Struggling to understand the KAP 140 and BARO settings

Hi, I’m flying the Cessna 172S with G530/430. I’m having trouble understanding why the autopilot instrument (KAP 140) isn’t in sync with my altimeter.

For instance I set my barometer steam gauge to 30.18 per ATC instructions. I then go to the autopilot press BARO button, then hold it down to get “in hg” readings and set that to 30.180.

I climb to 8,000 ft and ATC tells me I’m either 300 to 400 feet over my assigned altitude. I then have to change the autopilot to 7,700 to correct the problem. Can you help me understand how to properly set this instrument? Thank you.

Not sure if this bug post is related:

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Hey there,

I was struggling with the same issue and yes apparently (from other members) it’s been a bug with the KAP 140 since release.

Even when setting the BARO in the KAP 140 and the Altimeter to the same, it still falls out of sync.

For “realism” I still update them both, but then I hit the “B” key on the keyboard to sync up the back end.

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For a reason only the developers know there seem to be several barometric pressures or altimeters in this sim. Some we see, some we don’t. What you do with the altimeter calibration (Kollsman window) and the KAP140 is how it should be done if it was done correctly. But since this sim is a huge buggy mess, no need to express it more politely, we indeed have to press B everytime we want all the altimeters or barometric sources to be calibrated to the same source. In the case of this sim it’s always 1013hPa/29.92 inHG above 18000’ around the whole world and the QNH below that altitude. However as there are sources in the background that won’t be synchronized to what you dial in the AP will always be off. So as said before, press B and forget doing it the correct way.

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“B” is your friend. Press it often, or after every ATC call that includes a Baro reading, even if it’s not directed at youm

The “B” key is nice, but I’m on the #xbox so that’s not happening. :grinning_face_with_smiling_eyes: Now that I know I’m doing it correctly; I don’t feel so bad when it happens. It’s a little weird, but I do enjoy having to make calculations while flying.

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You should be able to bind a button to it. You could also plug a keyboard in :slight_smile:

Whilst there probably is a bug in the KAP140, remember that ATC only sees your Transponder reported altitude, which is always in standard setting… which can easily account for a 300 feet difference

Oh my transponder. I didn’t think about that. It makes sense though. I’ll keep an eye on that while troubleshooting.

Do you mean real life transports report based on standard setting, or do you mean that in the sim, the transponder reports based on standard setting? Do you have a source for your statement handy so I can read more?

In real life all transponders that can report altitude (mode C and S) report pressure altitude (1013hPa/29.92inhg)

I suppose the sim will do the same but I am not sure

Use standart qnh 1013/29.92 at or above transition altitude and QNH decending through transition layer or below transition altitude.
(Or QNH in decent when no level off before transition level, also in mountinious areas qnh is used above transition altitude)

Reason is to let fly everyone wrong in the same way. Since True altitude is varying according to the the actual pressure(and temperature)

I do have a keypad for my Xbox controller. To my surprise the B key worked just fine. So; I’m setting the Altimeter, manually, then pressing B to sync up the KAP 140. Works like a charm.

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