Final answer:
Vref speed must be higher at a high density altitude airport compared to sea level due to reduced air density, requiring higher speeds to generate adequate lift for the aircraft. This is linked to principles such as viscous drag and buoyant force affecting an object's terminal speed in different fluid densities.
Step-by-step explanation:
Impact of High Density Altitude on Vref Speed:
When flying into a high density altitude airport compared to a sea level airport, the Vref speed, or the reference speed aircraft use to approach for landing, will be affected. This is due to the air density variation at different altitudes. At higher altitudes, such as those you would encounter at a high density altitude airport, the air is less dense compared to sea level.
Since lift is partly a function of air density, a plane must travel at a higher speed at higher altitudes to create the same amount of lift as it would at lower altitudes where air is denser. This is analogous to how the terminal speed of an object falling through a fluid will increase if the fluid's density decreases, as noted in the principle that includes factors like viscous drag and buoyant force. For example, at an altitude where air density is one-fourth that at sea level, the speed of air moving over the wing must be greater to provide the necessary lift for safe flight operations. Consequently, Vref speed at a high density altitude airport will be higher than at sea level for the same aircraft under the same conditions.
As shown in Figure A4, The Altitude-Air Density Relationship graphically demonstrates how air density decreases with an increase in altitude, thereby necessitating a higher Vref speed to compensate for the reduced lift generated by the less dense air.