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What You Should Know About Angle-Of-Attack Indicators

Swayne Martin

Have you ever flown an airplane with an AOA indicator? They're becoming more common in GA airplanes, and they're a great safety tool. Here's what you should know...

What's The Point?

Angle-of-attack (AOA) indicators provide a visual representation of how much lift is being generated by your wings for a given airspeed. This is incredibly useful because speed alone is not a reliable parameter to avoid a stall. That's because airplanes can stall at any speed, as long as they exceed their critical angle-of-attack.

You should think of AOA indicators as instruments for stall margin awareness. In short, AOA indicators measure the current AOA of the aircraft in comparison to the aircraft's critical AOA. Let's dig a little deeper...

Garmin

The Critical AOA

For a given configuration, an airplane will always stall at the same AOA, called the critical angle-of-attack. The critical AOA does NOT change with:

  • Weight
  • Bank Angle
  • Temperature
  • Density Altitude
  • Center of Gravity

Let's say you're flying a steep turn. How do you turn and maintain altitude at the same time? You need to increase the total amount of lift your wing is producing. And to do that, you need to pull back on the yoke, which increases the angle-of-attack that your wing is flying at. This part is important, because when you increase your angle-of-attack, you get closer to the critical angle-of-attack, which is the point when your wing stalls (regardless of airspeed or attitude).

Without an AOA indicator, the AOA is "invisible" to pilots. In certain configurations and attitudes, you might not realize you're approaching a stall.

How It Works

We won't dive into the specific system components or measurements used to calculate AOA, because each variant system has its own parameters. In corporate, airline, and military flying, you'll often see "vane style" AOA indicators. They show direct indications of AOA, but must be mounted in a position with clean airflow.

Wikimedia

In general aviation, you'll commonly see "pressure-derived" AOA indicators. Most of these measure pressure differences at the pitot tube to determine an accurate AOA. While extremely popular and affordable, most of these models don't calculate AOA based on various flap configurations. However, they're still a very useful tool.

Dynon Avionics

However, some of the newest glass-cockpit systems provide AOA data including flap configuration changes. Reference your aircraft's POH for more information.

https://buy.garmin.com/en-US/US/p/682215/pn/G3X-TCERT-01#

The FAA Is Concerned, And Made Installation Easy

In 2014, the FAA released major changes to expand the installation of AOA indicators in general aviation aircraft. Under these new policies, an appropriately rated mechanic can install an AOA indicator by a field approval or a minor alteration in the aircraft maintenance logs. Here's what the FAA has to say...

Preventing loss of control in general aviation (GA) is a top focus area of the FAA and the GA community. Installation of an AoA system may aid in preventing loss of control accidents. Manufacturers have requested a streamlined method of design and production approval for nonrequired/supplemental systems. Since these systems provide only supplemental information to the pilot and are not required by regulation, the FAA has developed the following approval process under 14 CFR 21.8(d).

Want Another Visual Representation?

Check out this video made by Sam Sheperd. This video is a great resource for showing flight students visual representations of how AOA changes across various flight parameters. Fast forward to 1:50 in the video for takeoff...

Have You Used An AOA Indicator?

Tell us about your experiences flying with an AOA indicator. What did you find useful? Was there anything you didn't like? Share in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

Images Courtesy:

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