How’s your attitude? No, we’re not talking about your pilot mindset, though that is important too, and we do have some fun “punny” men’s and women’s bad attitude tees that embrace this classic play-on-words bit of pilot humor.
No, today we are continuing our aircraft instrumentation series with a deep dive on the attitude indicator, or “AI” for short. During flight, VFR pilots can simply look outside the cockpit at the wings and the aircraft’s cowling’s relationship to the horizon, then use that visual as their unofficial “attitude indicator.” For IFR pilots flying on instruments, however, the AI is critically important.
But don’t tune out yet, VFR pilots. Knowledge is valuable. Plus, there is always a chance you could one day fly into rapidly developing instrument meteorological conditions (IMC). In that circumstance, you would need to know the basics of how to use your instruments to maintain control of the aircraft and fly back to clear weather.
Instrument flying experience is also important at night when night flying illusions can easily cause disorientation. Flying at dusk and dawn can also play havoc on your eyes. Many times, the horizon is not even visible. It’s just a solid haze between the sky and the ground. If you’re comfortable using your instruments, you’ll be able to cross-check what you think you see or feel.
Ready to learn more about one of the important instruments that all pilots both VFR and IFR should understand?
Keep reading for a refresher on what the AI gauge is, how it works, how to read it, and potential instrument errors to watch out for.
What is an attitude indicator?
The AI is a direct indicator gyroscopic flight instrument mounted in the cockpit of aircraft. It displays both pitch and bank against an artificial horizon display.
There are several types of AIs including the traditional attitude indicator (which we will be talking about in this post), an electric attitude indicator, digital attitude indicator, and all-in-one attitude indicator. (To learn more about the other types of indicators, refer to Lambda Geeks’ attitude indicator article.)
What does an attitude indicator do?
Also referred to as an artificial horizon or gyro horizon, the AI monitors your aircraft’s orientation relative to the Earth’s horizon. This instrument is built to measure both pitch and bank/roll. When used along with the heading indicator and turn indicator, the attitude indicator helps pilots maintain straight and level flight as well as execute coordinated turns, maintaining bank control throughout.
How does the attitude indicator give its reading?
Attitude indicators are also called gyro horizons or attitude gyros because they use a built-in gyroscope as the source of their readings. The AI’s gyroscope is usually powered using suction from an onboard vacuum pump, although in some planes it can operate on direct current from the electrical system instead.
The AI gyro is gimbled with a vertical spin axis. The indicator’s gimbal rings freely spin on the lateral and longitudinal axes so the instrument can give both pitch attitude and roll attitude data. As a direct indictor instrument, the AI shows bank and pitch attitude changes in real time with no lag.
Note: In a glass cockpit, instead of a physical gyroscope, a solid-state attitude indicator gets its data from the Attitude Heading Reference System (AHRS), Inertial Reference Unit (IRU), and the Inertial Navigation System (INS).
How to read an attitude indicator
Now that we know what information the AI provides and how it works, how do we read and use our AIs? The AI gives you a quick snapshot of both your pitch and bank attitudes in a single glance. Its gauge contains a pictorial representation of an aircraft, the sky, the land, and an artificial horizon line.
As you dip your wings into a banking turn, or bring your aircraft’s nose up/down, the position of the miniature aircraft on the gauge face will mirror your actions. Hash marks, pointers, arrows, and lines on the face help quantify the degree of change.
After reading the rest of this article, watch Aviation Theory’s attitude indicator video to see examples of the different attitude indicator designs. You’ll also get tips on how to read sky pointers (the sometimes-confusing glass cockpit versions of analog attitude indicators) and see an easy-to-follow visual of how gyroscopic precession works.
How to read a bank indicator
The little aircraft icon is good for a quick visual check of your bank. Your bank indicator shows your bank angle, or the angle between the horizon and your plane’s lateral axis.
As you enter a bank, the miniature aircraft on your attitude indicator gauge will roll left or right with you. For more precise bank degree readings, look at the curved banking degree scale along the top of the gauge face. Also check the position of the bank indicator pointer in relation to the fixed banking scale hash marks.
Most gauges have large hashes for 30- and 60-degree bank angles along with a dot-shaped indicator for 45-degree banks. Thinner hash marks for 10-, 20-degrees serve as visual interpolation aids for other bank angles under 30-degrees.
Pro Tip: Don’t confuse the turn coordinator with the bank indicator. Your turn coordinator indicates if and at what speed your aircraft is turning. The bank indicator simply measures the angle between your wings and the horizon.
How to read a pitch indicator
The pitch indicator portion of your attitude AI measures the angle between the horizon and the longitudinal axis of your aircraft. In simple terms, it measures how much your aircraft’s nose is angling up or down relative to the horizon.
As the gyroscope of your attitude indicator registers a change in pitch, the miniature aircraft on your gauge will move vertically up or down relative to the artificial horizon. Watch for the position of the little dot between the wings of the mini plane. This marks your current pitch angle. Pitch angles are communicated using horizontal lines in 5-degree increments both up and down. The 5-degree lines are short and alternate with long 10-degree increment labeled lines.
Pro Tip: The pitch indicator doesn’t tell you if your plane is climbing or descending. It only communicates the attitude. You’ll need to check your vertical speed indicator (VSI) to know if your altitude is changing and if so, how quickly.
Common attitude indicator errors
The good news is that AIs have rather limited errors, most of which can be easily corrected.
Attitude Adjustment Knob Misalignment
Some attitude indicators have an adjustment knob that lets you move the miniature aircraft based on your point of view. Be sure you only make such adjustments when you are on the ground or at least flying straight and level in visual meteorological conditions (VMC).
Pitch and Bank Limits Exceeded
Older AIs had pitch limits of 60-degrees and bank limits of 100-degrees. Exceeding those limits would cause the gyro to “topple” and need to realign with the horizon. The good news is that newer AIs usually have pitch limits of at least 85-degrees and no bank limits at all.
Since the Earth rotates at about 15-degrees per hour, the attitude indicator’s gyro alignment drifts away from the actual horizon over time. For vertical gyros like the attitude indicator, the drift effect is worst at the equator and less severe at the North and South Poles. To offset precession, your indicator should periodically re-align with the horizon. If you notice it has drifted off and not realigned, you can manually align when at a straight and level attitude or on the ground.
In a vacuum-powered gyro system, if the instrument’s container box fails, contaminants can seep in, and air can leak out. Both cause reading errors.