Questions tagged [altimeter]

The instrument which indicates the aircraft's altitude, usually based on atmospheric pressure, but sometimes on radar or GPS data instead.

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15
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4answers
17k views

How do aircraft altimeters calculate altitudes accurately while airborne?

While an aircraft is airborne, the local barometric pressure can change, causing an altimeter to no longer display the correct altitude. How are altimeters re-calibrated to display the correct ...
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2answers
15k views

How will the altimeter read in air colder than ISA?

When flying in air which is colder than ISA (International Standard Altitude), how will the altimeter read compared to true altitude? My manual says the altimeter will over read - why?
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When is QFE used?

When is QFE, instead of QNH, used for the altimeter setting? QFE: If you set the subscale of your altimeter to read ... millibars, the instrument would indicate its height above aerodrome elevation ...
17
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1answer
12k views

What is the difference between "sensitive" and "non-sensitive" altimeters?

In this answer reference was made to "sensitive" and "non-sensitive" altimeters. What is the definition of each, what are the differences, and why would one be used in preference to the other? And ...
10
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2answers
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Why isn't transition altitude standardized in Europe?

In the US, the transition altitude is standardized at 18,000ft, however in Europe it is different for every airport. Why is it not standardized like it is in the US? I could see situations where ...
17
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3answers
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What is the maximum altitude of barometric altimeters?

An altimeter works by sensing static air pressure. As altitude goes up, the pressure decreases. If I take a barometric altimeter up to space (e.g. up to satellite orbit), at what altitude does its ...
7
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2answers
1k views

How is non-standard OAT accounted for?

This pdf from Airbus has a chart from ICAO showing the amount of correction to be applied to altimeter readings for temperatures below 0°C. Do aircraft with flight data computers automatically ...
5
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1answer
1k views

Why would a Mode-C transponder report a different altitude than an altimeter/GPS?

This is related to a small single-engined plane. On a recent flight, the controller kept telling me that I was 300 ft higher than it appeared on my altimeter and GPS (which were in sync). This was ...
14
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2answers
13k views

How precise are altimeters?

How precise and how accurate are typical altimeters these days? That is, if two planes are flying (side-by-side, very near each other), and both altimeters show the same Flight Level, what is the ...
11
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1answer
5k views

Why is a TFR issued when barometric pressure exceeds 31.00 InHg?

Why does a barometric pressure above 31.00 InHg trigger a TFR?
3
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2answers
4k views

What is wrong about this interpretation of QFE and QNH?

I'm a little confused about the QFE and QNH definitions, and its application on aviation. I learnt that: $QFE$ = pressure measured by an altimeter which is adjusted to ground level (it gives a height ...
13
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2answers
14k views

Where did the terms QNE, QNH, and QFE come from?

In the aviation community (at least outside North America), the terms QNE, QNH, and QFE are used to describe standard pressure, local altimeter, and field elevation, respectively. But what is the ...
12
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2answers
3k views

Where does the altimeter measure from?

During the landing flare, the cockpit can sometimes be twenty/thirty feet or more above the rear landing gear, especially with larger aircraft. (source: valkaviation.com) In some aircraft, you can ...
9
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2answers
529 views

Who has the responsibility to make altimeter corrections in cold temperatures?

I work as air traffic controller in Asia and we refer to both ICAO and FAA regulations. As winter is coming, there is a debate on altitude correction (or altimeter correction?) for cold temperatures. ...
7
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2answers
717 views

How does an altimeter deal with the non-linear pressure gradient?

Altimeters work via an aneroid barometer to sense the atmospheric pressure. If I climb from 2000ft to 4000ft, the altimeter senses that the pressure has reduced by, let's say, 70hpa, and is calibrated ...
5
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2answers
406 views

Can RVSM safely be further reduced?

Since the world population shows no signs of slowing down its rapid increase, it's pretty safe to say that means we can only expect more concurrent flights as time moves forward. Is it physically ...
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3answers
10k views

What is the meaning of the crosshatch marking on altimeters?

What does the crosshatched area on an altimeter tell you? It's only visible when below 10,000 ft indicated altitude. Can't be terrain awareness, a lot of terrain around here is over 10,000 feet. ...
11
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2answers
2k views

How do radio altimeter systems compensate for objects on the ground?

My understanding of a radio altimeter is that it can provide more accurate altitude readings below the transition level. It occurred to me a number of days ago whilst sitting beneath the glide path ...
4
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2answers
1k views

What type of altimeter is this?

What type Altimeter is an SA-91? It has three pointers 100, 1000, 10000. Don't know if it is Kollsman. I can't find any info as far as repairing unit.
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2answers
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How are airspace violations detected?

Are airspace violations (e.g. entry to class B without clearance) based on primary radar and/or Mode C transponder, or something else? I read that Mode C altitude is based on pressure altitude, i.e., ...
10
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2answers
784 views

If left stationary at a specific height, would altimeter change the displayed value over time?

I have been reading a lot about how altimeters work, and from what I understood, most common altimeters are based of atmospheric pressure to calculate the altitude. The question that I still have ...
9
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3answers
47k views

How can I calculate QNH from QFE?

Can someone please explain in simple terms how to work out your QNH from QFE? For example, you take off at 0' but leave the circuit, what do you set the altimeter to? How do you know the QNH?
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How will flying through mountains cause altimeter problems?

There is an old warning on mountain flying that wind flowing through a narrow valley will cause Venturi effect, thus causing a drop in static pressure and making our little Cessna fly lower than ...
13
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4answers
10k views

What is the meaning of "altimeter three-zero-one-one"?

I've been listening to a lot of liveatc.net recently (mostly at CYVR). What does it mean when the ATC give an "altimeter" reading (usually around the 3000 area). Altimeter three-zero-one-one. I'm ...
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2answers
570 views

What does one do when the weather report has a bogus altimeter setting?

I saw a METAR for a nearby airport that had A2248 ... SLPNO in it with no maintenance indicator. Is the SLPNO a sign that the altimeter setting in the METAR is untrustworthy as well? How else does ...
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3answers
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When calculating takeoff performance why include airport elevation in pressure altitude?

When calculating the pressure altitude for aircraft performance I learned to calculate it the following way: Pressure Altitude = (29.92" - altimeter setting) * 1000' + elevation So at an airport at ...
5
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3answers
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How often is QFE set on an altimeter during flight?

In countries that use QFE rather than QNH (such as China), how often will a pilot set the QFE setting on their altimeter during flight? Is it only when they intend to land at an airfield, or does it ...
5
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1answer
484 views

Is true altitude vertical separation between airplanes dependent on temperature?

Does the "true" altitude vertical separation between airplanes (using the same altimeter setting) vary as the temperature changes? ( I fully realize that the "true" altitude of both airplanes is ...
3
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1answer
856 views

How does changing the altimeter setting in the US and elsewhere compare?

I have been trying to track down an answer to this question and I stumbled upon this website. Apologies if this answer is already out there. I have seen the FAR regulation, 14 CFR 91.121 - Altimeter ...
3
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1answer
398 views

Altimeter setting and pressure altitude

Student pilot here. I thought I was smarter than this, I’m struggling with this concept. I got the ASA test prep book and there’s a question asking what happens to the indicated altitude when the ...
2
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1answer
329 views

Altimeter disagreement. What's the crew procedure to deal with that?

The crew is facing a situation, in which, the altimeters indicate different altitude (the port and starboard ones - cpt´s and FO´s). Is there any procedure to perform an IFR landing? If we consider a ...
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1answer
213 views

What does setting an altimeter actually do to the altitude?

I have looked at probably 10 different webpages and re watched the Sportys video on altitudes, multiple times, but I have a very fundamental question, which I am unable to wrap my head around. Is my ...