Why do we use pressure altitude for performance?

A number of factors (altitude/pressure, temperature and humidity) influence air density. A higher altitude, low pressure area, higher temperature and high humidity all have one result: they lower the density of the air. And as a result of that: a reduction in aircraft and engine performance.

Why do pilots ask for altimeter?

In order to ensure an accurate reading the local air pressure is passed to the pilots by ATC. The pilot will then input this into their altimeter to recieve a correct reading.

What is the effect of altitude on power required?

Here we see that since the density at altitude is less than the density at sea level that the density ratio σ is less than one for any altitude above sea level. This means that the parasite power required decreases as the altitude increases but the effective induced power required increases as the altitude increases.

How do pilots know their altitude?

The primary altitude measurement device for a pilot is an altimeter. The altimeter measures the atmospheric air pressure outside of the airplane and gives the pilot an idea of how high they are flying. It’s up to the pilot to calibrate the altimeter because atmospheric pressure changes often due to the weather.

How does an aircraft know its altitude?

Altitude can be determined based on the measurement of atmospheric pressure. The greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter.

How does pressure change with altitude?

Pressure with Height: pressure decreases with increasing altitude. The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels.