ATC in-air "discussion"

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Rich
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ATC in-air "discussion"

Post by Rich »

My altitude encoder has a known discrepancy with my altimeters of +100 ft. This is actually within allowed tolerance, but it causes a couple of issues:

1. When using altitude pre-select or ALT hold, I set the autopilot 100 ft. higher than desired. e,g, set 8100 ft to level/hold 8000 ft.
2. When flying at a given assigned altitude (with or without AP engaged) ATC will see me as 100 ft. higher than assigned.

The latter has sometimes resulted in real-time "discussions" with ATC. Last Sunday while departing Pearson field (Vancouver, WA) beneath the PDX Class C as PDX tower insisted I was at 900 when I reported at 800.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Diamond_Dan
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Re: ATC in-air "discussion"

Post by Diamond_Dan »

What would it take to "fix" the problem and how much does it cost?
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Rich
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Re: ATC in-air "discussion"

Post by Rich »

At least for my encoder, the Sandia SAE5-35, there is a straightforward procedure for adjustment. It's best done in conjunction with the 24 month transponder check, which tests the correlation of the Density Altitude being broadcast with the altimeter(s). There are a couple of buttons accessible from the side of the unit to do this. I've just kind of lived with it, since it's technically within spec (+/- 125 ft with the primary altimeter) and fully repeatable and constant offset at all altitudes. My recheck isn't due for a few months but I'm thinking I'll get it done earlier to avoid these annoying in-flight discussions.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Rich
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Joined: Mon Aug 30, 2010 12:40 pm
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Re: ATC in-air "discussion"

Post by Rich »

This excerpt from the Sandia manual shows the adjustment buttons that need tweaking:
Sandia Adjustment.png
Sandia Adjustment.png (86.74 KiB) Viewed 520 times
Here's how one gains access to these things in my plane. A challenge to say the least:
Encoder Adjustments.jpg
Disclaimer: Diamond has produced a number of different instrument panel designs over the years so the location and even the encoder model in mine might not be the same as others.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Steve
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Re: ATC in-air "discussion"

Post by Steve »

Rich is correct on the mounting and model variability. Mine has a Trans Cal encoder, which is not adjustable, and is mounted in an equally inaccessible area…
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