In stabilized cruise flight, at standard cruise power settings, my primary, factory attitude indicator shows the airplane on the horizon line. The GI275 ADI page shows the aircraft symbol about 2.5 degrees nose-up. I’m wondering if the GI 275 has to be calibrated when straight and level, like the ADHRS display in ForeFlight does.
GI275 question
- Thread starter TBalch
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Is the factory AI vacuum driven with the knob on the front that adjusts the little airplane? When you adjust it on the ground, do you set it to the horizon line? What is the actual attitude of the plane when you do that? What does the GI275 indicate when you do that?
WannFly
Final Approach
my G5 shows 2.5 degree nose up in the air too with VS = 0, you just cant see it in the old vacuum driven AI unless it has been calibrated like asicer pointed out. even after that its very difficult to notice in air. I am glad that 20 year old AI is now gone
Ryan Klems
Line Up and Wait
This is a common complaint among folks converting to glass instruments. They are used to being able to adjust the "aircraft" on the horizon on a vacuum/pressure AI. The reason this adjustment is present is parallax. Because the horizon and the indicator are in two different planes, adjusting your seat higher/lower, being taller or shorter in the torso, etc, you will see different positions, so there is an adjustment for it. With glass, there is no parallax because the everything is in the same plane. The FAA regs only allow for parallax adjustment which is why there is no zero adjustment on these glass instruments. The calibration steps for these instruments typically call for it to be done with the aircraft leveled per the MM. That level is _not_ level flight level. This will vary based on gross weight, center of gravity, etc. Depending on the aircraft and loading while flying straight and level you may have nose down relative to the horizon, or you may have nose high. This is perfectly normal. Some folks get really bothered by this and go about messing with settings to try to get it to read on the horizon while in some variant of level flight. I personally don't recommend that.
FAA Reg about this:
§ 23.1303 Flight and navigation instruments.
(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.
FAA Reg about this:
§ 23.1303 Flight and navigation instruments.
(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.
I had the same issue on my G5 that I noticed immediately after install. About a week later, I returned to the shop for a few minor squawks and they were able to adjust it. You should return to the shop, or any other Garmin shop and have this corrected. I know I wouldn't want to be inside a cloud and see a discrepancy between my attitude and VS.
I would assume that the GI 275 would have a similar adjustment.
chemgeek
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If you have a certificated G5 (and I presume a GI275) it is by the installation manual to be adjusted so that it reads zero degrees when the plane is level as per the maintenance manual. And you must disable the horizon adjustment feature on the unit. At cruise, you will likely find that level flight is not zero degrees attitude. On my AA-5, level flight is about +1.5 degrees. A cruise descent is about -0.5 degrees. Approach configuration for level flight at 90 kt is +2.0 degrees. This is not a problem flying IFR. You just need to know the appropriate flight attitudes required for your pitch+power numbers, and of course cross-check level flight with the altimeter and VSI.
If using non-zero pitch/power settings in cruise is unacceptable, the installer can make an adjustment of the pitch correction to better conform to zero degrees in level cruise flight, but the the horizon adjustment feature must still be disabled for certificated aircraft installation. The electronic gyros are so accurate and easy to read without parallax that you have to learn new pitch/power combinations for various flight regimes anyway. I used to fly the mechanical gyros by "dots" up or down (which was always a gross approximation due to parallax) but the electronic displays can be precisely flown by degrees up or down.
Groundpounder
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John Myers
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As others have said, zero degrees in cruise is an arbitrary and changing value that depends on weight, etc.
Calibrating your AI to zero degrees during cruise is sort of like calibrating your angle of attack indicator to zero during cruise. If you had them change this to zero at some arbitrary cruise configuration your AI is now wrong, as far as how the FAA/Garmin/aircraft manufacturer intend it to read. The plane should be leveled to zero degrees pitch per the manufacturer and the AI set. You can then compare your pitch to others in the same type (ex: 10 degrees pitch up during climb, etc.).
Calibrating your AI to zero degrees during cruise is sort of like calibrating your angle of attack indicator to zero during cruise. If you had them change this to zero at some arbitrary cruise configuration your AI is now wrong, as far as how the FAA/Garmin/aircraft manufacturer intend it to read. The plane should be leveled to zero degrees pitch per the manufacturer and the AI set. You can then compare your pitch to others in the same type (ex: 10 degrees pitch up during climb, etc.).
Aviator305
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I have learned to fly as prescribed in Positive Flying, and it has worked really well for me. I consider these instruments to be tools to be used as we each see fit, and I wish there was some flexibility afforded to us by the manufacturers. If I could not adjust the “zero” to level cruise attitude, I would truly miss that capability afforded by my old attitude gyro.
chemgeek
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Having transitioned from vacuum gyros to dual G5s, it's just not an issue for IFR flying. You simply have to learn new "numbers" for various flight regimes. Then you are done. The G5s actually make the "numbers" more reproducible because they are so precise, always report absolute attitude relative to a constant reference, and do not have parallax issues.
Aviator305
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Right. So, I would have to learn new numbers just because there is no provision to make a small adjustment.
There’s nothing wrong with flying the way you say, but there’s nothing wrong with the way that I grown accustomed to flying either. I like having mine attitude reading zero when I am flying straight and level so that I can then instantaneously eyeball if I am one or two needle widths of the horizon (which corresponds to predictable performance for a couple of power settings).
Different strokes for different folks.
Nah. Just install a GFC500/GFC600 and turn on the FD bars.
WannFly
Final Approach
Are you saying no matter what the weight is or the power setting is, your attitude reading is zero? That doesn’t sound doable
Aviator305
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I nearly always cruise at the same power setting with similar-enough weight. It works very well! Sure, it can be off slightly, but never an entire needle width or even really anything very perceptible, at least not in my experience in my plane. If I start using different power settings, of course everything gets thrown out the window.
John Myers
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I’d agree that for most small GA aircraft it’s not a big deal if the reference is something other than what the manufacturer intended, as you say for the old style AIs it wasn’t really possible to do that anyways. I can see both sides of it, but I don’t think it’s fair criticism to say that, now that we do have instruments that can be set precisely, that they should also be able to be set what is technically incorrectly so folks don’t have to learn a different (and now standard) pitch reference.
Aviator305
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It’s not incorrect. It’s simply a matter of preference. Do you zero at level attitude at the ground or at level flight? It should be up to the pilot. I find that saying one is correct and the other incorrect somewhat of an authoritarian attitude.
Kent Wien
Pre-takeoff checklist
Well, Boeing and Airbus don’t give you a feature to ‘zero’ out the pitch attitude. The zero point is constantly changing with flap setting and speed.
But, what you are really asking for is a Flight Path Vector indicator, which you can display on the Boeing and Airbus. I’m not sure if Garmin offers that. It’s slick. You put the little vector symbol (a small circle with tiny stick wings and a rudder) on the horizon and you are level regardless of airspeed or configuration.
Edit: I just looked it up. Garmin has included the Flight Path Vector in the GI-275! Problem solved.
But, what you are really asking for is a Flight Path Vector indicator, which you can display on the Boeing and Airbus. I’m not sure if Garmin offers that. It’s slick. You put the little vector symbol (a small circle with tiny stick wings and a rudder) on the horizon and you are level regardless of airspeed or configuration.
Edit: I just looked it up. Garmin has included the Flight Path Vector in the GI-275! Problem solved.
John Myers
Pre-takeoff checklist
It’s not correct per the aircraft maintenance manual, the FARs, and Garmin’s installation manual. This one isn’t up to preference, technically speaking. It’s impossible to set it to zero in level flight because your pitch will always vary depending on weight, power, etc.
Aviator305
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What FAR says that I can’t level set my attitude indicator to whichever way I find most useful? If this is true, I would find it surprising given fact that a well respected book was written flying with this technique.
Aviator305
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Exactly. I just ran into a video showing the flight path marker on the GI-275 just as I read your post. Very nice. I would not miss my manual leveling capability with this feature activated.
Ryan Klems
Line Up and Wait
See my post above:
§ 23.1303 Flight and navigation instruments.
(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.
WannFly
Final Approach
I think what John is saying is the way you have it set up, it shows 0 attitude only under one very specific situation. so what happens when you are in IMC, ATC asks you to slow down, you pull power, the nose goes up but you are level with VS = 0. i am guessing you train yourself to ignore the attitude indicator then and rely on VS and altimeter to judge if you are climbing or not. vacuum gyro and EFIS are two different things, no point trying to make EFIS work like gyro. but hey, if it works for ya, have at it. the installer will install based on A/C install and mx manual and follow direction as provided by manufacturer.
i havent read the book you reference, but if its written keeping vacuum gyro in mind, it might not apply to EFIS directly
Aviator305
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This does not exclude the operation of the attitude indicator in the manner in which I and others that I know use it. This FAR does not define the zero level.
At any rate, I really do not wish to debate this point. I know that others use the technique I use, because I am not the originator of this idea. I picked up on it because someone that I respect recommended the above book, and the philosophy works very well for me. Everything can work under ideal circumstances, but in the soup performing a go-around, minimizing variables is a desirable goal and I believe that the technique prescribed in said book is optimal. The FD bars that I just learned on the GI-275 look like a superior substitute to flying with this technique which is indeed aimed towards analog attitude gyros. If I were to replace my analog instruments, the GI-275 would be at the top of my list now that I see this working.
John Myers
Pre-takeoff checklist
That’s in reference to an analog AI with a movable bar. You’re talking about asking a Garmin dealer to make modifications to an AI counter to the install instructions. I’m not bashing you for doing it, but on the point of if it’s technically correct, it simply isn’t.
I don’t care enough to find the relevant FARa beyond that one (I think it’s in part 23), but clearly this would be dangerous in some situations if a pilot flew by pitch reference and the plane did things it shouldn’t do at that pitch. Again, for small GA aircraft, or one only you fly, I don’t think setting it up counter to the way it was intended presents any serious issues.
Ryan F.
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Many of us who flew behind mechanical attitude indicators over a very long period of time (raises hand) became accustomed to adjusting the "attitude reference symbol" to be superimposed on the horizon line in cruise flight.
But, that wasn't really what it was for. The purpose of this adjustment is just for parallax (thanks for the part 23 reference, Ryan) w/r/t seating position, pilot height, etc.
The attitude indicator indicates the attitude of the aircraft, not its flight path. Most commonly, airplanes will have a slight nose up attitude even in cruise flight. A properly calibrated attitude indicator reveals this. The Bombardier and Gulfstream products I fly (all/mostly glass flight decks) do in fact show a slight nose up attitude at cruise on the PFD. Obviously, the higher the speed, the lower the delta between the horizon line and the reference symbol.
If the ADI is properly calibrated, and showing you a nose up attitude, that is the attitude of the aircraft and you should not want to adjust it just based on a comfort factor. There's a reason it's not to be adjusted on electronic attitude indicators. It is, after all, there to indicate your actual attitude. You don't want it to indicate something else.
But, that wasn't really what it was for. The purpose of this adjustment is just for parallax (thanks for the part 23 reference, Ryan) w/r/t seating position, pilot height, etc.
The attitude indicator indicates the attitude of the aircraft, not its flight path. Most commonly, airplanes will have a slight nose up attitude even in cruise flight. A properly calibrated attitude indicator reveals this. The Bombardier and Gulfstream products I fly (all/mostly glass flight decks) do in fact show a slight nose up attitude at cruise on the PFD. Obviously, the higher the speed, the lower the delta between the horizon line and the reference symbol.
If the ADI is properly calibrated, and showing you a nose up attitude, that is the attitude of the aircraft and you should not want to adjust it just based on a comfort factor. There's a reason it's not to be adjusted on electronic attitude indicators. It is, after all, there to indicate your actual attitude. You don't want it to indicate something else.
Aviator305
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Juan
Those aircraft have flight directors?
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You must have a lot of trouble with other aspects of our heavily regulated aviation activities then.
Ryan Klems
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FYI, FD (flight director) bars are going to come from your autopilot, so you'd need to have an AP capable of providing them to have them displayed on the GI-275. The flight path vector (separate indication) requires the synthetic vision unlock (and a 3D GPS position fix) for it to display.
chemgeek
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Exactly. Attitude in level flight at 70% power won't be the same as level flight at 65% power won't be the same as level flight at approach speed. Putting the AI at zero degrees at cruise doesn't guarantee level flight in every flight regime. You are in level flight when the altimeter is constant and the VSI reads zero. What the AI says at that time is the appropriate attitude. Flying by the numbers means knowing what those numbers are. When you can adjust the AI in flight, the attitude setting loses absolute meaning. So if level flight at 65% power is zero degrees at 2500 rpm, then level flight at approach speed CAN'T also be zero degrees at 2200 rpm. And then your missed approach climbout will be...what? If it is 10 degrees nose up at full power, is that 10 degrees based on level cruise flight being zero degrees, or 10 degrees based on zero degrees for level flight at approach speed, or 10 degrees based on zero degrees sitting on the runway? Having an absolute reference point adds precision to one's power/pitch settings, and is a step way ahead of the mechanical AI gyro instrument which was difficult to display precise attitude in the first place due to significant parallax errors. New instruments, new procedures. I now better understand why when I trained 30 years ago why the AI always needed "adjustment" for level flight when I slowed to approach speed, or leveled off at cruise after initial climbout.
OC59
Filing Flight Plan
I know this is an old post, but since I stumbled on the thread while searching around on exactly this issue, I want to chime in about whether the GI275 restriction is regulatory. I believe that as of August 2017, that regulation no longer exists. If you look for it on an official .gov website, you will find old (pre-2017) versions of the code, but it appears that essentially all of part 23 was revamped that year. Quoting from a recent response on stackexchange:
> 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. ... Based on my reading ... it looks like the restriction ... 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.)
So the ban on adjustments "other than for parallax" no longer exists, though another commenter on that same stackexchange thread said (roughly) "it must have been there for *some* reason so even on an application under the new regs the manufacturer would have to explain why allowing the adjustment doesn't cause a risk".
> 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. ... Based on my reading ... it looks like the restriction ... 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.)
So the ban on adjustments "other than for parallax" no longer exists, though another commenter on that same stackexchange thread said (roughly) "it must have been there for *some* reason so even on an application under the new regs the manufacturer would have to explain why allowing the adjustment doesn't cause a risk".
Der Fliegermeister
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The conversation should've been over after @Ryan Klems posted his response.
Preferences and opinions are simply never going to be reason enough to deviate from an STC, which specifies (read: requires) the aircraft to be leveled and the attitude calibrated to that pitch. It also requires the installer to disable the option to adjust it.
Think of it this way: when a controller asks you to maintain 3,500 and 80 knots, what's your attitude indicator going to look like? Not level, I promise.
If you break into your configuration settings and enable the adjustability of your G5 or 275 etc and then bring it to me for an annual, I will squawk it and disable it again. Yes, I check all configurations for compliance at annual. I'm covering your a$$ the same as mine.
This way, when your anti-authoritarianism kicks in and you start flying around at night with an ADI that no longer complies with the STC, manufacturer's installation documents, or...THE AFMS, because you messed with it...and you bend your airplane... I can show the NTSB that I corrected the issue when I worked on it and I can prove beyond a reasonable doubt that you noodled with configurations after I signed it off. And if I find it twice from the same owner, I'll never work on their stuff again.
This is not a debatable topic. The regs are black and white. Anybody suggesting it's a matter of preference is openly advocating that you willfully break a regulation, whether you know it or not.
Preferences and opinions are simply never going to be reason enough to deviate from an STC, which specifies (read: requires) the aircraft to be leveled and the attitude calibrated to that pitch. It also requires the installer to disable the option to adjust it.
Think of it this way: when a controller asks you to maintain 3,500 and 80 knots, what's your attitude indicator going to look like? Not level, I promise.
If you break into your configuration settings and enable the adjustability of your G5 or 275 etc and then bring it to me for an annual, I will squawk it and disable it again. Yes, I check all configurations for compliance at annual. I'm covering your a$$ the same as mine.
This way, when your anti-authoritarianism kicks in and you start flying around at night with an ADI that no longer complies with the STC, manufacturer's installation documents, or...THE AFMS, because you messed with it...and you bend your airplane... I can show the NTSB that I corrected the issue when I worked on it and I can prove beyond a reasonable doubt that you noodled with configurations after I signed it off. And if I find it twice from the same owner, I'll never work on their stuff again.
This is not a debatable topic. The regs are black and white. Anybody suggesting it's a matter of preference is openly advocating that you willfully break a regulation, whether you know it or not.
FYI: the regulation still is in effect for any aircraft type certified under it. Same as CAR 3 is still in effect for those aircraft certified under it. The revised Part 23 is only applicable to new aircraft certified under the current Part 23, i.e., after 2016. Regulations don't simply go away when they are revised. If they did then every aircraft certified previously would have to be upgraded to the current regulatory requirement.
write-stuff
En-Route
Sorry for the resurrection of this thread, but it still might be relevant, especially to my issue.
First, yes, I understand that pitch relative to the horizon changes based on airspeed. In fact, these pitch settings are used for various phases of instrument flight.
I recently installed several GI 275s in my 182. When the airplane is trimmed for cruise level flight, the nose shows about 5 degrees below the horizon while VSI shows 0. I can easily rationalize pitch up indications, but I'm concerned that the pitch down may suggest that I have some kind of airplane rigging problem, or the GI 275 is out of calibraion.
First, yes, I understand that pitch relative to the horizon changes based on airspeed. In fact, these pitch settings are used for various phases of instrument flight.
I recently installed several GI 275s in my 182. When the airplane is trimmed for cruise level flight, the nose shows about 5 degrees below the horizon while VSI shows 0. I can easily rationalize pitch up indications, but I'm concerned that the pitch down may suggest that I have some kind of airplane rigging problem, or the GI 275 is out of calibraion.
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Llewtrah
I think it's out of adjustment, not calibration. When I had my 275's installed, one of the actions was for me to go fly it on a VMC day and see what the attitude showed when in level flight (as demonstrated by no altitude change). I reported the results to my installer, who went into the config settings and made the adjustment. IIRC it was off by maybe 3 degrees.
You may consider documenting the offset at cruise speed and then having your installer (or other appropriately qualified person) make the change. It's not hard to change it but I'm respecting the comments above about who can and can't do it.
write-stuff
En-Route
Thanks. Yes, I have a picture showing the pitch 5 degrees below the horizon line in level flight with VSI=0. I'm also going to call Garmin before going back to the avionics shop.
Interesting, I couldn't get the nose on to the horizon with VSI=0 unless I powered down to 16 inches. At that setting/speed, I'd have expected to see a slight up indication.
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Llewtrah
Take a look in section 4 for adjusting the offset.
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Hang 4
When they are installed, the plane is supposed to be jacked to a standard "level" position from the planes service manual. Guessing yours weren't and the plane was a bit nose up on it's wheels.
