What is TRA on Boeing 737? (Thrust Resolver Angle)

The Thrust Resolver Angle (TRA) plays a crucial role in the operation of the Boeing 737 aircraft. It is a parameter that directly affects the performance and efficiency of the plane’s engines. In this article, we will explore what the TRA is, its significance in the context of the Boeing 737, and how it is controlled and adjusted for optimal aircraft performance.

Understanding Thrust Resolver Angle

The Thrust Resolver Angle (TRA) is the angle at which the aircraft’s engine is mounted relative to the wing’s chord line. It determines the direction and magnitude of the thrust produced by the engines. The TRA affects the aircraft’s stability and control during different flight conditions.

On the Boeing 737, the engines are mounted under the wings. The TRA is designed to optimize the engine’s performance by aligning the thrust with the aircraft’s centerline and minimizing any undesirable effects caused by engine asymmetry. In simple terms, it ensures that the engine’s thrust is directed straight ahead when the aircraft is in level flight.

Controlling the Thrust Resolver Angle

The TRA on the Boeing 737 is not a fixed parameter and can be adjusted to suit different flight conditions. The primary control mechanism for the TRA is the Thrust Lever Angle (TLA). Pilots use the thrust levers in the cockpit to control the TRA and thus, the engine thrust.

When the thrust levers are set to the takeoff position, the TRA is typically set to a higher angle, directing the engine’s thrust slightly downward to counteract the aircraft’s natural nose-up tendency during takeoff. This helps to maintain a positive pitch attitude and ensures proper climb performance.

During cruise, the thrust levers are usually set to the climb/cruise position. At this setting, the TRA is adjusted to achieve level flight and optimal performance. The thrust is directed straight ahead, ensuring efficient engine operation and minimal drag. It is important to note that the TRA adjustments are made automatically by the engine’s control system based on the thrust lever position selected by the pilot.

The Significance of Thrust Resolver Angle

The Thrust Resolver Angle has several significant effects on the performance and handling characteristics of the Boeing 737.

1. Stability and Control: The TRA contributes to the aircraft’s stability and control by ensuring that the engine’s thrust is aligned with the centerline of the aircraft, reducing the potential for asymmetric thrust effects. This improves the aircraft’s handling and reduces the workload for the pilots.

2. Takeoff Performance: During takeoff, the TRA adjustment helps to maintain a positive pitch attitude and ensures that the aircraft reaches the desired climb rate. By directing the thrust slightly downward, the TRA counteracts the aircraft’s natural tendency to pitch up, enabling a smooth and controlled takeoff.

3. Fuel Efficiency: The TRA plays a role in optimizing the engine’s performance and fuel efficiency. By having the thrust directed straight ahead during level flight, the aircraft experiences minimal drag. This allows the engines to operate at their most efficient thrust setting, resulting in reduced fuel consumption.

It is important to note that the TRA adjustments are not solely responsible for these effects. The overall aerodynamic design, flight control system, and engine characteristics also influence the aircraft’s performance. However, the TRA remains a critical parameter that helps achieve the desired handling and operational efficiency of the Boeing 737.

The Future of Thrust Resolver Angle

As technology continues to advance, aircraft manufacturers are constantly looking for ways to improve performance, efficiency, and safety. The concept of variable geometry engines, also known as adaptive engines, is one area of research that has the potential to impact the TRA in the future.

Variable geometry engines have the capability to change their inlet and exhaust geometries to optimize performance at different flight conditions. By adjusting these parameters, it may be possible to modify the TRA dynamically during flight to further enhance the aircraft’s performance and reduce fuel consumption.

While variable geometry engines are not yet in widespread use, ongoing research and development in this field could pave the way for advancements in engine technology. As a result, the Thrust Resolver Angle may evolve alongside these developments to leverage the full potential of future aircraft engines.


The Thrust Resolver Angle (TRA) is a critical parameter in the operation of the Boeing 737. It determines the direction and magnitude of engine thrust, contributing to stability, control, takeoff performance, and fuel efficiency. Pilots can adjust the TRA using the thrust levers in the cockpit, allowing for optimized performance in different flight conditions.

While the TRA remains an essential component of current aircraft design, ongoing research in engine technology may lead to advancements that could influence the future of the Thrust Resolver Angle. As the aerospace industry continues to evolve, it is crucial to stay informed about these developments and their potential impacts on aircraft performance.

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