DA42 experimental autoland

But I was thinking of this Da42 only which does not need to be able to glide anywhere.

It would depend on why both engines stopped… on the MEP scene it is usually due to the volume of air in the fuel tanks gradually becoming equal to the tank volume

But you could also get contaminated fuel. Deliberately perhaps.

I frequently see some odd read outs on the Garmin 1000 that are obviously wrong, must be some kind of averaging calculation?

In what circumstances? That should not happen with GPS unless you lose reception, or there is military-grade jamming.

Oh ok… the wind vector calculation becomes progressively more sensitive as the heading approaches the track and/or as the TAS approaches the GS.

If your slaved compass system is say 2 degrees off (easily possible; it’s damn hard to get it a lot better) and your ASI is say 2kt off (more common than not) and the OAT probe is say 2 degC off, the wind calculation will be way off unless the wind is so strong it is blindingly obvious where it is coming from.

If you think about it, a plus or minus 1kt error in the ASI, against a constant GS, and the wind is only say 1kt, this will swing the wind vector from 180 to 360, or something like that. But the reality is that this is “dead calm”.

OTOH one could argue that the wind vector hardly matters if it is light enough… it’s just that we humans expect a $10,000 feature to work perfectly

Another thing is that the airdata computer may not be getting heading changes fast enough as you do a turn. A directional gyro like the old KG102A can lag a bit, and an ADC fed with the heading in the old X/Y/400Hz interface isn’t going to respond as fast as if it is an AHRS gyro putting out ARINC429 at 30 or whatever packets per second. They had a similar problem in TCAS systems in helicopters, where the heading data lag made it work poorly if you swung the thing around a bit too quickly…

1 degree is almost impossible to achieve, because even a metal hangar 300m away will affect the field by that much.

And the aircraft electrics affect it by maybe more… whether the battery is being charged, whether the pitot heat is on, etc.

Errors in the field are not part of the above error limit I’d say.

True, but when you are calibrating any aircraft compass system, you have somebody with a big fancy handheld compass standing maybe 50m away, lined up with the nose, and making hand gestures to you so you can drive it around onto the new heading. Or some variation thereof.

So it’s likely the two compasses won’t be seeing quite the same field.

it would be intriguing to see how the course guidance is smoothed-out.

With a good AHRS, perhaps?