76

If the aircraft is cruising at FL350 it is operating in Reduced Vertical Separation Minima (RVSM) airspace (between FL290 and FL410). With an altimetry discrepancy between the two altimeters of more than 245ft, the aircraft is no longer RVSM approved. It shall therefore descent or climb out of the RVSM altitude block. For the Airbus A321 the operating ...


25

Altimeters are calibrated to a standard atmosphere model (International Standard Atmosphere, ISA). What the altimeter shows you is the vertical distance between the altitude equivalent to your current pressure (pressure altitude) and a reference "pressure altitude". The reference pressure altitude is set in pressure units (hPa or In. Hg) on the altimeter ...


24

Objects on the ground are negligible because the radio altimeter is not designed nor used to such high precision. There are several uses of the radio altimeter. The first one is for timing the flare during the last portion of the landing. Since the flare maneuver starts after the aircraft has crossed the runway threshold, at this time the aircraft is over ...


19

It is called "standard pressure" because 29.92 In-Hg (or 1013.25 hPa) is the standard atmospheric pressure at sea level according to both the ISA (International Standard Atmosphere) and the US 1976 Standard Atmosphere. Below 18,000ft, local altimeter settings are used because you need to know how high you are above terrain, or whether or not you're at the ...


18

All altimeters are "sensitive" to some extent (an "insensitive" altimeter would be one where the internal pressure-sensing mechanism has failed: the pointer wouldn't ever move). What the FAA calls a "sensitive altimeter" is simply more sensitive than a regular (now often called non-sensitive) one: Non-Sensitive altimeters have a 1000-foot scale (200-foot ...


16

The Boeing 777 is a very automated aircraft. The takeoff altitude, landing altitude, and cabin pressurization altitude are all automatically set when you enter the departure airport and destination airport in the Flight Management Computer. The EICAS message ALT LDG appears when the FMC is not controlling the landing altitude. This can be caused by one of ...


15

While Accuracy and Precision are closely related, they're not the same thing. In the context of your question both are important: Accuracy In the US altimeters are broadly required to comply with FAR 43 Appendix E limits for accuracy (technically this is regulatory for IFR flight, but TSO'd "sensitive altimeters" will generally meet these requirements - at ...


15

That is a QNH altimeter setting in inches of mercury, with the decimal omitted. So in the case given, that is a QNH of 30.11.


15

It depends on the altimeter's design and certification. An example for a modern analog (aneroid) altimeter is this $5,000 Mid-Continent model. Its certified range is -1,000 to +20,000 feet, this is a reading you can depend on. The actual mechanical range is -15,000 to +50,000 feet. An RVSM altimeter working off multiple sources and an air data computer ...


14

It looks like the actual date is 1942. The 'Nachtschlachtgruppen' aircraft were given Ju 87 D aircraft with numerous upgrades including the FuG 101 radio altimeter. This would make sense because to use the regular contact altimeter the pilot must have knowledge of the height of terrain above sea level and then add to that when preparing his aircraft for ...


13

The transponder usually uses its own pressure reading, not what is set in the pilot's altimeter. So to prevent cheating as you describe, it is inspected and calibrated every 24 months. Tampering with it would be difficult to do on the fly because you'd have to adjust it based on the current atmospheric conditions and what altitude you want to seem to fly at. ...


12

It looks like the crosshatch (or barber pole) indicator doesn't have a consistent meaning (a similar marking is used on some airspeed indicators, by the way). I found several different examples of when it can appear: Below 10,000' (FAA PHAK; Army RC-12H manual) Below 15,000' (instrument service catalogue) Below 16,000' (another instrument catalogue) Above 0'...


12

The TSO for Air Data Computers is TSO-C106. It specifies for the minimum performance standard "SAE Aerospace Standard 8002, Air Data Computer - Minimum Performance Standard." From AS8002: 3.6 Altitude Reference: Calibration of the static air sensing mechanism for pressure altitude outputs (including baro-corrected if supplied) shall be to the ...


12

A difference of 1 hPa results in an error of 27ft in the altimeter. To have the altimeter showing 3000ft when the aircraft is actually at sea level, the altimeter must be off by 111hPa. Standard air-pressure at sea level is 1013 hPa (that's converted to 29.92 inHg for you Americans). For comparison, the pressure in Hurricane Katrina reached as low as 902 ...


11

It replaces to 10 thousands digit, evidently because X9000 has been found to be easier to read than 09000 or just blank space before the 9000. That crosshatched area would also scroll to display "NEG" if the altimeter is displaying an altitude below zero feet (i.e. Below sea level or below the reference datum plane).


11

It is called "standard pressure" because at an altitude of mean sea level (mean of all tides low to high) averaging the air pressure across equator to pole, winter to summer, over land and sea and day to night you get an average pressure that will register on the barometer at around 29.92 inches of mercury.


11

It uses a model called The International Standard Atmosphere (ISA) - so may be inaccurate if you don't have one of those to fly through :-)


11

Air expands as the temperature increases and it compresses when the temperature decreases. image source: aviationweather.ws When it is colder than ISA, the air column is compressed and therefore you are flying lower than the altimeter is indicating. In other words: the altimeter will over read in cold air. So to fly safely over an obstacle at a cold day,...


10

QNE, QNH, and QFE are Q Codes - the Q Codes are designed for telegraph (or radiotelegraph) use where information is transmitted in morse code and brevity is essential (e.g. "QNH KJFK 2992 INS" is much shorter to tap out in morse code than "JFK Altimeter 29.92 inches of mercury") They are still used in verbal communication (radiotelephone), though much less ...


10

You are correct in both regards -- as Terry's comment points out, an undisturbed pressure altimeter's reading (imagine one sitting on a bench outside the local hangar) will change with the local barometric pressure. TSO'ed "sensitive altimeters", i.e. ones with a hundreds pointer, not just a thousands, are required to have a knob and window, called a ...


10

It is used in aerobatic competition. It is much safer and easier to read AGL altitude directly from the altimeter than to attempt to do the arithmetic immediately prior to performing a maneuver. I normally fly out of a field at an elevation of 1000'. If I were to fly a contest in Colorado where field elevation is 8000' or higher, my altimeter will show an ...


9

IRS will drift over time. Decision altitude is 200ft for ILS CAT I approach. 0.5nm drift is not to much for navigation but it will be huge difference in altitude and you can hit obstacles if your altitude has drifted just couple of feet. Probably it could be used if backed by GPS as EGPWS does or non baro RNAV approaches do. But even GPS precision alone is ...


9

No, fiddling with your altimeter setting doesn't change the airspace you are flying in. So you can't bust the class A above 18 000 ft by changing the setting. The top and bottom boundaries of the airspace are defined by applying the altimeter setting local to that airspace. Conversely, and perhaps more important, you can't weasel out of a busted airspace ...


9

You're right that having a common transition altitude is better- efforts are underway in Europe to set a common transition altitude. Multiple studies have been carried out by Eurocontrol and it has been noted that it is better to have a single transition altitude. For example, from an aircrew prespective: The multiplicity of transition altitudes and the ...


9

There are a few types of altimeters but they all generally do the same thing and can be calibrated to anything if need be. Where they measure from and what they consider 0 are really 2 different questions. A pressure altimeter reads from the pito-static port (many planes have more than one of these for redundancy) and they are generally located forward on ...


9

That is because most of the legacy altimeter setting barometers cannot handle such high pressures. Most of them, like the one pictured below has a range from 28 to 31 inches of mercury. Kollsman Altimeter Setting Indicator, image from analogweather.com From Aeronautical Information Manual: 7-2-4. High Barometric Pressure a. Cold, dry air masses may ...


8

TSO C10B Altimeter, Pressure Actuated, Sensitive Type uses SAE AS 392C to specify minimum requirements for a pressure altimeter. It specifies two "types" of pressure altimeters Type 1: Range 35,000 ft Type 2: Range 50,000 ft AS392C also provides the tolerances a pressure altimeter must meet from -1000 ft to 50,000 ft. TSO C106 Air Data Computer also ...


8

If the altimeter says the station pressure is 29.92" sea level, but I am at 3000', then the airplane still thinks it's at sea level when it comes to performance. Is that wrong? Although the station pressure may be reported as 29.92", that does not mean that a barometer there will show that as the current pressure. The reported value is the actual pressure, ...


8

QNH is the atmospheric pressure adjusted to sea level. So, a reported QNH of 29.92 means the pressure is 29.92 inHg at sea level, regardless of the reporting station's elevation. If you're on ground at 3,000' MSL, you can rotate the knob to display 0' altitude, the pressure reading then on the altimeter window will be QFE (Field Elevation). (Source) Real ...


8

Your question is quite not clear, you are challenging definitions and use of definitions, but you may start with a misunderstanding: QFE = pressure measured by an altimeter which is adjusted to ground level (it gives a height of 0 when the airplane is on the ground). Definitions To ensure clarity, QFE/QNH: are reference pressures, not altitudes are ...


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