How we can calculate Altitude of an Aircraft?

Aircraft don’t really exactly know their altitude. They fly at a pressure, that is indicated as an altitude via equations in the Standard Atmosphere.

What is the altitude of a plane in flight?

When flying a plane, the pilot needs to know exactly how high above the earth the plane is traveling, a measurement that is called altitude.

Types of Altitude:

Indicated Altitude

Let's start with the easiest - indicated altitude is simply the altitude you read directly off your altimeter. If uncorrected for pressure changes, your altimeter won't be very useful.

True Altitude

True altitude refers to the height of an aircraft above sea level. This type of altitude is measured in terms of “feet above mean sea level".

Pressure Altitude

Pressure altitude is a measurement of the aircraft’s altitude above a standard datum plane Pressure altitude is also used in many flight planning calculations, including determining takeoff and landing distances.

Density Altitude

Density altitude is pressure altitude corrected for non-standard temperature. Now that summer is almost here, you probably noticed your airplane not performing as well. That's because with hot temperatures, density altitude increases and your airplane "feels" like it's flying at a higher altitude.

Less air mass flowing over your wings prevents you from generate as much lift, and less oxygen mass in your cylinders prevents you from burning as much fuel, meaning less power. Decreasing air density decreases performance, so be careful on hot days at high altitudes.

Absolute Altitude

Absolute altitude refers to the actual distance the aircraft is flying in relation to the ground and is expressed in “feet above ground level.” This type of altitude is generally determined using a radar altimeter, which measures how long it takes radar signals to reach the ground and reflect up to the plane. While absolute altitude is primarily used by large aircraft and not smaller aircraft.

Determining Altitude of an Aircraft??

Altimeter, instrument that measures the altitude of the land surface or any object such as an airplane.

Two Types Altimeter we use in Aircraft:

1. Pressure altimeter
2. Radar Altimeter

Pressure altimeter

The pressure altimeter operates through the response of trapped air within the instrument to changes in atmospheric pressure. The atmosphere surrounding the earth exerts pressure because of its weight, decreasing at a predictable rate as altitude increases. The pressure altimeter is a barometer that senses changes in atmospheric pressure and, through a gearing mechanism, converts the pressure to an altitude indication in number of feet

Who invented them?

Pressure altimeters were invented in the 1920s by German-born engineer Paul Kollsman, who was granted US Patent #2,036,581, Level flight indicator in April 1936. 

Radar Altimeter

 The radar altimeter, also known as radio altimeter, provides a continuous indication of aircraft height above the ground. The system is a "downlinking" device which accurately measures the distance between the aircraft and the highest object on the terrain. The time interval between a transmitted and received radio signal is automatically converted into an absolute altitude reading. The radar altimeter shown in Figure has a dial type readout. 

 

The radar altimeter has three main functions. 

• 1:Serves as a ground proximity warning device. 
• 2:Accurate cross-check for the barometric altimeter. 
• 3: It gives the pilot rate information on the progress of the final approach and an accurate indication and warning when reaching the "MDA" (Minimum Descent Altitude) or "DH" (Decision height) during instrument approaches.

All radar altimeters operate on a radio frequency of 4300 MHz.

Last but not Least Aircraft altimeters are subject to the following errors and weather factors:

• Instrument error.
• Position error from aircraft static pressure systems.
• Nonstandard atmospheric pressure.
• Nonstandard temperatures.

Some Corrective action for errors at glance:

The standard altimeter 29.92 inches Mercury (“Hg.) setting at the higher altitudes eliminates station barometer errors, some altimeter instrument errors, and errors caused by altimeter settings derived from different geographical sources.

How we can calculate Altitude of an Aircraft:

The pressure altitude can be determined by any of the three following methods:

1. By setting the barometric scale of the altimeter to 29.92 "Hg and reading the indicated altitude.
2. By applying a correction factor to the indicated altitude according to the reported altimeter setting.
3. By using a flight computer.

Pressure Altitude:

Formula:

Pressure Altitude = [(29.92 - Barometer current indication) * 1000] + Current field elevation.

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