IFR in kitplanes

[IO540]

The Garmin 496 GPS-derived altitude is a helluva lot more accurate than an altimeter, especially with EGNOS.

Especially if you don't quite know the QNH for the place you are going to

[hoodie]

Originally Posted by Genghis

(or in a permit aircraft, over built up areas...)

That one's no longer relevant - the permit restriction for flying over BUA was rescinded in 2008 (for sub-1500kg aircraft - and strictly it is an "exemption from a prohibition").

Here's the LAA paper (by John Brady) that successfully proposed its removal.

Otherwise: Interesting thread, this.

[Genghis the Engineer]

Originally Posted by IO540

The Garmin 496 GPS-derived altitude is a helluva lot more accurate than an altimeter, especially with EGNOS.

Especially if you don't quite know the QNH for the place you are going to

Garmin's GPS will give you geopotential altitude, which is best for terrain avoidance, although non-conservative. RPS is more conservative.

It will not give you pressure altitude, which you need for quadrantial/semicircular rule, it will not give you separation from controlled airspace, and it will not have you using the same reference as anything else out there that may fly into you.


Incidentally you said earlier that I didn't mean IMC capability on some VFR flights wihout a clear horizon, I actually meant radio navigation capability. Nope, I meant what I said - loss of attitude information will kill me quite quickly, loss of positional awareness VFR will take until I run out of fuel and whilst it's a very good thing to know where I am, it's a much better thing to know which way is up.

G

[Genghis the Engineer]

Originally Posted by hoodie

That one's no longer relevant - the permit restriction for flying over BUA was rescinded in 2008 (for sub-1500kg aircraft - and strictly it is an "exemption from a prohibition").

Here's the LAA paper (by John Brady) that successfully proposed its removal.

Otherwise: Interesting thread, this.

Actually, it's http://www.caa.co.uk/docs/33/ORS4_807.pdf.

But thanks for reminding us of that.

(Nonetheless, I'll personally continue to avoid overflying built up areas in any single engined aeroplane myself).

G

[hoodie]

Genghis, I was correcting you - not reminding you.

Villages and small towns don't bother me; obviously overflight isn't the issue - 'glide clear' is.

[IO540]

RPS is more conservative.

Sure, in the sense of fairly uselessly adding 1000ft to everything, on some days

It will not give you pressure altitude, which you need for quadrantial/semicircular rule, it will not give you separation from controlled airspace,

If a GPS delivers true altitude, then it's good for CAS separation where CAS is defined as altitude.

Obviously I agree re the other reasons for barometric altimetry... I was just being provocative

I posted this a while ago. That is an old GPS, without EGNOS. For some reason I didn't include the yoke-mounted Garmin 496 which uses EGNOS and is super accurate in altitude.

[Rod1]

“You can always fly IFR in VMC in anything, quite legally”

Absolutely not allowed, if you do this overtly you will get reported as you are in breach of your permit to fly which states daytime VFR only, flying under IFR is not allowed on a permit!

Rod1

[Genghis the Engineer]

Originally Posted by Rod1

“You can always fly IFR in VMC in anything, quite legally”

Absolutely not allowed, if you do this overtly you will get reported as you are in breach of your permit to fly which states daytime VFR only, flying under IFR is not allowed on a permit!

Rod1

Which is a silly bit of wording, since you can be IFR and VFR simultaneously in VMC. It, of-course, means, stay VFR.

Originally Posted by IO540

If a GPS delivers true altitude, then it's good for CAS separation where CAS is defined as altitude.

Obviously I agree re the other reasons for barometric altimetry... I was just being provocative

And wrong. If CAS is defined by altitude, it's defined by pressure altitude on the appropriate QNH, not by geopotential altitude. If it's not defined by that, it's on flight level, which is still pressure altitude, but on 1013.25hPa.

G

[europaflyer]

<quote>
Which is a silly bit of wording, since you can be IFR and VFR simultaneously in VMC. It, of-course, means, stay VFR.
</quote>

Don't think so. You can be either under IFR or VFR in VMC, not both by definition, just as you can be either IFR of VFR in IMC - although obviously the VFR option is to be avioded

So, we seem to have concluded that flying under IFR or in IMC in kitplanes is a no-go. A shame, as as people have pointed out the panel fits in some kitplanes is far better and safer than most of the rusty scrapheaps in Group A which are lucky enough to have a mound of happy rubber-stamped paperwork attached - which, of course, doesn't and never has made the ground any softer...

I agree with previous posts that getting the CAA to change its mind is impossible - we've enough on trying to fight off the Europeans which none of us voted for, wanted or need, and exist solely to perpetuate their own beaurocracy.

/rant mode off/

[IO540]

If CAS is defined by altitude, it's defined by pressure altitude on the appropriate QNH

I wonder where this is stated.

If CAS is defined by altitude, it is defined by altitude, which is defined as the height above sea level.

Is there anything in e.g. the ANO which says that the only acceptable means of determining altitude is using barometric altimetry?

It would imply that non-radio flight OCAS is illegal, because the only way to obtain the QNH is using a radio. And the RPS is no good for CAS avoidance; in fact it could easily result in a bust.

It would also make all modern GPWS systems illegal because they use GPS derived altitude, and they compute whether the trajectory conflicts with anything in their internal terrain database. Using GPS altitude enables the system to function even if the pilot has set the wrong QNH somewhere.

So, we seem to have concluded that flying under IFR or in IMC in kitplanes is a no-go. A shame, as as people have pointed out the panel fits in some kitplanes is far better and safer than most of the rusty scrapheaps in Group A which are lucky enough to have a mound of happy rubber-stamped paperwork attached

I agree, but IFR is a bit like no longer being a virgin; it is all or nothing. And many "homebuilt/sports" types (I use the term loosely) are self evidently flimsy. I am going to draw the usual flak here from the usual people but there are loads of in-flight structural failures in these categories, and this puts a question mark on flying in IMC, where there is often a great deal of turbulence. And IFR in VMC is a very peculiar UK-only concept which is almost without any utility value.

Sure some homebuilt types are very strong, etc, but who is going to look at a structure and say this one is OK but this one is not OK. For many types, detailed design data either doesn't exist or (as with that type recently grounded by the FAA; can't remember its name - was it Czech?) the test flight data (particularly Vne+ tests to check for flutter) may have been, shall we say, obtained using less than comprehensive means. I am Czech myself

So I think nobody wants to get very involved in allowing blanket IFR in non-CofA types. At best, it would have to be limited to OCAS, which would eliminate a lot of the utility value, and if it was not thus limited, you could do full Eurocontrol IFR flights in a 450kg machine which can do say 80kt, say 30kt GS in a decent headwind, and getting agreement for this from all interested parties might be tricky.

Maybe those who have been saying that IFR for homebuilts is just around the corner know something I don't know (highly likely) but at best there will be a lot more to this than meets the eye.

The avionics issue (which is what most people think of when they talk "IFR") is fairly trivial, and in any case could be sidestepped simply by installing the legally required IFR fit using certified avionics, which isn't exactly a lot of expensive stuff... a clapped out VOR receiver and I think that's about it

And an avionics fit which is truly useful for IFR (VOR, ADF?, DME, LOC/GS, IFR GPS, autopilot!!) is simply not going to feature in most homebuilts, due to cost and weight.

It is bizzare that clapped out 1970s iron can be IFR approved, but there we are... they got in by the back door, in the goode olde days, but this argument cannot be used to let other types in.

[englishal]

The Garmin 496 GPS-derived altitude is a helluva lot more accurate than an altimeter, especially with EGNOS.

Though I seem to remember something (from "satellite and Microwave systems & radio Navigation" from 20 years ago at University !!) about GPS receivers showing geodetic altitude or ellipsoidal altitude which uses a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. The problem is that in places like the Himalayas where you have lots of mass, this model creeps up above the true surface of the earth due to the additional mass. In some other places is becomes lower than sea level due to the opposite.

So I wouldn't trust the GPS altitude under 100' agl that is for sure!

[IO540]

Correct, but an IFR GPS contains (as a cert requirement) correction for this. It can be done with a polynomial but AFAIK most units do it with a lookup table which is interpolated.

At high altitudes, a GPS is potentially far more accurate than a baro altimeter because baro altimetry assumes things like the temperature gradient. One can often see this, by dialling the QNH of an airport one is overflying at say FL150; the GPS and the altimeter can differ by 500ft quite easily, while a GPS should be within say 20ft of the known airport elevation when on the ground (and better with EGNOS).

[Genghis the Engineer]

Even if GPS is more accurate, this is irrelevant. There are numerous standards that can be used to define altitude. Geopotential (GPS, very long ruler, being on top of a surveyed mountain...), pressure, temperature.

Everybody else uses pressure, so the airliners in the CAS just above you are setting altitude by reference to a pressure datum.

If that datum is causing them to be lower than would be "correct" by reference to a geopotential datum, then the arrogant PPL who thinks that his GPS is "more accurate" could well be inside what the airliner pilot believes to be his airspace.

The good news is that in all likelihood, only the PPL and his passengers will get killed by this piece of stupidity, or better it'll just result in a diversion, delay, several thousands pounds of extra costs, and removal of the PPL's licence - but since there's a risk that he might take 300 airliner passengers and crew with him, on the whole I think that he should be strongly encouraged to stick to using the pressure altimeter required by law to be fitted to his aeroplane.

G

[bingofuel]

I always thought the procedure when flying under a TMA was to set the QNH of the adjacent aerodrome. After all is that not why a TMA is there in the first place, to allow aircraft to safely manoeuvre in the area of the terminal aerodrome.

[Duchess_Driver]

I maybe an old fart - but am I the only person who would question the suitability of someone to hold a licence who states....

(with a view to 'illegally' flying in IMC).

Oh, it's okay, my medical only expired yesterday.

Where does this attitude eventually lead us?

[W2k]

And an avionics fit which is truly useful for IFR (VOR, ADF?, DME, LOC/GS, IFR GPS, autopilot!!) is simply not going to feature in most homebuilts, due to cost and weight.

It is bizzare that clapped out 1970s iron can be IFR approved, but there we are... they got in by the back door, in the goode olde days, but this argument cannot be used to let other types in.

Please, do explain what exactly is the problem with flying IFR in a bit of "1970's iron" (say, a PA-28) that has dual VOR, ADF, DME, LOC/GS, GPS and a KAP-100?

I'm a low hour PPL with a view to getting an IR at some point and of course the flying club I'm in has a bunch of ancient PA-28s from the 70's and 80's that are all flying along very happily, despite their age. Compared to a modern SEP like a Cirrus or Diamond, what, in your view, makes these old aircraft unsuitable for IFR ops?

[Pilot DAR]

but am I the only person who would question the suitability of someone to hold a licence who states....

No, you're not!

Happily, I have zero hours flying legal IMC/IFR in singles. I do have a few hundred filed IFR/IMC hours in properly equipped twins though, and that teaches me how happy I am to not have attempted it in singles. I do concede that in warmer parts of the world, IMC can be flown more safely in singles than here in Canada, but the possibility of airframe ice encounters, and failures in non redundent systems scares the heck out of me! Twice, I have survived in flight emergencies in IFR twins, which resulted from unforecast icing encounters. Several of my friends have not been so lucky.

My personal comfort level is that IFR/IMC in singles is a near emergency situation. Have I done it illegally? Yes. Was it planned, or a good idea? Never! It was done only because conditions had changed, or simply not ever had been forecast, and now I was there. For the most part, it was VFR on top (which at the time in Canada was still IFR). Instrument flight in cloud has the potential to be safer that scud running, but neither are a good idea in a single in my opinion. The only time I have ever had an artificail horizon roll over and die was within seconds of entering a cloud out of necessity, in a single. No dual systems, so some rather quick diagnosis to partial panel flying.

With a few exeptions, most light piston singles just are not designed for "hard" IMC flying. I agree that IFR filed for navigational convenience is generally not at all "hard" IMC, but you still have the potential to end up there! With a very few production singles actually being properly equipped for IFR these days, I think amature built aircraft are generally less likely to be so well equipped, tested and qualified.

My two cents worth...

[bingofuel]

Pilot DAR
I generally agree with your comment but am a little confused by your post. I may be misreading but are you advocating VFR on top in a SEP is okay, or was that one of the events that occurred due to unforeseen circumstances?

Okay, icing is not really an issue VFR on top, but other system failures could be, and you still have to descend through the cloud.

Apologies in advance if I misunderstood.

Duchess Driver
That has been my thought throughout this thread.
I am concerned that so many advocate deliberate violation of the rules. It does make you wonder about the airmanship of some licence holders.

[tmmorris]

Also, Pilot DAR, worth remembering that the typical British summer serves up lots of overcast/broken at 1500, tops at 2000 kind of weather, surface temperature 15-20 deg, so icing isn't a problem. In North America you are much less likely to be in IMC where icing isn't a factor, so a non-deiced single (which most are) would indeed be a bad option. Here, there is plenty of the year where a non-deiced single is still a useful IFR machine.

Tim

[Pilot DAR]

I may be misreading but are you advocating VFR on top in a SEP is okay, or was that one of the events that occurred due to unforeseen circumstances?

Over the span of my flying career, VFR on top in Canada has gone from being not legal, to legal, when properly rated, planned and equipped. I advocate flying within the regulations. That does not mean that sometimes things happen, but advanced planning to operate outside the regulations, your capabilities, and those of the aircraft, is just plain wrong.

So your standard equipped light aircraft has enough instrumentation that flight without reference to the ground is possible, but that does not make it safe or legal. There is usually a minimum redundancy designed into these systems, but you have to be a pretty sharp pilot on instruments (read IFR rating here) to manage well on partial panel, if you even recognize that's required after a failure.

I'm not saying that it cannot be done safely, there are obviously many who do. As the original question seems to have centered on amature built aircraft, I hold the opinion that they are one step further removed from the design requirements necessary for redundant systems, and truly safe IMC flight. That does not mean it can't be done, but I would expect that those who have a firm grasp of the practical, and regulatory requirements for the aircraft, probably would not be enquiring generally here (no disrespect intended to the original poster).

Climate plays a role in the circumstances conducive to icing, and I agree the summer in the UK is less conducive than Canada generally (though you are further north than I). That said, my second scariest icing encounter ever was day IFR in a Twin Otter southbound over Nice, France in August, during which we literally fell, while maintaining our attitude, through about 6000'. Yes, we had allowed swiss chees holes to line up, and thus were partly the cause of our circumstances, but it still happened fully legal IFR. Then, later in the flight, over Africa, where ice was not much of a risk, the instrument failures began. Flying an ILS down to minimums in a sandstorm, with nothing more than the magnetic compass for heading reference, is not too much fun either!

Last fall, while flying a Hughes 500D helicopter down from Alaska, I was reminded that fooling with the weather is a really bad idea in a poorly equipped aircraft. This helicopter had no gyro horizon or attitude indicator, no turn or slip indicator. It had a compass, ASI, altitude, VSI, and the engine instruments. That makes you think long and hard about what you need to be able to see in front of you in flight!

IMC is not to be tinkered with. Either stay out, or properly prepare, equip, train and file for the flight. I hold that generally light singles struggle to maintain the minimum of "equip".