Please give advice if you can. My D180 is reporting the altitude to my Garmin transponder almost exactly 500-feet too low. ATC allows up to 300-feet disparity, so they are requiring that I turn off "altitude" reporting and report altitude by radio. (Not sure how long they will show this much grace.) The avionics shop tell me their testing does not show the inaccuracy, but still showing low to ATC and tower. My hunch is that there must be some setting in the D180 that we are overlooking since the unit itself reports the altitude accurately...it is just the relay to the transponder that is off. Thanks in advance for any hints. ps: I had an A&P install the units and the avionics shop try troubleshooting, problem is neither is all that familiar with the D180.
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D180 reporting wrong altitude to GarminTransponder
- Thread starter rodlueck
- Start date
Re: D180 reporting wrong altitude to GarminTranspo
You did not mention what kind of transponder you have and what connection method you are using. Either serial or gray code?
If it is serial, your EFIS spits out exactly what the alt. will show when you set it to 29.92"
If gray code, I would bet that you have one wire with a bad connection or shorted to ground. It only takes one to screw up gray code.
You did not mention what kind of transponder you have and what connection method you are using. Either serial or gray code?
If it is serial, your EFIS spits out exactly what the alt. will show when you set it to 29.92"
If gray code, I would bet that you have one wire with a bad connection or shorted to ground. It only takes one to screw up gray code.
- Joined
- Mar 23, 2005
- Messages
- 13,226
Re: D180 reporting wrong altitude to GarminTranspo
A few things:
Which xponder? What kind of connection? If gray code, a single wire broken between the encoder converter and your xponder can cause altitude innacuracies.
If serial, it's practically impossible for the EFIS to not be reporting the altitude correctly, at least as far as it knows is correct.
If you can set your baro setting to what airport ATIS/ASOS claims it is, and field elevation is then displayed correctly on your EFIS display, then your altitude calibration is fine. If you need to move the baro setting around a LOT to get the display to match field elevation, then we might need to recalibrate your unit. If your EFIS was off by 500 feet, you'd need to dial in another .50" on your baro setting.
A few things:
Which xponder? What kind of connection? If gray code, a single wire broken between the encoder converter and your xponder can cause altitude innacuracies.
If serial, it's practically impossible for the EFIS to not be reporting the altitude correctly, at least as far as it knows is correct.
If you can set your baro setting to what airport ATIS/ASOS claims it is, and field elevation is then displayed correctly on your EFIS display, then your altitude calibration is fine. If you need to move the baro setting around a LOT to get the display to match field elevation, then we might need to recalibrate your unit. If your EFIS was off by 500 feet, you'd need to dial in another .50" on your baro setting.