which is why I don't have a Garmin 430 And if I did, I would have it feeding a nice size MFD. I don't consider a single GNS430 sized unit as adequate for IFR.

[BackPacker]

How do you fly a GPS approach then? I have no IR but I would assume that you would use the CDI/GS (slaved to the GPS) as primary guidance.

If a GPS failure would not throw a flag right there in your face, you might miss it altogether.

[silverknapper]

Adding to DA

Peter

It was a while ago but for my IRT we added 50' to the MDA but not to the DA. A practice which is common now in the name of stabilised approaches, non precision. It becomes a 'virtual' DA where one can initiate a GA at this new DA and with any inertia still not bust the MDA.

[peterh337]

How do you fly a GPS approach then? I have no IR but I would assume that you would use the CDI/GS (slaved to the GPS) as primary guidance.

That is true...

I would guess that if you are driving a dumb CDI from a GPS, the CDI flag has to be connected appropriately.

That is an issue in the avionics business; some installers just throw in a GNS430, connecting up the basic wires and that's it.

Normally, of course, you use the autopilot and monitor the approach on the moving map, on which the entire approach is depicted

One would not just watch the CDI and not the GPS because, for example, one needs to be sure the GPS is correctly sequencing to/through the approach, with the sensitivity dropping from 5.0nm enroute to 1.0nm by the IAF, to 0.3nm at/past the FAF. This stuff is only on the GPS screen.

It was a while ago but for my IRT we added 50' to the MDA but not to the DA. A practice which is common now in the name of stabilised approaches, non precision. It becomes a 'virtual' DA where one can initiate a GA at this new DA and with any inertia still not bust the MDA.

Interesting... I was told differently: add 50ft to the published ILS DA, but add nothing to the published NP MDA. With the ILS you go missed at the newly calculated DA and climb straight up. With the NPA you fly level from the point where MDA is reached (at an altitude which is between the published MDA and that plus 50ft) all the way to the MAP and then climb. If you bust either figure you fail, and if on the NPA you climb outside that 50ft band (before the MAP) you also fail. I will need to revisit this when I get the plane out of the Annual...

[silverknapper]

At the risk of teaching granny to suck eggs:

There are two ways taught to deal with an MDA.

1. Fly level at MDA until the MAP. You are correct, the examining limit for this method is -0/+50'.
2. My previously mentioned add50' to MDA and treat as a DA. Though this 50' would increase with aircraft weight. Basically you need a margin which would allow you to initiate the GA and not bust your MDA. So you fly a stabilised descent to the Virtual DA then go around. This may be before the MAP, depending on how well you have judged your descent path.

The second method inevitably could lead to you missing out on the last 50' of cloud base, but is much safer than levelling off fully configured. Indeed for commercial operators EU ops made it mandatory.

Of course the basics still apply. MDA is absolutely not to be busted. DA is where the GA must be initiated so in a large enough aircraft this could be busted whilst engines spooled etc. this is ok.

[Denti]

How do you fly a GPS approach then?

My aircraft is certified to fly them with both GPS INOP. As long as the RNP is higher or equal to 0.3.

However, GPS approaches are a thing of the past, nowadays it is RNAV or RNP approaches. Same here, down to RNP 0.3 i do not need GPS, helps to have it though of course.

[peterh337]

Is that a joke?

[mm_flynn]

Denti is just having a US pedent wheez. All that is required for a US 'GPS' approach is an approved RNP 0.3 navigation system. It doesn't actually have to be GPS. But for the private flyer I don't believe there is any other option (and I am not sure about any options other than GPS no matter what civil aircraft one flys).