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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Do ATC say "Climb to XXXX on standard" or "Climb to standard XXXX" or something else?

Do ATC say "Climb to XXXX on standard" or "Climb to standard XXXX" or something else? By "standard" I'm referring to altimeter pressure settings (set to standard pressure)...
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Why does aircraft weight influence position (installation) error in pitot-static systems?

I am a private pilot from Argentina studying to become a commercial pilot. In one of the books I was given to study, published by the Chilean air force, the there's a claim (in Spanish, page 36) that ...
Nahuel Prieto's user avatar
4 votes
3 answers
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What is the effect of wind on altimeter reading?

I am wondering is there any effect from wind on the altimeter reading? I think when the wind is blowing, the static pressure around the aircraft in flight will somehow change and this can impact the ...
AIRWAYLOVER's user avatar
5 votes
1 answer
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Why are flights not also restricted during abnormally low barometric pressure conditions

FAR 91.144 talks about restricting flight operations during abnormally high barometric pressure conditions. Why would there not be an identical restriction during abnormally low barometric pressure ...
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Should I add or subtract PA when calculating performance

I am planning a cross country and I wanted to know how would I calculate my PA for performance. If the elevation of my airport is 16ft and the altimeter setting for the day is 30.03 I subtract 30.03 -...
youngpilot's user avatar
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How precisely are pilots expected to be able to read altimeters?

I'm writing a program to practice reading three-hand analog altimeters. How precisely should a pilot be able to read one?
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Manual or other information regarding Kollsman Instruments B40331-10-276 altimeter

I just purchased a used altimeter from eBay because it'll look pretty on a shelf, and I may add a computer interface to it. However, I need help finding information on it. This (from what I've been ...
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is pressure altitude at different temperatures (different days) on the ground at the same airfield the same?

let's say we are at x-airfield which is at 0 MSL on the ground. We set the Kollsman window to 29.92 on a standard day, whatever the read is that would be the Pressure altitude, correct? (ideally zero ...
YamchaAviator's user avatar
14 votes
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5k views

What should I follow, if two altimeters show different altitudes?

My school airplane has a Garmin G5 Electronic Flight Instrument and round gauge altimeter, but they have almost 50ft differential. The G5 shows 50 feet higher on the same altimeter setting. So in IFR, ...
윤상우's user avatar
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Do altimeters still work in extreme angles of flight?

I've heard that the way the plane measures its altitude is to use a barometer to measure air pressure. Does the pressure at the static ports drop as the aircraft's speed increases? There is no ...
lotsof one's user avatar
2 votes
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Air density factor when calculating Airspeed

I am making my own attitude indicator / AHRS, like a Garmin G5. I am using two pressure sensors to measure altitude & airspeed via static /pitot lines. Now I know the formula for calculating ...
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In the International Standard Atmosphere/ICAO, what is geometric and what is geopotential altitude?

Read first before you start considering it a duplicate, please, as the similar questions didn't answer my question either. The usual standard atmospheres have two altitudes: the geopotential and the ...
Giovanni's user avatar
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What were the atmospheric models in the 19th century and early 20th century like, compared to the present-day ISA?

Atmospheric pressure has been used to determine the altitude a pilot (or a mountain climber as well) is at since the beginning of the age of ballooning. I find the following Wikipedia excerpt about ...
Giovanni's user avatar
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Is the ISA still up to date?

The Standard Atmosphere dates back to 1962 when Earth was colder. The 1976 update didn't make changes within 50 km altitude (the tropo- and stratosphere). It assumes 15°C at sea level, decreases until ...
Hidden User's user avatar
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If you are in a terrain escape maneuver, would you be able to see traffic above you displayed in the cockpit of airliners [closed]

nayed If you are in a terrain escape maneuver, would you be able to see traffic above you in the cockpit of big airliners
Yosef Jabbour's user avatar
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How many times does a pilot usually change local pressure while landing or departing?

The local air pressure (QFE, and therefore QNH as well) may change throughout the day. ATC will advise pilots of the new altimeter setting on a regular basis. How often do pilots truly update this ...
Yosef Jabbour's user avatar
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What is the legally accepted tolerance for altimeter errors under EASA for a VFR flight?

I have a discussion going on with a flying club member. He states that altimeters may have an error margin of up to +/- 200ft. Example: ATC instructs you to fly 1500 feet, you would still stick to ...
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What is that green rectangle next to altitude readout on Boeing aircraft?

Does anyone know what this green rectangle represents? It's from a Boeing 777 PFD. I can't find answers anywhere.
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Difference between "pressure levels raising on warm days causing lower IA" and "TA being higher than IA on warm days" [duplicate]

IA: Indicated altitude TA: True altitude I have seen this picture before: Concept 1 and I understand this. On cold days, the pressure gradient is shorter which means the indicated altitude at a ...
Jonathan's user avatar
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Which radar altimeters are susceptible to 5G C-band altimeter interference?

There is apparently a great deal of consternation over the pending expansion of 5G The emergency petition claimed that interference from the C-Band "will cause irreparable harm and jeopardize ...
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What does CPLD mean in aviation in general and on this altitude alerter?

I saw the shortcut CPLD on this altitude alerter from a Cessna 210, and could not work out what it could possibly mean: What does it mean on this altitude alerter, ...
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2 answers
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What is the purpose of the leaf spring in an altimeter?

What is the use of the leaf spring present around the partially evacuated aneroid capsule of sensitive altimeter.
Sourabh Jain's user avatar
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What is the minimum and maximum altitude reading for the average radar altimeter?

The valid range for latitude is -90 to 90 degrees. The valid range for longitude is -180 to ...
lolololol ol's user avatar
8 votes
2 answers
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What kinds of altimeter are used in modern airliners?

What's the mechanism of the altimeters in big jets?
Sachin Chaudhary's user avatar
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What are the three different altitudes shown in the Perlan II?

The Perlan II glider has two altitude indicators and an altimeter on the navi screen, each showing different altitudes: How is each of the altimeters different? One indicator certainly shows MSL and ...
Giovanni's user avatar
1 vote
1 answer
186 views

Is a balloon's record altitude measured from the top of canopy, the bottom of the basket, or some other point?

I wonder where exactly on the balloon is its altitude measured. By the time a space balloon reaches its maximum altitude it is extremely large, the higher the larger. The record altitude for a balloon ...
Giovanni's user avatar
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Is there a place where altitude while flying is negative?

while testing and working with avionics systems I have never seen an altitude near 0 or negative. Is there a place when flying above the Altitude tape shows -ve value ? Maybe while flying between ...
Huntkil's user avatar
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If a plane was put into a vacuum chamber, what would its altimeter read? [duplicate]

Just curious. What if you put a (general aviation or airliner) plane into a hard vacuum chamber? Would its altimeter simply read the highest possible altitude it could? That's rather impossible for ...
Giovanni's user avatar
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1 answer
584 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 ...
vcapra1's user avatar
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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 ...
rbsc's user avatar
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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 ...
Jesh Kundem's user avatar
37 votes
1 answer
5k views

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 ...
Sniper's user avatar
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1 answer
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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 ...
lemonincider's user avatar
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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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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 ...
Miguel Anaya's user avatar
3 votes
5 answers
3k views

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 ...
user7828137's user avatar
15 votes
2 answers
4k views

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....
GeckoFox1001's user avatar
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6 votes
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501 views

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 ...
Trevor Johns's user avatar
1 vote
1 answer
2k 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 ...
Namster's user avatar
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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, ...
Devil07's user avatar
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6 votes
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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 ...
st2000's user avatar
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4 votes
3 answers
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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 ...
Melih Durmaz's user avatar
4 votes
1 answer
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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 ...
rbsc's user avatar
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34 votes
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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 ...
Manu H's user avatar
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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 ...
Transcendental's user avatar
1 vote
3 answers
3k views

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 +/- ...
saigafreak's user avatar
3 votes
2 answers
2k views

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. ...
Ondrej Telka's user avatar
2 votes
2 answers
1k views

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 ...
Hamid's user avatar
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8 votes
1 answer
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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 ...
talkanat's user avatar
2 votes
2 answers
2k 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 ...
SillySquishy's user avatar