Flight Redemptions

What is CDI in Aviation? (Course Deviation Indicator)

Updated: February 20, 2024

What is a Course Deviation Indicator (CDI)?

A Course Deviation Indicator (CDI) is a crucial instrument used in aviation to provide pilots with accurate information on their current position relative to their desired course. It is a part of the cockpit's navigation system, often integrated with other instruments such as the Horizontal Situation Indicator (HSI) or the Radio Magnetic Indicator (RMI).

The CDI visually represents the aircraft's position in relation to the selected course by using a needle and a scale. The needle moves left or right, indicating how far off the desired course the aircraft is. The scale provides numerical values, allowing pilots to determine the exact deviation in nautical miles. The CDI also includes a vertical bar or flags to indicate when the aircraft is centered on the course or deviating.

How Does a Course Deviation Indicator Work?

The CDI operates based on signals received from the aircraft's navigation system, typically from a VHF Omni-directional Range (VOR) or a Global Positioning System (GPS). These signals are used to calculate the course deviation and display it on the instrument.

When the aircraft is on the desired course, the CDI needle remains centered, indicating that the aircraft is on track. However, if the aircraft deviates to the left or right, the needle will move accordingly. The amount of movement corresponds to the magnitude of the deviation. Pilots can then make adjustments to steer the aircraft back onto the desired course.

The CDI's scale provides additional information. It shows the distance in nautical miles between the aircraft's current position and the desired course. Pilots can use this information to understand the magnitude of the deviation and make appropriate corrections.

In more advanced aircraft, the CDI may also incorporate other features such as a glideslope indicator for precision approach during landing or a wind correction indicator to account for crosswinds.

Importance of the Course Deviation Indicator in Aviation

The Course Deviation Indicator is a vital tool for pilots, especially during instrument flight and navigation in challenging weather conditions or unfamiliar airspace. Here are a few reasons why the CDI is crucial:

Accurate Positioning: The CDI enables pilots to accurately determine their position relative to the desired course, helping them navigate along the intended path.
Course Correction: By providing real-time feedback on deviations, the CDI allows pilots to make timely adjustments to bring the aircraft back on track.
Situational Awareness: The CDI's visual representation of the aircraft's position enhances situational awareness, helping pilots maintain a clear understanding of their surroundings and potential obstacles.
Navigation Aid: In instrument flight, the CDI assists pilots in following instrument approaches, airway routes, and other designated flight paths.
Backup Navigation: In the event of a failure of other navigation systems, the CDI can serve as a reliable backup for pilots to maintain course integrity.

The Course Deviation Indicator plays a critical role in enhancing safety and precision in aviation. It assists pilots in maintaining accurate navigation and contributes to the overall effectiveness of the flight management system.


The Course Deviation Indicator (CDI) is an essential instrument in aviation that provides pilots with real-time information on their aircraft's position relative to the desired course. By visually representing the deviation and providing numerical values, the CDI enables pilots to make accurate course corrections and maintain situational awareness. Its importance in navigation, instrument flight, and safety cannot be overstated. Pilots rely on the CDI to ensure precise and efficient flight operations, particularly in challenging conditions. Understanding the functionality and significance of the CDI is crucial for pilots and aviation enthusiasts alike.

Recent Posts