Questions tagged [altimeter]

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

Filter by
Sorted by
Tagged with
2
votes
1answer
82 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 ...
2
votes
2answers
75 views

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?...
9
votes
3answers
306 views

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 ...
5
votes
1answer
177 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 ...
3
votes
1answer
106 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: ...
6
votes
1answer
445 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 ...
-1
votes
1answer
96 views
4
votes
2answers
302 views

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 ...
3
votes
1answer
108 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 ...
1
vote
0answers
32 views

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 ...
5
votes
3answers
689 views

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 ...
5
votes
3answers
672 views

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 ...
5
votes
1answer
275 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 ...
2
votes
1answer
126 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 ...
2
votes
2answers
2k 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 ...
5
votes
2answers
243 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 ...
5
votes
1answer
737 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 ...
0
votes
1answer
1k views

How altitude changes with changed QNH?

How the AGL altitude changes with changed QNH? I'd like only to confirm or correct my intuition.. Airplane is maintaining certain FL with some QNH, its instruments are showing some AMSL. Now the ...
8
votes
1answer
717 views

From which aircraft does this vintage altimeter come from?

I bought this vintage U.S. Navy Kollsman altimeter at a market in Bangkok, Thailand. Unfortunately, I don't have any info other than what you see in the photos. It's a Kollsman altimter and the ...
1
vote
1answer
326 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 ...
3
votes
0answers
216 views

How to get the true altitude in non-standard temperature using a regular barometric altimeter? [duplicate]

I wondering how can we get the true altitude with non standard temperature on regular barometer altimeter, as we know that if we set Kollsman window to the current local setting the altimeter SHOULD ...
5
votes
1answer
2k views

Why is Landing Altitude displayed in amber on B777?

When I set the landing altitude manually, an amber LDG ALT and Landing Altitude EICAS message is displayed. There are no failures nor has the landing altitude been set incorrectly. Why do I still ...
9
votes
3answers
1k views

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 ...
3
votes
1answer
107 views

What is the altitude of the nose vs tail in airplane flight?

Suppose you have an airplane flying level on a long flight. Now suppose you place one altimeter sensor in the tail, and one in the nose. Suppose you record and store these values independently (...
11
votes
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 ...
5
votes
1answer
219 views

Is it possible to get the QNH value in Austria using a web service?

I got a altimeter sensor which can be connected to a computer and can be adjusted by the QNH! I need the QNH for Austria, I figured out that the current QNH of the airports are streamed via radio. ...
9
votes
2answers
370 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. ...
2
votes
1answer
424 views

How are altimeter settings estimated?

So, I spotted another weird METAR from the same place that spawned the first one I asked about (it's a USAF base if you're wondering what kind of 'drome it is): K... 060846Z 00000KT 10SM OVC002 18/...
4
votes
2answers
8k 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?
3
votes
1answer
701 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 ...
11
votes
1answer
3k 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?
5
votes
3answers
1k views

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 ...
1
vote
1answer
276 views

What are “ground-based navigation systems which provide vertical guidance” and how do they compare to altimeters?

I am a total layman when it comes to aviation but for a school presentation I am trying to understand the reasons why Air Canada 624 crashed while trying to land on runway 05 at Halifax (CYHZ). I have ...
6
votes
2answers
1k views

What do the pointers on a Kollsman altimeter indicate?

In this thread: What type of altimeter is this? there are 3 images of altimeters that have a pointer that moves around the outside diameter of the scale markings and they have another pointer that ...
3
votes
2answers
3k 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 ...
4
votes
1answer
257 views

Is it OK practice to use one altimeter on QFE and one on QNH (local flight, dual altimeters)?

PPL student, wondering on how this practice is viewed. The aircraft I'm learning to fly in has a small Dynon EFIS which displays horizon, airspeed, heading & altitude. It also has a regular ...
6
votes
3answers
2k views

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 ...
15
votes
3answers
2k views

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 ...
12
votes
2answers
2k 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 ...
7
votes
3answers
30k 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?
7
votes
1answer
829 views

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 ...
11
votes
4answers
6k 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 ...
41
votes
1answer
3k views

How can an altimetry system error during cruise (500 ft at 35000 ft high) cause an insufficient fuel situation?

So my boss gave me a question today as my daily quiz: Let's say an A321 is cruising on a 6-hour flight. It reaches FL350 30 minutes after take-off. After another 8 minutes there's a discrepancy ...
8
votes
3answers
4k views

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 ...
6
votes
2answers
471 views

Can a change in altimeter setting make you change the airspace?

If you are at 17999 MSL VFR, you twist in 29.92 into the altimeter, and it raises your altitude to above 18000, did you bust the class A? Then theoretically, could you be in class A airspace with a ...
4
votes
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.
9
votes
2answers
9k views

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 ...
7
votes
2answers
461 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 ...
2
votes
1answer
286 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 ...
3
votes
1answer
420 views

Why is the Inertial Reference System not used to determine true altitude?

Given three very accurate laser gyros and accelerometers I believe the Inertial Reference System (IRS) should be as accurate in determining true altitude as it is in determining lat/long, providing ...