That looks very good. There is a lot of detail involved and I am not sure this pilot quite understands the interconnections. It also sounds like he might be using the GTN750 as the GPS for the GI275.
Interesting that Garmin have just fixed some issues in the past days…
The other interesting angle here is that it frees the vac pump drive and you can put a B&C 410 backup alternator there. That’s a good thing otherwise you will lose the autopilot when the GI275 battery goes flat.
Yes, a 2nd alternator instead of the vacuum pump is interesting to me as well, given that the electric buses in my plane weren’t really designed for a glass panel. Your 337 has been mentioned in this context over on MooneySpace.
You will lose your autopilot well before the GI275 battery goes flat.
You will lose your autopilot well before the GI275 battery goes flat.
How?
Is this a competition for making posts which always require clarification?
I wish people who do this (obviously deliberately) found some other forum for that sort of thing. The internet is big…
2nd alternator instead of the vacuum pump is interesting to me as well
Sadly unless you can make use one of the B&C STCs, it is always a Field Approval. I used a good guy in the US for mine so if anyone needs his details…
For an electrical engineer it shouldn’t require clarification. The GI275 battery kicks in once the ship power source is exhausted and lasts for one hour.
Unless your navigator and KFC come with a discrete standby power source and each servo has an independent emergency power supply, the autopilot will cease functioning long before the GI275 does.
I think what is being said is that the GI275 internal battery only kicks in once all of ship’s power sources go offline, thus rendering the AP offline. Hence you loose the AP due to lack of electricity before the internal battery on the GI275 ever kicks in.
I know the 2ndary alternator is done via a field approval, but M20K’s have already been done and there is a 337 floating around. B&C were supportive in making it happen.
Once the GI275’s battery is exhausted, you can’t fly in IMC, so may be unable to land. You are therefore looking at an emergency situation as soon as the alternator fails. You need to land within 1hr, plus how long you think your aircraft battery will last (30 mins?). Could be “fun”.
Whereas with a KI256, or with a 2nd alternator, you can continue the flight.
Indeed; you can use a Field Approval as approved data for a Field Approval. You still need an FSDO to approve your Field Approval, however 
Only an STC, or a DER 8110 exercise, gets around the need to involve a US FSDO.
tmo wrote:
I know the 2ndary alternator is done via a field approval, but M20K’s have already been done and there is a 337 floating around. B&C were supportive in making it happen.
Many 252s came with a second alternator as a factory option, mine as well. Isn’t I possible to sign it off “as per Mooney drawing xxx” in the log book by an A&P?
EDIT: I mean an original one, not a B&C one which would be better…
You can use a Type Certificated mod as data for a Field Approval, for an STC application, etc, sure.
If there is a TCd mod and you plane is the right model and within the airframe S/N range etc then you can just install that mod, as per the TC installation, with just a logbook entry. This is normal in the US but predictably there is a range of opinions on that in Europe
Mine is a 231, not a 252, so a different engine variant; the Service and Maintenance Manual, it says: An optional standby generator (12V, 10 amp) is available to operate basic essential components in the event of main alternator failure on S/N 25-0613 thru 25-0999 aircraft. An optional second 70 ampere, belt driven alternator will be available on S/N 25-1000 and ON aircraft. Mine, being 25-0396 doesn’t qualify, but maybe the fact that I have the -LB engine (sn 25-0781 thru 25-0889) will help. Might also be related to 12V vs 24V. Making a note for when I actually need this.
Either way, I don’t think it will be a major challenge on a N-reg, with paperwork available and the path already tested by others.
