Under which condition would an airplane typically have its maximum L/D ratio?

An airplane typically achieves its maximum lift-to-drag (L/D) ratio during the cruise phase. This is due to the fact that, in cruise flight, the aircraft operates at an optimal speed and altitude, where both lift and drag are balanced to provide the most efficient flight condition. In this state, the airplane maintains level flight with the least amount of induced and parasitic drag, allowing it to cover the maximum distance for minimal fuel consumption.

In contrast, during stall conditions, the airflow over the wings becomes turbulent, leading to a significant increase in drag and a decrease in lift, resulting in a very low L/D ratio. The approach phase involves maneuvering and may involve changes in speed and configuration (such as deploying flaps), which does not ideally optimize L/D. Similarly, the climb phase requires higher thrust and often operates at a higher angle of attack, which again results in increased drag and a lowered L/D ratio compared to optimal cruising conditions.