When flying for endurance, a helicopter is flown at the speed and height that will ensure:

• The maximum airborne time for a given amount of fuel, or
• The minimum fuel consumption for a given amount of time.

A helicopter is flying with the Maximum Endurance speed when the primary concern is just to remain in the air, as much as possible (such as during holding), and not cover the greatest distance (range).

Thus, in cruise, maximum endurance is not affected by wind.

The factors that may affect the maximum endurance in cruise are the following:

• Altitude: The optimum altitude for endurance is where the engine operates most efficiently, and any increase in altitude requires greater rotor thrust for a given speed, which can affect endurance.
• Speed: The speed for maximum endurance is the speed at which the aircraft uses the minimum amount of fuel to stay airborne for the longest time. This speed is known as the minimum power speed (V_MP), which is the point at the bottom of the power curve, where the power required is the least. Flying at this speed ensures that the aircraft consumes the least amount of fuel, thereby maximizing endurance.
• Variation in fuel consumption: If fuel consumption increases, due to factors, such as increased power requirements, or less efficient engine operation, the aircraft will consume fuel more quickly, reducing the time it can remain airborne.
• Helicopter's mass: An increase in mass requires greater rotor thrust to maintain a given speed. This increased thrust demand results in higher power requirements, which in turn leads to increased fuel consumption. As a result, the helicopter will consume fuel more quickly, reducing the time it can remain airborne and, thus, decreasing maximum endurance.