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I used to fly a Cessna 550 with 'steam gage' mechanical gyros. The Attitude Indicator always had its flight director solidly on the horizon in level flight -- to the extent a mechanical instrument could be seen accurately.

I recently started flying a Phenom 300 with a G1000 panel. It is curious to me that level flight in the Phenom is always about 2.0º nose up pitch:

enter image description here

And a detailed pic of the command bars in level flight at FL430:

enter image description here

My question: Why would level flight be indicated by nose up pitch? What does 'level' actually refer to?

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    $\begingroup$ BARO minimums 10,640? Impressive ;) $\endgroup$
    – TypeIA
    Jul 30, 2020 at 5:53
  • $\begingroup$ You are assuming this is due to a difference between the avionics suites, where in reality the difference can be due to aircraft design $\endgroup$
    – DeepSpace
    Jul 30, 2020 at 10:47
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    $\begingroup$ This annoys me too. I have only flown this kind of stuff once or twice, but I don't need the attitude indicator to remind me that some positive AoA is required for lift. Instead, when I am in instrument conditions I want to set the pitch bug for my zero VSI attitude. $\endgroup$
    – Michael Hall
    Jul 30, 2020 at 14:54
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    $\begingroup$ BARO minimums 10,640? Set up for the KTEX RNAV (GPS) Z RWY 9 have a look $\endgroup$
    – dawg
    Jul 30, 2020 at 15:23

4 Answers 4

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Level flight just means not climbing or descending. Where the nose is actually pointing is another matter.

The pitch you are seeing is the "deck angle". Pitch attitude is normally referenced to the longitudinal axis of the fuselage (and normally, the cabin floor or deck) relative to the horizon for the loading and speed you are at.

The deck angle will be the overall AOA of the wing for a given flight condition plus or minus the wing incidence relative to the fuselage. If the incidence is zero, meaning the wing mean chord line is parallel to the fuselage's long axis, and the wing is operating at a 2 degree overall AOA at that altitude and speed, there's your pitch attitude; +2. I would expect to see at least a deck angle of a couple degrees when flying at 210 kt indicated in a jet, unless the wing had an incidence of several degrees.

Say the Phenom has a wing incidence of about 1 degree, and that the wing is actually working at an overall AOA of 3 degrees at 210kt; the resulting deck angle would also be +2.

In the Citation with the mechanical spherical attitude indicator with Flight Director, you have to allow for the parallax error due to the gap between the indicator and sphere if your sight line is off a bit, and perhaps the Citation II has a higher wing incidence, and along with a lower wing loading cruises with a lower deck angle of 1 degree or less. With a mechanical indicator it'd probably look close enough to 0 degrees to make that conclusion.

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I was always told that an analog AI should be set to the white horizon line while on level ground, rather than for straight and level flight. The reason for this is that it offers a truer picture of the pitch of the nose above the imaginary horizontal plane.

For example, a Cessna 172 in straight and level flight will actually be in an orientation with the nose about 2.5 degrees above horizontal. It’s entirely likely that the Phenom balances S&L with a slightly nose-up pitch as well. Unfortunately, the G1000 does not offer the ability to calibrate this for yourself according to preference.

Perhaps, take solace in the fact that you now have a somewhat more accurate reading of the actual pitch of the aircraft during its various maneuvers and configurations.

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  • $\begingroup$ The adjustment on analog gauges is only for parallax, which isn’t an issue with glass. $\endgroup$
    – StephenS
    Jul 30, 2020 at 13:03
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    $\begingroup$ @StephenS the adjustment is intended to correct for parallax, which is exactly what is does if you adjust it on the ground during run-up. But someone could use it to correct for typical flight attitude and now be disappointed that it isn't available on the glass instrument (which has no parallax to correct for). $\endgroup$
    – Jan Hudec
    Jun 24, 2021 at 13:25
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At FL430 cruise, your aircraft is probably exhibiting a real nose-up pitch attitude in order to achieve the wing's best-economy AoA at that point in the flight envelope and the electronic detectors in the pitch attitude indication system are showing you this.

Taking a vacuum-driven "steam gauge" gyro apart reveals a set of clever doodads called erector mechanisms inside it which are intended to determine the average direction of "up" on long-term (~tens of minutes) timescales. It is possible, then, that the steam gauge system was nulling out the persistent (but slight) steady-state nose-up pitch condition in high altitude cruise.

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    $\begingroup$ near-stall regime of its flight envelope -- Phenom's are not like Lear's; At FL43 or FL45 at normal cruise they are 10 to 15 kts from the barber pole redline (as you can see in the picture) and 50kts above stall speed (which is dynamically calculated, displayed on the speed tape, and not seen in the pic) Throttled back to LRC, we could be cruising at 160 - 170kts indicated and still be 30 kts above stall. $\endgroup$
    – dawg
    Jul 30, 2020 at 15:28
  • $\begingroup$ thanks @dawg, will edit. -NN $\endgroup$
    – niels nielsen
    Jul 30, 2020 at 16:04
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    $\begingroup$ The erector can nullify slight turn because in a coordinated turn the apparent gravity is still towards the floor. But in an unaccelerated straight and level flight the only inertial force is due to gravity (because there is no acceleration), so it can't null out the steady state pitch that way. $\endgroup$
    – Jan Hudec
    Jun 24, 2021 at 13:05
  • $\begingroup$ @JanHudec -- I just noticed that error too, before reading your comment. Funny how that was allowed to stand uncorrected for well over a year. Likewise flying along in wing-low straight-line slip also wouldn't cause any automatic "correction" of the gyro to make it read incorrectly. $\endgroup$
    – quiet flyer
    Jun 25, 2021 at 13:27
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In level flight, it's natural to have some nose-up pitch. You need some angle of attack to produce lift that counteracts gravity. "Level" on the attitude indicator probably refers to 0 angle of attack, or how the plane sits when it's on the ground wheels down and the G1000 is being calibrated.

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  • $\begingroup$ However, there could be positive angle of attack or, indeed positive wing pitch attitude, of the wing and zero pitch attitude of the airplane (be it the rotor axis or the thrust axis or the seating surface level or whatever. $\endgroup$
    – Vladimir F Героям слава
    Jul 30, 2020 at 13:54

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