Loss of GPS does not affect attitude provide pitot remains available
That’s the exact issue though, isn’t it?
I’m still lurking😉
The GI275 does use pitot-aiding as well as GPS. I’ve recently done practical testing of this on a fast jet and seen the failure modes. Loss of GPS does not affect attitude provide pitot remains available and IAS is below 425 knots. Above 425 kts and with GPS lost, the attitude will coast (gradually degrade) and will indicate failure and go into realign after about 6 minutes.
I think @wigglyamp has moved on or maybe nobody flying in the UK with a GI275 who has tested this aspect. And any garmin dealer who knows the answer won’t be posting it unless it is affirmative.
This is another approach:
For amusement (no STCs):
The Garmin GI275 is a fully certified replacement for the KI256 and STC’d on multiple aircraft so it can be done successfully without lots of external interface boxes. But as suggested, it does require a GPS input and has internal air data computation.
@wigglyamp is the GI275 vulnerable to loss of “airdata” (whatever that means)?
I’m going with the rather more rough and ready (and most importantly – in my lab!) Edwards roughing pump with an adjustable valve on it to ensure I don’t blow the 256 to pieces. First test showed a perfect shake-out and straight and level attitude on the bench. Next step is to pop a gauge in there and set the valve to deliver 5 in.
The motor on mine is a dirt cheap motor which is all over Ebay. Search for
single phase motor
They are nearly all chinese and incredibly cheap. They all run at ~1300rpm; it’s the most you can physically do with 50Hz Don’t get one any smaller than mine; the vac pump needs a lot of torque. Mine says 90W.
And a chucked out vac pump will do just fine.
The vac gauge comes from a car parts shop which sells gauges for tarted-up cars (alongside 500 watt sound systems and all the other stuff boys without girlfriends out in their cars ).
I got the replacement from a parts business in the US and it can be returned so I think I’m OK on that score. Also after digging it turns out the original one was ‘repaired’ at SIBA in 2015 and only has about 300 hours on it. I have no indicator, just a low vac and high vac annunciator. I’m going to make up a 5 In Hg vacuum rig in work today thought it will be rougher than yours!zuutroy wrote:
Do you have a working vacuum indicator?
Certainly there could be a problem with the vacuum but to have both that, and a defective indicator which is not showing it, would be surprising. I have a vacuum pump but it would be a big thing to ship to Ireland
OTOH it is possible somebody scammed you. IME a good % of used avionics does not work and the seller knew it. I bought a “unused” SG102 3 years ago and when I installed it it showed intermittent errors when turning fairly fast, and it turned out it has been back to Sandel several times for an “overhaul” which was evidently a factory test which always passed, on the bench, hey ho, hey ho. I did get an unused fluxgate with it though.
I got my hands on a different 256…It too won’t even erect during a ground run. Something funky with the vacuum system post overhaul?
I don’t suppose anyone has a 0 degree tilt 256 with mod 11 that would be surplus to requirements? They’re not so easy to come by.