in Airbus A320, Pilot Notes

What is the reason for setting maximum climb thrust lower than maximum continuous thrust?

Maximum climb thrust being less than maximum continuous thrust for some airliners is due to several reasons:

Runway Length and Weight Limitations:

Aircraft need to accelerate to takeoff speed within a limited runway length. At or near maximum takeoff weight, this distance could be significant. In cases where the runway is short, the aircraft may need to reduce weight to ensure a safe takeoff. Additionally, obstacles like mountains or buildings may necessitate using maximum thrust until the aircraft is clear of them.

Engine Wear Considerations:

Engine wear is influenced by both heat and time. Higher thrust settings generate more heat, which can shorten the engine’s lifespan. To mitigate this, most engines have a time limit associated with higher thrust settings, such as during takeoff and initial climb.

Fuel Efficiency:

Fuel burn is not linearly proportional to thrust. Once the aircraft has climbed sufficiently to clear obstacles, it no longer requires maximum thrust, allowing for a shallower climb angle and improved efficiency.

Engine Efficiency and Wear Reduction:

Reduced thrust settings not only enhance fuel efficiency but also reduce wear on the engine. This allows the aircraft to operate more efficiently over its lifespan.

In most cases, maximum climb and maximum continuous thrust are synonymous, with the latter being the more commonly used term. However, in instances where maximum climb thrust is specified, it is typically lower than maximum continuous thrust due to considerations such as engine wear and efficiency.

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