Which atmospheric conditions will cause the true landing speed of an aircraft to be the greatest?

Which atmospheric conditions will cause the true landing speed of an aircraft to be the greatest?

• A. Low temperature with low humidity
• B. High temperature with low humidity
• C. Low temperature with high humidity
• D. High temperature with high humidity

Answer: (D)

The true landing speed is driven by air density: for a given weight and wing, the speed needed to generate enough lift increases as density decreases. This comes from the lift equation, which shows the required true airspeed is proportional to the square root of weight over density (V ∝ sqrt(W/(ρ S CL))). So, when the air is less dense, you must fly faster to produce the same lift. High temperature and high humidity both reduce air density: hot air is less dense, and moist air is lighter than dry air because water vapor lowers the mean molecular weight of the air. Together, they create the lowest density among the options, which means the aircraft must achieve a higher true airspeed to land safely. Therefore, the condition with hot, humid air yields the greatest true landing speed. In cooler or drier conditions, air density is higher, so the required true airspeed for the same weight and configuration would be lower.

The true landing speed is driven by air density: for a given weight and wing, the speed needed to generate enough lift increases as density decreases. This comes from the lift equation, which shows the required true airspeed is proportional to the square root of weight over density (V ∝ sqrt(W/(ρ S CL))). So, when the air is less dense, you must fly faster to produce the same lift.

High temperature and high humidity both reduce air density: hot air is less dense, and moist air is lighter than dry air because water vapor lowers the mean molecular weight of the air. Together, they create the lowest density among the options, which means the aircraft must achieve a higher true airspeed to land safely. Therefore, the condition with hot, humid air yields the greatest true landing speed.

In cooler or drier conditions, air density is higher, so the required true airspeed for the same weight and configuration would be lower.