What is NG in Aviation? (Gas Generator Speed)

Gas generator speed, abbreviated as Ng, is a crucial concept in the field of aviation. It refers to the rotational speed of the gas generator, which is a key component of a gas turbine engine. The gas generator consists of a compressor and a turbine, which work together to produce the necessary power for the aircraft’s propulsion system.

In this article, we will dive into the details of gas generator speed, its importance in aviation, and its impact on the overall performance of an aircraft. Let’s explore the world of gas generator speed and unravel its significance in the realm of aviation.

The Significance of Gas Generator Speed

The gas generator speed plays a critical role in determining the performance and efficiency of a gas turbine engine. It is directly related to the production of power and the overall thrust generated by the engine. By controlling the gas generator speed, pilots and engineers can optimize the engine’s operation and ensure optimal performance during different flight phases.

Gas generator speed is typically measured in percentage, with 100% representing the maximum recommended speed for a specific engine. Operating the gas generator speed within the recommended range is essential for maintaining the engine’s health and preventing potential damage.

Gas Generator Speed and Engine Efficiency

One of the critical aspects influenced by gas generator speed is the engine’s efficiency. The efficiency of an engine refers to its ability to convert fuel into useful work, which is measured in terms of thrust or power output. The gas generator speed directly affects the engine’s efficiency by influencing the airflow and combustion process within the engine.

When the gas generator speed is too low, it can lead to inadequate airflow and inefficient combustion. This results in reduced power output and a decrease in overall engine performance. On the other hand, operating the engine at a high gas generator speed can also have negative consequences.

At high gas generator speeds, the engine may experience excessive wear and tear due to increased stress on various components. It can also lead to higher fuel consumption and increased emissions. Therefore, finding the optimum gas generator speed that balances efficiency and engine health is crucial in aviation.

The Role of Gas Generator Speed in Flight Phases

The gas generator speed needs to be carefully monitored and controlled throughout various flight phases. Let’s explore its role in different stages of flight:

Takeoff and Climb

During takeoff and climb, the aircraft requires maximum thrust and power to overcome the force of gravity and gain altitude. The gas generator speed plays a crucial role in providing the necessary power to achieve these objectives. Pilots will typically set the gas generator speed at its highest recommended level to ensure maximum thrust output.

However, it is important to monitor the engine parameters and avoid exceeding the maximum gas generator speed limit, as it can lead to engine damage. The aircraft’s climb performance and acceleration are directly affected by the gas generator speed, making it a critical factor during this phase of flight.


Once the aircraft reaches its cruising altitude, the gas generator speed is adjusted to a more optimal level for continuous flight. This level is typically lower than the maximum speed used during takeoff and climb. Operational considerations, fuel efficiency, and engine longevity are taken into account when determining the gas generator speed for cruise.

Choosing the right gas generator speed during cruise allows for an efficient and smooth operation of the engine. It helps in reducing fuel consumption and maximizing the aircraft’s range, which is particularly important during long-haul flights. Maintaining a stable gas generator speed throughout the cruise phase ensures a comfortable and economical journey for passengers.

Approach and Landing

During the approach and landing phase, the gas generator speed is adjusted once again to meet the specific requirements of descending and preparing for touchdown. A lower gas generator speed is often used to reduce the engine’s power output and provide better control during the landing process.

This adjustment in gas generator speed allows the aircraft to descend smoothly and maintain the desired approach speed. It also aids in minimizing the noise and environmental impact during the landing phase. Pilots carefully manage the gas generator speed to ensure a safe and controlled landing of the aircraft.


Gas generator speed, abbreviated as Ng, plays a vital role in the aviation industry. It impacts engine efficiency, power output, and overall aircraft performance. By understanding the significance of gas generator speed and its role in different flight phases, pilots and engineers can ensure safe and efficient operations.

Optimizing gas generator speed helps in achieving the desired thrust, reducing fuel consumption, and maximizing engine longevity. It requires careful monitoring and adjustment during takeoff, climb, cruise, approach, and landing. By maintaining the right gas generator speed, aviation professionals can enhance the performance and reliability of gas turbine engines.

For more information on gas generator speed and its impact on aviation, check out this article from Aviation Maintenance School.

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