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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242 views

How can I compute indicated altitude?

I would like to compute what an altimeter would display given a true altitude and atmospheric conditions. Specifically: Given: True altitude, in feet Outside air temperature, in degrees C Local ...
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Station pressure vs. reported altimeter

I must be missing something big. Page 12-5 of the PHAK tells me that a station at 5,000 feet above sea level would convert its 24.92 pressure reading to 29.92. I understand that this helps to track ...
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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 ...
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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 ...
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333 views

Relation between altimeter setting (QNH) formula and the barometric formula

I'm searching for a reliable source for a formulization of the QNH adjustment to the barometric altitude. I found this document from weather.gov that gives a formula for the Altimeter Setting, which ...
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Why does a radar altimeter show negative values on the ground?

This applies to the Airbus 320 or Boeing 737, among others: Although it is useless on ground, the radar altimeter will repeatedly display a value (including negative) for a specific runway and airport ...
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113 views

Is the true altitude always lower than the indicated altitude as long as a correct local altimeter (QNH) is set on the altimeter?

Given the fact that the altimeter setting is corrected for the temperature of the airport, on the condition that a correct local altimeter setting (QNH) has been made to the altimeter, is the true ...
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95 views

Is there a regulation that defines when to use QFE or QNH for landing?

Is there an EASA regulation that says to use QFE or QNH when landing?
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519 views

What is the standard temperature used in this true altitude equation?

The control tower of a certain airport with true altitude of 2000ft informs the pilot that QNH is 900hPa and the temperature at the airport is -10 degrees Celsius. The airplane is at FL300 (vertically ...
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Is this vintage altimeter from the Cuatro Vientos?

My father who was a pilot, passed away some years ago and I have a vintage altimeter that he told me someone gave him. They assured him that it belonged to the Cuatro Vientos airplane, but I'm not ...
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Why doesn't temperature affect Pressure Altitude?

In this picture: it states the tops and bottoms of the 3 columns of air have the same pressure. This explains the error in altitude indications given in a non-standard temperature. Pressure only ...
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Why can't you just set the altimeter to field elevation?

Why do you have to put the current altimeter setting in the kollsman window? Why can't you just set it to field elevation when you're on the ground? I understand why you would have to do it in the air....
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Which altimeter setting is used to define airspace boundaries?

Let's say that we're flying VFR over the top of Class D airspace at 3,000 feet. The Class D extends up to 2,900 feet - we're above it, but just barely with a 100' buffer. We're also talking to ...
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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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121 views

Calculation of temperature correction for altimeter

I try to calculate the correction of cold temperature for altimeter , i use for this the equation 24 of the Engineering Sciences Data Unit (ESDU) publication but it give me very high number . if i ...
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202 views

If an aircraft has two altimeters what is the allowed difference between them?

If an Altimeter must be within +/- 75 of known field elevation, and the aircraft has two altimeters, one could be +74 while the other could be -74 and both would be within 75 of known field elevation, ...
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Why are the airport pressure values for "altitude" (inHg) and "sea level" (mb) slightly different on the NOAA web sites?

If one looks, for example, at the NOAA web site for Denver International Airport we see (at the time of posting this question) the Pressure/Altimeter is 29.78 inHg, the Pressure/sea level is 1006.1 mb ...
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296 views

How do barometric altimetry systems compensate for nonstandard pressure lapse rates?

Barometric altimetry relies on atmospheric pressure dropping at a steady rate with altitude, starting from a measured ground-level pressure. This, in turn, relies on atmospheric density dropping at a ...
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402 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 ...
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How is altitude reached by aircraft flying above the stratosphere measured?

Aircraft flying above the stratosphere (above 30km) are rare, but there is still the X-15 and the spaceship two. For those aircraft, maximal altitude is measured to within 500 ft. As described in this ...
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IFR requirement for altimeter question (i.e. +/- 75 feet) [closed]

What if the ATIS/AWOS/ASOS results in a very low or very high altimeter setting (i.e. barometric pressure)? Surely this setting will result in an altimeter setting way outside the envelope of the +/- ...
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Why did the altimeter in an F-16 jump suddenly as it passed through Mach 1?

In this video, Destin — the creator of YouTube channel Smarter Every Day — rides in an F-16 with a USAF Thunderbirds pilot. If you start watching the video at the 11:06 mark, you will see what happens ...
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How is Altitude/QNH defined state when passing transition altitude?

Let's say an airplane is climbing towards transition altitude (TA = 5000 ft), and it has it's altimeter set to QNH = 1030 hPa. ...
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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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Did the Stuka Ju-87 really have a radio altimeter? If so, when?

This is what Wikipedia says near the end of its radio altimeter article: The radio altimeter first showed up in the German Junkers Ju-87 "Stuka" dive bomber which was equipped with one for ...
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What is the main reason why cruise flight in the transition layer is prohibited?

What is the main reason why cruise flight in the transition layer is prohibited? For example if we have a separation of 1000 ft between transition altitude and transition level, why should we not ...
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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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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. ...
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What would the altimeter indication be through a cold front?

Cold air is heavier than hot air because of its greater density, so the QNH of an airport inside a cold front would be higher. Flying towards the cold front would be, "low to high, hello sky". But I ...
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236 views

Who is responsible to check for radar-altimeter disagreement?

I have searched the site but failed to find a similar question. I know that modern civil aircraft are equipped with multiple radar altimeters. Question is: In the unlikely event of those outputting ...
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577 views

What does the altimeter indicate if it's at a certain elevation

The purpose of the altimeter is to show the pilot the altitude and the pressure above a fixed level. It uses barometric pressure and is 29.92Hg in ISA conditions. What I dont understand is, how can ...
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548 views

Why does the QNH of an aircraft change or need to be changed?

This is mainly a 3 part question. First, is it the QNH of of the aircraft? of the aerodrome? of the region or area? Or am I understanding it wrong my looking at it like that? If the QNH is set ...
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Why is ISA Standard pressure 1013.2 not used for contour charts instead of QFF?

I am confused because QFF being actual mean sea level pressure is subject to change why would we use it for mapping terrain? Does this mean the height of a given terrain changes with the change in QFF?...
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How can true altitude be calculated from pressure altitude, temperature and altimeter setting?

The manual that came with my Jeppensen E6B has the following sample... If an aircraft is flying at 12,500 feet with an outside air temperature of -20C and the altimeter is set on 30.42 inches of ...
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530 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. ...
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293 views

Altimeter shows 100 foot drop when power is added. Is this a leak in the static system or broken altimeter and how long will the fix take?

My instructor and I were preparing for my Private Pilot Check ride today when we noticed that the analog altimeter would suddenly lose 100 feet when we added power. The only way I can think to ...
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Vintage army Kollsman altimeter - any info?

I have a vintage Kollsman altimeter A.C. U.S. Army. I can't read the text on the front because of the needle arms are in the way, but might state: Type 5 Serial No A 464. Back plate is very hard to ...
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214 views

How do altimeters cope with varying lapse rate?

How do barometric altimeters measure altitude above atmosphere datum if the laps rate of the pressure is not uniform, not constant? Imagine these lines representing pressure lapse rate: ...
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1k views

Why are/were three-pointer altimeters so prone to being misread?

The three-pointer dial altimeter (with a shortest pointer indicating tens of kilofeet, a short pointer indicating kilofeet, and a long pointer indicating hectofeet), the most instantly-recognisable ...
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Why, and how, are barometric altimeters accurate enough for approach and landing?

The barometric altimeter is used as the primary altitude indicator during approach and landing right up until the aircraft crosses the threshold (after which the radar altimeter takes over and makes ...
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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 ...
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If the 10000ft pointer is reading 5 (50000ft) when you are at 10ft how do you get it back to zero [closed]

Kollsman altimeters 10000ft pointer adjustment
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How does the mounting surface flatness affect radio altimeter reading?

It is recommended that the antennas be installed on flat surfaces. For some UAVs, the bottom of the fuselage is very narrow and sharply curved away from the antennas. How does it affect the ...
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How accurate is the barometric altimeter in the Tu-154?

If the Smolensk disaster was to be traced down to a single decision (other than attempting landing in the first place), it would probably be the choice of radio altimeter to control altitude over a ...
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What’s the setting range altimeters can handle?

What’s the setting range altimeters can handle? Is there a standard requiring a certain range for aircraft to be certified? Are there many occasions where a QNH is so high or low that airplanes have ...
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Are altimeters calibrated to ISA geopotential altitude or ISA geometric altitude?

Altimeters convert a pressure measurement to an indication of altitude. When set to standard pressure setting (1013.25 hPa / 29.92"Hg), they assume the atmosphere is according to the ICAO Standard ...
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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 ...
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194 views

Barometric altimeter data during high vertical g-forces?

I’m contemplating that that under high vertical acceleration (such as the maximum limit of 2.5g for commercial airplanes), that hydrostatic atmospheric pressure wouldn’t be a complete model. Wikipedia ...
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5k views

When flying into an area with colder air, how will the altimeter read compared to true altitude? [duplicate]

When flying into an area with colder air, how will the altimeter read compared to true altitude? Air expands as the temperature increases and it compresses when the temperature decreases, shall I ...
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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 ...