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As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics. (Probably related: this question)

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.

As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics. (Probably related: this question)

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.

Perhaps as a side-note regarding this set of equations: These are flat earth approximations (not related to the conspiracy theory :D). Therefore not really suited for navigation purposes if you want to navigate further then lets say 30-50km. After this distance, the error accumulates and gives distance errors in the 10s of meters. In applications like short term path planing like landing planing or short-term path following, these are fine however.

As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics.

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.

As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics. (Probably related: this question)

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.

As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics.

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.

As you noticed, you do not need this information for navigation per se, and you are right. If you can measure the rotational rates $p$, $q$ and $r$ directly, then you do not need to worry about updating the rotational rates.

However there are a couple of reasons why you might be interested in this equation anyways.

1. This completes the set of equations. These are generally called the equations of motions of an aircraft and are central for flight dynamics. Therefore this set of equations describes how an aircraft moves/rotates/behaves in the air.

2. For real-world navigation you also might use this formula for example inside a data-fusion scheme. No sensor is perfect, therefore directly using the rotational rates for your navigation solution might lead to undesirable results. For this reason, often data fusion approaches like a Kalman Filter are used which fuse sensor data and model data. For the model data part of this filter you need a mathematical model, which is exactly posed by the rotational dynamics.

3. Last but not least, these equations are used for simulation purposes. If you want to numerically simulate an aircraft for whatever purpose, you absolutely need these equations. Simulations are of course central for a whole myrade of applications such as flight simulators (e.g for testing your navigation filter), general flight dynamics analysis, controller synthesis, and so on.

From the context you provide, I would speculate that the author wanted to give the complete set of equations.