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Question
Dear Prof Steve

Do the altimeter Flight instrument indicates with accuracy the plane Altitude from the ground level to the pilot?.

How does the Altimeter instrument measure the Altitude?.

Thanks & Regards,
Prashant S Akerkar

Answer
Hello Prashant,

There are different technologies used in various aviation altimeters. The most common type in private planes measures the atmospheric pressure and calculates altitude using the ratio of the standard sea level pressure and the measured pressure. More sophisticated models of that general type require dialing in updates of actual local sea level pressure which take temperature and weather systems into account. Most military and passenger planes measure distance to the ground via radar.

So the answer to your first question is no - if your altimeter is a standard pressure altimeter. The pilot/navigator is required to know their location so that they can find on a map or chart how much the ground is above sea level. A radar altimeter and some other high tech types (see the link below) can tell you distance to the ground.

The first paragraph above gives the answer to your second question.

For additional information, see
https://en.wikipedia.org/wiki/Altimeter

I hope this helps,
Steve

Physics

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Steve Johnson

Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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