What is EET in Aviation? (Estimated Elapsed Time)

Estimated Elapsed Time (EET) is a crucial concept in aviation. It refers to the amount of time it takes for an aircraft to travel from one point to another, taking into account factors such as distance, speed, and wind conditions. EET is used by pilots and air traffic controllers to plan flights, estimate fuel requirements, and ensure the safety and efficiency of air travel.

When calculating the EET for a flight, several factors come into play. Firstly, the distance between the departure and destination points is considered. This can be determined by measuring the great circle distance, which is the shortest path between two points on the surface of a sphere (in this case, the Earth).

Secondly, the true airspeed of the aircraft is taken into account. True airspeed refers to the speed of an aircraft relative to the air mass in which it is flying, without taking into account any external factors such as wind. It is typically measured in knots (nautical miles per hour).

Lastly, wind conditions play a significant role in calculating the EET. Both headwinds and tailwinds can affect the speed of an aircraft. A headwind is wind blowing directly against the direction of travel, while a tailwind is wind blowing in the same direction as the aircraft’s motion. Headwinds can decrease the groundspeed of the aircraft, while tailwinds can increase it.

The formula used to calculate EET takes into consideration the true airspeed, distance, and wind conditions. It can be expressed as:

EET = Distance / True Airspeed +/- Wind Correction

How is Estimated Elapsed Time Used in Aviation?

EET is essential for flight planning and coordination. It allows pilots to estimate the duration of a flight and ensures that they have enough fuel on board to reach their destination safely. Additionally, air traffic controllers use EET to manage the flow of air traffic and optimize airspace utilization.

One of the primary uses of EET is in flight planning. Pilots need to know how long a flight will take to determine fuel requirements and make any necessary arrangements for passenger comfort and safety. By calculating the EET, pilots can also plan their navigation and communicate their estimated time of arrival (ETA) to air traffic control and ground personnel.

EET is also crucial for air traffic controllers. By knowing the estimated elapsed time for each flight, controllers can effectively manage the flow of air traffic, especially during busy periods. They can coordinate takeoff and landing slots, calculate separation between aircraft, and allocate airspace resources in an efficient manner. EET helps prevent congestion and ensures the safe and smooth operation of air traffic.

Factors Affecting Estimated Elapsed Time

Several factors can affect the estimated elapsed time of a flight. These include:

1. Wind Conditions: As mentioned earlier, headwinds and tailwinds can significantly impact the speed of an aircraft. A strong headwind can increase the flight time, while a tailwind can reduce it. Pilots and air traffic controllers must consider the current wind conditions along the planned route and make adjustments accordingly.

2. Aircraft Performance: The performance capabilities of the aircraft also play a role in determining the EET. Different aircraft have different cruising speeds, fuel efficiencies, and altitude capabilities. These factors can influence the estimated elapsed time for a particular flight.

3. Air Traffic Control Instructions: Air traffic control instructions, such as route changes or altitude restrictions, can affect the estimated elapsed time. Pilots must adhere to these instructions while considering their impact on the flight duration.

4. Airspace Restrictions: Certain airspace regions may have restrictions that require aircraft to divert from their intended path. These diversions can add to the estimated elapsed time. Pilots and air traffic controllers must plan accordingly and consider alternative routes to avoid delays.

5. Weather Conditions: Weather conditions such as storms, thunderstorms, or icing can also impact the estimated elapsed time. Pilots may need to alter their flight plans or make detours to avoid dangerous weather, which can result in deviations from the initially calculated EET.


Estimated Elapsed Time (EET) is a crucial aspect of aviation planning and coordination. It helps pilots estimate the duration of a flight, plan fuel requirements, and communicate estimated arrival times. Air traffic controllers use EET to manage traffic flow and optimize airspace utilization. Understanding the factors that affect EET, such as wind conditions, aircraft performance, air traffic control instructions, airspace restrictions, and weather conditions, is essential for accurate flight planning. By considering these factors and calculating the estimated elapsed time, aviation professionals can ensure safe and efficient travel in the skies.

For More: What is DLR in Aviation? (Datalink Recorder)