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The GA planes I fly (with a club) have Garmin G5 PFDs. On these, the horizon/attitude indicator shows a few degrees pitch-up when in level flight. They're adjusted to indicate level on the ground based on the aircrafts' centerline, but in-flight changes in speed or W&B of course shift the actual attitude for level flight. This is kind of annoying when trying to develop instrument skills. The reason for this limitation for certificated aircraft (per Garmin) is an FAA regulation (14 CFR 23.1303(f)):

When an attitude display is installed, the instrument design must not provide any means, accessible to the flightcrew, of adjusting the relative positions of the attitude reference symbol and the horizon line beyond that necessary for parallax correction.

Never mind the "why" of this (it seems odd, but what do I know...). The above text is from a 2017 version of the code. (Actually published in 2011, per the GPO.) When I go looking for current versions on .gov sites, they don't exist. On the current gov eCFR website, I get this response when looking for that section:

The content you requested is no longer in the eCFR. It was removed on 2017-08-30, but the prior content can be viewed here.

There is a similar section of federal regs for transport category aircraft (25.1303) but it has no subpart (f) and says only that a bank and pitch instrument is required.

With all that windup, my question is: does this restriction on attitude indicators still exist? I cannot find a current version of the regs containing this restriction.

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    $\begingroup$ Closely related, perhaps even a dupe if your core question is about why 23.1303 is gone. $\endgroup$
    – Pondlife
    Jun 1, 2021 at 18:26
  • $\begingroup$ You indicate learning instrument skills, have you ever flown in real full IMC or all simulated/hood time?(it's not the same) Manually adjusting it in flight would defeat the whole purpose of a gyroscopic instrument. If the nose is slightly up it should show the nose is slightly up, it does not matter that you are in level cruise. If the pitch is up higher than normal in steady conditions that is an indication of something wrong, like slow airspeed(and a faulty ASI) There is no reason to just adjust that away and ignore it. $\endgroup$
    – Max Power
    Feb 25 at 21:57

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What the current rule is doesn't really matter relative to the G5. The G5 was certificated via an AML STC. The rules in place when the application for the STC was made were the applicable rules. The STC remains valid even if the rules change unless the FAA specifically includes in the new rule that previously issued certificates are rescinded (which is pretty rare.)

So as long as Garmin keeps building the G5, it has to be built to the existing design. If they make a major change to the design or start a new design, it would have to be to the current rules. Minor changes to a product can be made without a change to certification basis.

With the new 'performance based' rules, it would be difficult to predict result of the certification process for a new product. It's the manufacturer's responsibility to design the product and show that it meets the rules.

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  • $\begingroup$ My understanding is that the G5 for “experimental” aircraft doesn’t carry the limitation on adjusting the horizon indicator. So they already have these things as part of their production process (presumably differing only in software). Are you saying that if they wanted to deviate in even this seemingly small way from the STC they’d have to go through a new certification? (It would sure be nice to be able to adjust the thing in flight.) $\endgroup$
    – Foster Boondoggle
    Jun 2, 2021 at 2:29
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    $\begingroup$ They would have to amend the STC at a minimum. Even with the new rules, they would still have to address the function in their system safety analysis (SSA). They old rule existed to address some perceived hazard, so you couldn't just say it isn't a concern because it isn't in the new rules. The new rules still require you to address the hazards, they just don't tell you how to do it. In any case it isn't a small impact. It affects manufacturer's that buy the G5 as they'll have to amend their TCs, spare parts substitutions, documentation, etc. And it's unlikely to affect sales. $\endgroup$
    – Gerry
    Jun 2, 2021 at 11:57
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The FAA rewrote 14 CFR Part 23 entirely at the end of 2016, and those changes went into effect August 30, 2017. You can find a discussion of the changes made in the Federal Register at 81 FR 96572. The current standards are in the new 14 CFR Part 23, which I find easiest to browse on ecfr.gov.

Based on my reading (I am not a lawyer, I am not your lawyer, and I'm not an aircraft mechanic), it looks like the restriction you asked about was deleted. This seems to comport with the general purpose of the Part 23 overhaul, which replaced "prescriptive design requirements with performance-based airworthiness standards." (Quoting the summary of 81 FR 96572.)

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