What is EHSI on Boeing 737? (Electronic Horizontal Situation Indicator)

The Electronic Horizontal Situation Indicator (EHSI) is a sophisticated navigation instrument used in the Boeing 737 aircraft to provide pilots with a clear and accurate representation of the aircraft’s position and orientation in relation to the earth’s surface. It is a crucial component of the flight deck, allowing pilots to navigate safely and efficiently.

EHSI Features and Functionality

The EHSI combines information from various sources, such as the aircraft’s GPS (Global Positioning System), Inertial Reference System (IRS), and navigation radios, to display a comprehensive view of the aircraft’s position and flight path. It presents this information on a large, high-resolution display, making it easily readable for pilots.

One of the main features of the EHSI is its ability to show the aircraft’s position graphically on a moving map display. The map shows the aircraft’s current position, flight track, and other relevant information, such as airports, navigation aids, and airspace boundaries. This allows pilots to have a clear understanding of their route and helps them navigate through complex airspace or follow specific approach procedures.

The EHSI also provides pilots with situational awareness by displaying key flight parameters, such as groundspeed, true airspeed, wind direction, and wind speed. These parameters are crucial for maintaining an optimal flight profile and fuel efficiency. Additionally, the EHSI can display weather radar information, enabling pilots to avoid hazardous weather conditions and make informed decisions about flight routing.

Another important function of the EHSI is its integration with the aircraft’s autopilot and flight management system (FMS). The EHSI can receive guidance commands from the autopilot and display them graphically, allowing the pilot to follow an accurate flight path without manual control. This feature enhances flight safety and reduces pilot workload, especially during instrument approaches and en-route navigation.

Besides these primary functions, the EHSI also provides pilots with a range of additional features and settings. Pilots can customize the display layout, choose different map orientations, and adjust the brightness and contrast of the screen. The EHSI also incorporates traffic collision avoidance system (TCAS) information, allowing pilots to be aware of nearby aircraft and take appropriate avoiding actions if necessary.

The Advantages of the EHSI

Transitioning from traditional mechanical instruments to electronic displays, such as the EHSI, has several advantages for pilots and airlines:

1. Enhanced Situational Awareness: The EHSI provides pilots with a clear and intuitive representation of the aircraft’s position, flight path, and surrounding airspace. This helps pilots maintain situational awareness and make informed decisions.

2. Reduced Workload: The automation capabilities of the EHSI, such as its integration with autopilot and FMS, reduce pilot workload by automating routine navigation tasks. This allows pilots to focus more on monitoring the flight and managing any potential anomalies.

3. Improved Safety: The accurate and up-to-date information displayed on the EHSI contributes to enhanced safety. Pilots can quickly detect and react to deviations from their planned flight profile, monitor weather conditions, and avoid potential conflicts with other aircraft.

4. Increased Efficiency: The EHSI’s integration with the aircraft’s systems and its ability to display important flight parameters enables pilots to optimize fuel consumption and reduce operating costs. It allows for more precise navigation, resulting in shorter flight times and lower fuel consumption.

5. Customizable Interface: The EHSI offers a range of customizable settings, allowing pilots to tailor the display to their preferences and optimize their workflow. Pilots can adjust the map orientation, display layout, and brightness to maximize their efficiency and comfort.


The Electronic Horizontal Situation Indicator (EHSI) is a critical component of the Boeing 737 aircraft’s navigation system. It combines data from multiple sources to provide pilots with a clear and detailed understanding of the aircraft’s position, flight path, and surrounding environment. The EHSI’s advanced features, such as graphical map display, integration with automation systems, and customizable settings, enhance pilot situational awareness, reduce workload, improve safety, and increase operational efficiency.

The integration of electronic displays like the EHSI represents a significant advancement in aviation technology, revolutionizing the way pilots navigate and enhancing overall flight operations. As technology continues to evolve, it is expected that future iterations of the EHSI will offer even more advanced features and capabilities, further improving flight safety and efficiency.

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