Describe the term pressure altitude (PA); include in your discussion what causes

Question

Describe the term pressure altitude (PA); include in your discussion what causes PA to change. Describe what will physically happen to an aircraft that is flying on a long cross country flight, from an area of relatively high pressure to one of lower pressure, if the pilot does not adjust his/her altimeter setting along the route of flight. How might this affect an aircraft that is flying in mountainous terrain (close to mountain tops), solely by use of instruments (in the clouds), and upon landing at its destination on an instrument approach (flying in the clouds)?

Explanation / Answer

Earth’s atmosphere is composed of air molecules and till troposphere there is good composition of the air molecules. On the sea level, the weight of the air above presses down and causes an air pressure. Also at the ground level density of air is high. If we go higher in the sky density of the airs sinks. High density results in high pressure. That’s why at the sea level pressure is high and on top of mountains low-pressure prevails. Another factor which affects the pressure is temperture. the high and low-pressure system across the area causes the wide scale movement of air (upward / downward / horizontally). So that pilots, meteorologists are using common reference point at sea level in the standard atmosphere was calculated to be 1013.25 hpa or 1 atm .

That is pressure altitude is the altitude above or below the standard pressure 1013.25 hpa.

Altimeter is an instrument which gives the current height of the plane by measuring the current height of the plane by measuring the change in atmospheric pressure with respect to the standard pressure at sea level. this standard pressure will change from place to plece. so if the pilot does not change the standard pressure setting in the altimeter, while going from high pressure to low pressure, the actual height will be less but altimeter will predict the height higher than the actual value since it is based on pressure change.

if the altitude is predicted wrongly, there is a chance that the flight crashes with the mountain.

if the distance between flight and land is not calculated perfectly, there is obvious chance of flight crash.

Hence altimeter setting is very important and it should be done time to time with the information from local air ports.

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