Attitude & Heading Reference System (How It Works)

Understanding how the different systems in your aircraft work is essential to being a good pilot. Learn about the AHRS system and how it works in this guide.

I know, I know. Yet another aircraft system that you have to understand. Does it ever end? It’s true, there are all kinds of parts, pieces, and systems that you have to know about to be a good pilot. But the more you know, the better you’ll understand how your plane is flying, and the better pilot you’ll be. So what exactly is the attitude and heading reference system?

The attitude & heading reference system is part of an aircraft’s navigational system that helps the pilot know how the aircraft is flying and in what direction. The system is generally made up of an accelerometer, a magnetometer, and a gyroscope that work together and relay info to the pilot.

An airplane's attitude and heading reference system, or AHRS, is a key part of the aircraft's navigation system. In this article, we will discuss how these parts work together to create an accurate picture of the airplane's position and movement. We will also talk about some of the potential problems with the AHRS system, such as magnetic disturbances and gyro drift.

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‍What is an Attitude & Heading Reference System?

Before we can get into how an attitude & heading reference system (AHRS) works, we need to give you an idea of what it even is in the first place. We'll of course get into the much deeper details about it all once we start looking at the various parts and pieces that make up the system and how they work together, so for now let's look at a high-level overview of what it is.

In a nutshell, the AHRS on an aircraft is responsible for providing the pilot with information about the attitude and heading of the aircraft. That much was pretty self-explanatory, right? You probably could have guessed that just from the name of the system itself. Basically, this system is part of the aircraft's advanced navigation system that relays information to the pilot about how the plane is currently flying.

To understand it a bit more, let's look at what attitude and heading are in the first place.

What is Attitude While Flying?

Attitude simply refers to the orientation of the aircraft in relation to the earth. This includes things like pitch, roll, and yaw. Let's briefly go over each of these three factors so that you have a better understanding of what they are and how they affect the plane.

• Pitch: This is how far the nose of the plane is pointing up or down in relation to the horizon.
• Roll: This is how far the plane has tilted from one side to the other. When a plane is rolled, it means that one wing is lower than the other.
• Yaw: This is how far the nose of the aircraft has turned left or right in relation to the direction it is currently flying.

All of these factors are important for the pilot to know so that they can maintain control of the aircraft. The AHRS system on board the aircraft is responsible for measuring all of these factors and relaying them back to the pilot in real-time.

What is Heading While Flying?

Heading, on the other hand, refers to the direction that the aircraft is currently flying in. This is measured in degrees from the north and can be anywhere between 0 and 360. The heading of an aircraft is important for the pilot to know so that they can make course corrections as needed and ensure that they are flying in the right direction.

Now that we have a basic understanding of what attitude and heading are, let's take a look at the various parts that make up the AHRS and how they work together.

Parts of an Attitude & Heading Reference System

While there is a bit more nuance to it than this, the attitude & heading reference system is made up of three main parts: an accelerometer, a magnetometer, and a gyroscope. Let's look at what each of these three parts are before we talk about how the system actually works.

AHRS Accelerometer

The accelerometer is responsible for measuring the acceleration of the aircraft. This includes things like gravity and centrifugal force. The accelerometer is what tells the system how fast the aircraft is changing directions and helps to keep track of its orientation in relation to the earth.

AHRS Magnetometer

The magnetometer, on the other hand, is responsible for measuring the magnetic field around the aircraft. This information is then used to calculate the heading of the aircraft. The magnetometer is what tells the system which way is north so that it can properly orient the aircraft.

AHRS Gyroscope

Finally, we have the gyroscope. The gyroscope is responsible for measuring the angular velocity of the aircraft. This information is then used to calculate the rate of change for the pitch, roll, and yaw. The gyroscope is what tells the system how fast the aircraft is changing its orientation and helps to keep track of its attitude.

How Does an Attitude & Heading Reference System Work?

Now that we know a bit more about the various parts that make up an AHRS, let's talk about how they all work together.

As we mentioned before, the system is responsible for measuring the attitude and heading of the aircraft. It does this by constantly taking readings from the accelerometer, magnetometer, and gyroscope. These readings are then used to calculate the attitude and heading of the aircraft in real-time.

Once the pilot knows the attitude and heading of the aircraft, they can then make the necessary adjustments to keep it flying in the right direction. For advanced aircraft such as commercial airplanes, the autopilot system also uses the information from the AHRS to help keep the aircraft on course.

Potential Issue with an Attitude & Heading Reference System

While the AHRS is a very accurate system, there are potential issues that can arise. After all, just about any system on any aircraft has potential issues that can pop up from time to time. The important thing is to know what the issues are so that you have an idea about how you can mitigate them and compensate when they do arise.

Magnetic Disturbances Can Affect the Magnetometer

One potential issue that can affect the AHRS is magnetic disturbances. These disturbances can come from things like lightning or power lines. When these disturbances occur, they can cause the magnetometer to give inaccurate readings. This, in turn, can lead to the system giving incorrect information about the heading of the aircraft.

Prolonged Acceleration Can Affect the Accelerometer

Another potential issue that can affect the AHRS is prolonged acceleration. This can happen when the aircraft is taking off or landing. When the aircraft is accelerating for a prolonged period of time, it can cause the accelerometer to give inaccurate readings. This is because the accelerometer is sensitive to changes in velocity.

If the aircraft is accelerating for a long period of time, the accelerometer will show that the aircraft is constantly changing velocity, even when it is not. This can cause the AHRS to give inaccurate readings and can potentially lead to problems.

Gyro Drift Can Lead to Bad Data From the AHRS

One potential issue with the AHRS is gyro drift. Gyro drift is when the gyroscopes in the system don't provide accurate data due to their own movement. This can be caused by a number of factors, including vibration, temperature changes, and electromagnetic interference. When this happens, it can lead to bad data from the system, which can then cause problems for the airplane.

There are a few ways to combat gyro drift. One is to use multiple gyroscopes in the system so that if one is off, the others can still provide accurate data. Another is to use a gyro with a lower drift rate. And finally, you can regularly calibrate the system to account for any drift that has occurred.

Despite these potential issues, the AHRS is still a vital part of an airplane. It provides pilots with the information they need to fly the plane safely and effectively. And with advances in technology, the system is only getting better and more reliable. So if you're ever up in an airplane, rest assured that the AHRS is working hard to keep you safe and on course.