Steam attitude indicator changes after pitot-static check

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danno2000
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Steam attitude indicator changes after pitot-static check

Post by danno2000 »

Hi all -
My plane's a 2003 DA-40-180 with steam gauges. Went to have the 24-month pitot-static check done. Passed inspection.

But on the flight back, the indications from my attitude indicator were different. Overall it seemed to indicate more of a nose-down attitude than normal -- it was turbulent so wasn't easy to tell in straight-and-level flight, but it didn't seem like a big deal until I got into the traffic pattern at my home airport. The AI showed 10-degree down angle on downwind with takeoff flaps set, and then was briefly more than 10 degrees down on deploying landing flaps. I'd say usual AI reading would be down 5-10 throughout the approach. On the ground, indicates flat as expected.

I'll have to do an instrument approach somewhere else to be absolutely positive that the readings are different from what they were before and by how much.

Mech says he's never seen anything like this. First time I've used the guy but had good local reviews.

I usually fly by myself with minimal baggage so it's not unusual for me to have trim set nearly full nose down in cruise. So I'm even wondering if the new readings are actually closer to correct than the old ones were.

Any thoughts much appreciated!

thanks,
dan
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Rich
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Re: Steam attitude indicator changes after pitot-static check

Post by Rich »

There's no input to the original AI from the pitot or static lines. Just power from the essential bus and leads to the instrument light. I assume it's still bolted solid to the instrument panel and the "cage" knob isn't pulled out. AFAIK there isn't any adjustment possible to the vertical alignment unless it's something hidden on the back of the casing. It's possible that the unit is starting to wear out. This has happened to others and would seem inevitable.
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danno2000
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Re: Steam attitude indicator changes after pitot-static check

Post by danno2000 »

Rich wrote: Wed Apr 28, 2021 3:34 pm There's no input to the original AI from the pitot or static lines. Just power from the essential bus and leads to the instrument light.
I was almost positive of this. But the coincidence of it happening only right after the inspection seemed odd.

Guess it's time to start looking at G5s.

thanks,
dan
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Steve
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Re: Steam attitude indicator changes after pitot-static check

Post by Steve »

I can't imagine that there is anything behind there to disturb that would cause this. The AI has a single 4 wire connector (per, and, 2 lighting). If that were loosened, you would have an INOP flag. I'm looking at my (removed) one right now, and there are no external adjustments whatsoever.

When you cage it, does is cage to zero pitch and roll like it should?
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danno2000
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Re: Steam attitude indicator changes after pitot-static check

Post by danno2000 »

Steve wrote: Wed Apr 28, 2021 5:39 pm When you cage it, does is cage to zero pitch and roll like it should?
Yes, caging works fine and afterward indicates flat and level. In flight, bank angles seem consistent with past practice. Climb-out angle seemed right as well. It's only the down-nose angle indication that seems out of place. And after landing, it indicates flat and level as you'd expect.

It's enough to make me second-guess whether it wasn't always this way and I just didn't notice. But seeing a down 10+ degree angle on what I consider a normal-steepness pattern into my valley-bound airport looked wrong. I'll have a better idea when I go to Albany and shoot the ILS there because I have all the standard instrument approach speeds and settings pretty much in muscle memory.

thanks,
dan
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