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.