How does the best rate of climb change with increasing altitude?

At higher altitudes, the density of the air decreases, which directly affects the performance of the aircraft's engines and overall lift generation. As altitude increases, the thrust produced by the engines typically reduces due to the lower air density, leading to a decrease in the overall power available to climb. This reduction in thrust means that, while the aircraft may be able to maintain level flight or even cruise efficiently at high altitudes, the performance in terms of climbing becomes less efficient. Additionally, the decreased air density also means that the lift generated by the wings is lower at the same angle of attack compared to lower altitudes.

Thus, the best rate of climb, which ultimately depends on the excess thrust available versus drag, declines as altitude increases. This relationship exemplifies the balance between thrust and drag, highlighting why the best rate of climb decreases with increasing altitude.