New tower approach calls
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Concur with the consensus here. QNH/QNE are the standards for baro altimeter settings. I’ve never seen QFE used, though it’s theoretically more useful in flat areas. Quite frankly, QFE is useless if you have a RADALT on board.
Of trivia, apparently QFE was once more widely used in the UK. We had a Kriegsmarine officer in my class in flight school who said the way they remember QFE was “Queen F***s Easy.”
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loooooooooooooooooool … yes my instructor back in France told me it was used by the old old pilots lol
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SL is Sea Level
AB, yes AirBase.
Ok if you’re fresh on this subject, it might be some mistaken from my understanding, thou still think not being clear enough…If you want to adjust altimeter to airbase altitudes pressure correction and assuming it’s not the tabled value… ex:
AB altitude is 980ft, but pressure is not at table values of 28,86’‘… so you need the new one, let’s say it’s 29,32’‘…
So you’ll need to adjust accordingly you altimeter for that, but you’ll need to adjust regarding Sea Level value which is the base reference, you will need to do the mentioned calculations in order to find SL new values… based on ATC (AB altitude) values.
29,92’’ (table SL value) - 28,86’’ (table 980ft value), then add this diff. to ATC’s value (29,32’‘)… resulting in corrected local AB, but at SL new value of 30,38’’
After doing calculations you’ll have a new SL value of 30,38’’ to adjust altimeter and not ATC’s value.
Am I wrong?All this looses meaning if ATC gives you QNH values at SL and not AB’s altitude… see?
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All ATC is based on an altimeter setting from MSL. When you get one from a tower it comes from their direct reading instrument. When you get it from anywhere else it comes from a certified weather reporting person and is what is used for the next one hour or if there is a rapid change they will put out a special report. Usually an aviation weather reporting station is within 100 to 150 miles apart and these altimeter settings are given by ATC enroute facilities. When aircraft climb to certain altitudes (each country establishes these base altitudes) then everyone goes to a standard altimeter setting. Here in North America that is 18,000 feet MSL which then becomes known as a “flight level”, Since all aircraft above 14,500 are contolled by ATC it simplifies communications. Also, ATC is then tasked with being responsible for altitude assignment when the mercury falls below 29.92 and FL180 becomes unusable. I spent 18 years as an air traffic controller an can usually explain what happens fairly well.
Lumper
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Oh crap, more European sh*t to relearn, we don’t use this QFE/QNE/QNH terminology in the US…
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Sure we do. We just say “Local Altimeter” and QNH is implied.
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@Home:
Sure we do. We just say “Local Altimeter” and QNH is implied.
Yea I know but we never say it… Now we have to say it in BMS…
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In real life if you get it wrong or forget, things like this could happen - if your into aerobatics of course:
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Flyway … here this is official document, from Canadian Transport Office.
1.5 pressure alTimeTer
1.5.1 General
The pressure altimeter used in aircraft is a relatively accurateinstrument for measuring flight level pressure but the altitudeinformation indicated by an altimeter, although technically“correct” as a measure of pressure, may differ greatly fromthe actual height of the aircraft above mean sea level orabove ground. In instances of aircraft flying high above theearth’s surface, knowledge of the actual distance between theaircraft and the earth’s surface is of little immediate value tothe pilot except, perhaps, when navigating by pressure patterntechniques. In instances of aircraft operating close to theground or above the highest obstacle en route, especially whenon instruments, knowledge of actual ground separation or ofApril 7, 2011
“error” in the altimeter indication, is of prime importance ifsuch separation is less than what would be assumed from theindicated altitude.
An aircraft altimeter which has the current altimeter settingapplied to the subscale should not have an error of more than±50 feet when compared on the ground against a knownaerodrome or runway elevation. If the error is more than±50 feet, the altimeter should be checked by maintenance asreferenced in AIR 1.5.2.
1.5.2 Calibration of the Pressure Altimeter
Pressure altimeters are calibrated to indicate the “true”altitude in the ICAO Standard Atmosphere. The maximumallowable tolerance is ±20 feet at sea level for a calibratedaltimeter. This tolerance increases with altitude.
The ICAO Standard Atmosphere conditions are:
(a) air is a perfectly dry gas;
(b) mean sea level pressure of 29.92 inches of mercury; mean sea level temperature of 15°C; and
(d) rate of decrease of temperature with height is 1.98°C per1 000 feet to the height at which the temperature becomes-56.5°C and then remains constant.
1.5.3 Incorrect Setting on the Subscaleof the Altimeter
Although altimeters are calibrated using the StandardAtmosphere sea level pressure of 29.92 inches of mercury, theactual sea level pressure varies hour to hour, and place to place.To enable the “zero” reference to be correctly set for sea level atany pressure within a range of 28.0 to 31.0 inches of mercury,altimeters incorporate a controllable device and subscale.Whether a pilot inadvertently sets an incorrect pressure on thealtimeter subscale or sets the correct pressure for one area andthen, without altering the setting, flies to an area where thepressure differs, the result is the same – the “zero” referenceto the altimeter will not be where it should be but will be“displaced” by an amount proportional to 1 000 feet indicatedaltitude per 1 inch of mercury that the subscale setting is inerror. As pressure decreases with altitude, a subscale settingthat is higher than it should be will “start” the altimeter at alower level, therefore, A TOO HIGH SUBSCALE SETTINGMEANS A TOO HIGH ALTIMETER READING, that is theaircraft would be at a level lower than the altimeter indicates;A TOO LOW SUBSCALE SETTING MEANS A TOO LOWALTIMETER READING, that is the aircraft would be at alevel higher than the altimeter indicates. As the first instanceis the more dangerous, an example follows:
A pilot at Airport A, 500 feet ASL, sets the altimeter to theairport’s altimeter setting of 29.80 inches of mercury prior todeparture for Airport B, 1 000 feet ASL, some 400 NM away.A flight altitude of 6 000 feet is selected for the westbound![](file:///page411image49400)
flight so as to clear a 4 800-foot mountain ridge lying acrosstrack about 40 NM from B. The pilot does not change thealtimeter subscale reading until he makes radio contactwith B when 25 NM out and receives an altimeter setting of29.20 inches of mercury. Ignoring other possible errors (seebelow), when the aircraft crossed the mountain ridge theactual ground clearance was only 600 feet, not 1 200 feetas expected by the pilot. This illustrates the importance ofhaving the altimeter setting of the nearest airport along theroute set on the instrument.
1.5.4 Non-Standard Temperatures-
(a) The only time that an altimeter will indicate the “true”altitude of an aircraft at all levels is when ICAO StandardAtmosphere conditions exist.
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(b) When the current altimeter setting of an airport is set onthe subscale of an altimeter, the only time a pilot can becertain that the altimeter indicates the “true” altitude iswhen the aircraft is on the ground at that airport.
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When 29.92 inches of mercury is set on the subscale of analtimeter within the Standard Pressure Setting Region, thealtimeter will indicate “true” altitude if ICAO StandardAtmosphere conditions exist or if the aircraft is flying atthat particular level for which 29.92 inches of mercurywould be the altimeter setting.
In general, it can be assumed that the altitude indication ofan altimeter is always in error due to temperature when anaircraft is in flight.
The amount of error will be approximately 4% of the indicatedaltitude for every 11°C that the average temperature of the aircolumn between the aircraft and the “ground” differs fromthe average temperature of the Standard Atmosphere for thesame air column. In practice, the average temperature of theair column is not known and “true” altitude is arrived at fromknowledge of the outside air temperature (OAT) at flightlevel and use of a computer. The “true” altitude found by thismethod will be reasonably accurate when the actual lapse rateis, or is near, that of the Standard Atmosphere, i.e., 2°C per1 000 feet. During the winter when “strong” inversions in thelower levels are likely and altimeters “habitually” over-read,in any situation where ground separation is marginal, a pilotwould be well advised to increase the altimeter error foundusing flight level temperature by 50%. Consider the aircraftin the above example; assume that the OAT at flight level inthe vicinity of the mountain ridge was -20°C; what was thelikely “true” altitude of the aircraft over the mountain ridge?
To calculate “true” altitude using a computer, the pressurealtitude is required. In this case, the altimeter indicates6 000 feet with 29.80 inches of mercury set on the subscale,therefore, if the pilot altered the subscale to 29.92 inches ofmercury momentarily, the pilot would read a pressure altitudeof 6 120 feet. Although the indicated altitude is 6 000 feet,if the altimeter setting of the nearest airport (B) was set, theTC AIM
indicated altitude would be 5 400 feet. With 29.20 inches ofmercury set on the altimeter subscale if the aircraft was on theground at B, the altimeter would indicate the “true” altitudeof 1 000 feet; assuming no pressure difference, it can betaken that the altimeter set to 29.20 inches of mercury wouldindicate the 1 000-foot level at the mountain with no error dueto temperature, therefore temperature error will occur onlybetween the 1 000-foot level and the 5 400-foot level, i.e.,4 400 feet of airspace.
(a) Set pressure altitude, 6 120 feet, against OAT, -20°C, inthe appropriate computer window.
(b) Opposite 4 400 feet (44) on the inner scale read 4 020 feet(40.2) on the outer scale.
Add the 1 000 feet previously deducted as being errorlessand find the “true” altitude of 4 020 feet + 1 000 feet =5 020 feet ASL. The margin of safety is now just over200 feet, but this does not take into account variableswhich may prevail as outlined immediately above and dueto mountain effect as explained below.
1.5.5 Standard Pressure Region
When flying within this region, the altimeter must be reset,momentarily, to the altimeter setting of the nearest airportalong the route to obtain indicated altitude, or indicatedaltitude calculated from the altimeter setting, and the stepsgiven above followed, or, when over large expanses of wateror barren lands where there are no airports, the forecastmean sea level pressure for the time and place must be usedto get indicated altitude. In the other instance, “airport” levelwould be zero, therefore subtraction and addition of airportelevation would not be done. The “true” altitude determinedin such a case would be “true” only if the forecast pressureused approximates the actual sea level pressure. (If sea levelpressure is not known and pressure altitude is used also asindicated altitude, the resultant “true” altitude will be the“true” altitude above the 29.92 level, wherever it may be inrelation to actual mean sea level).
1.5.6 Effect of Mountains
Winds which are deflected around large single mountainpeaks or through the valleys of mountain ranges tend toincrease speed which results in a local decrease in pressure(Bernoulli’s Principle). A pressure altimeter within such anairflow would be subject to an increased error in altitudeindication by reason of this decrease in pressure. This errorwill be present until the airflow returns to “normal” speedsome distance away from the mountain or mountain range.
Winds blowing over a mountain range at speeds in excessof about 50 KT and in a direction perpendicular (within30°) to the main axis of the mountain range often create thephenomena known as “Mountain” or “Standing Wave”. Theeffect of a mountain wave often extends as far as 100 NMdownwind of the mountains and to altitudes many times higher than the mountain elevation. Although most likelyto occur in the vicinity of high mountain ranges such as theRockies, mountain waves have occurred in the Appalachians,elevation about 4 500 feet ASL (the height of the ridge ofour example).
Aware and the Air Command Weather Manual (TP 9352E)cover the mountain wave phenomena in some detail; however,aspects directly affecting aircraft “altitude” follow.
1.5.7 Downdraft and Turbulence
Downdrafts are most severe near a mountain and at aboutthe same height as the top of the summit. These downdraftsmay reach an intensity of about 83 ft. per second (5 000 ft. perminute) to the lee of high mountain ranges, such as theRockies. Although mountain waves often generate severeturbulence, at times flight through waves may be remarkably“smooth” even when the intensity of downdrafts and updraftsis considerable. As these smooth conditions may occur atnight, or when an overcast exists, or when no distinctive cloudhas formed, the danger to aircraft is enhanced by the lack ofwarning of the unusual flight conditions.
Consider the circumstances of an aircraft flying parallel to amountain ridge on the downwind side and entering a smoothdowndraft. Although the aircraft starts descending becauseof the downdraft, as a result of the local drop in pressureassociated with the wave, both the rate of climb indicatorand the altimeter will not indicate a descent until the aircraftactually descends through a layer equal to the altimeter errorcaused by the mountain wave, and, in fact, both instrumentsmay actually indicate a “climb” for part of this descent;thus the fact that the aircraft is in a downdraft may not berecognized until after the aircraft passes through the originalflight pressure level which, in the downdraft, is closer to theground than previous to entering the wave.
1.5.8 Pressure Drop
The “drop” in pressure associated with the increase inwind speeds extends throughout the mountain wave, thatis downwind and to “heights” well above the mountains.Isolating the altimeter error caused solely by the mountainwave from error caused by non-standard temperatures wouldbe of little value to a pilot. Of main importance is that thecombination of mountain waves and non-standard temperaturemay result IN AN ALTIMETER OVERREADING BY ASMUCH AS 3 000 FT. If the aircraft in our example had beenflying upwind on a windy day, the actual ground separationon passing over the crest of the ridge may well have been verysmall.
1.5.9 Abnormally High Altimeter Settings
Cold dry air masses can produce barometric pressures inexcess of 31.00 in. of mercury. Because barometric readingsof 31.00 in. of mercury or higher rarely occur, most standardaltimeters do not permit setting of barometric pressures aboveApril 7, 2011
that level and are not calibrated to indicate accurate aircraftaltitude above 31.00 in. of mercury. As a result, most aircraftaltimeters cannot be set to provide accurate altitude readoutsto the pilot in these situations.
When aircraft operate in areas where the altimeter setting isin excess of 31.00 in. of mercury and the aircraft altimetercannot be set above 31.00 in. of mercury, the true altitude ofthe aircraft will be HIGHER than the indicated altitude.
Procedures for conducting flight operations in areas ofabnormally high altimeter settings are detailed in RAC 12.12.After reading this … i think you will understand that you are doing something wrong.
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In RL, When tower gives you the current local altimeter setting, it is up to date b/c they (the tower) has a barometer readout right there. It is the most accurate. The only time you make certain manual corrections is when the temperature is very cold (below 0 degrees).
The creator of the altimeter (cant remember his name atm) once said something that made a lot of sense… “It is only when you understand that this instrument (the altimeter) is a device for measuring pressure, and not altitude, that you will truley understand its capabilities and limitations…”
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Hi guys, i think i can help here.
QNH is used when you want to adjust your altimeter to a pressure level.
If you take your Airport diagram\ chart, you will see that there a field elevation. Field elevation is in relation to the the sea level. If your chart says the field elevation is 980 ft …you are actually at 980 feet above sea level. This makes sense, since you can’t be at 980 ft above ground …while being on the ground …lool.
Now with the QNH, if on your Altimeter you put in the right altimeter setting you will have 980 feet indicated on your altimeter. Which corresponds to your altimeter setting.
Now when you are flying, when you get above 18 000 ft … your altitude is no longer reported as altitude but as Flight Level. FL 200 corresponds to 20 000 ft.
When you fly above 18 000 ft , you change your altimeter setting to 29.92 … why ?
Because 29.92 has been stated as being the pressure in the standard atmosphere, which says that at Sea Level in the standard atmosphere the pressure is of 29,92 Hg and the temperature is 15 degrees Celsius and the air cools down at 2degrees Celsius per 1000 ft.
Thing you have to remember is that whatever QNH you give in, it gives you your height above sea level and not ground !! this is why when you select Radar altimeter to be indicated on your HUD you will have a difference.
Now, why do we set an altimeter setting ? because the standard atmosphere that is used as a reference … almost never exists. It is very rare actually that it will be 15 celsius at sea level with a pressure of 29.92.
Talking about pressure i mean here the force exerted by a column of air, this gives you the pressure that the air exercess above the ground or the altitude at which you are.
Cold Air is denser than Warm air. For a same quantity of Air, Cold air is heavier than warm air, it also means that cold air exercise more pressure than warm air.
This also means that the pressure of the air that you are going to have in warm air at 10 000 feet is not the same as the one you are going to have in cold air at 10 000 ft.
This means that for two different air Masses … 10 000ft is not equal to the same QNH on your altimeter.
This is why you have to reset altimeter setting, before takeoff, during navigation below 18 000 ft, during descent\before landing …to make sure we are not too low or too high.
Remember, above 18 000 ft, everybody has to set 29.92 as the QNH on his altimeter. You are going to tell me that it is not correct, but … since everybody flies with the exact same “error” … we are safe.
So again QNH = height above Sea level known as ASL.
NOw the QFE … if you set that in in your altimeter … it will indicate your altitude above the airport, so on the ground you will be at 0ft. But it is only useful for the airport …for landing or taking of, and it only gives you your altitude above the airport …not above the surrounding terrain … like mountains. Because if you set in the QFE …and fly towards a mountain …even if you fly very low above it … it will never get near to 0 ft …this is again not your altitude above Ground, but above airport only … and this is also why it is almost not used anymore.
I myself never used QFE, but it depends from the countries you fly in. In France they do not use it anymore, they do use QNH.
QNH is in Hg … and QNE is the same but in hPa ( hectopascals) and since 1 hPa = 1 millibar …you cans say both.
And 29.92 Hg is equivalent to 1013.2 hPa.
In Northern America we use Hg and in Europe they do use hPa. …
So to resume it all:
QNH/QNE is the pressure level at which you fly that gives you an altitude. QNH/QNE varies with the Weather, ( low pressure, high pressure ).
QFE … is not used anymore in the cicvil …don’t know about the military, but i don’t think so …because it is only useful above the airport.
I can get more in details if you want, but for Falcon this will be enough i think .
You were very instructive my friend! Thanks for the info!
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Sorry for very noob question: how it is possible to show up the second Tower page? T+T doesn’t run in my case.
Thanks
G. -
Hi gancio
Probably you imported the old config files and or stick profiles (OF ??).
Check your ini settings is there what you miss.
Try to use a differnt key settings and you will see back the second T page.
Cheers -
Thanks for quick reply.
Yes I’ve loaded my old key config to let my cockpit run.
Oh oh I must to rewrite everything….
Many thanks.
Giorgio -
Bumping an old thread just to clear up something that I think I understand. Could you check my statements below and tell me if I’ve understood it correctly?
Regional QNH is what you should be using below transition level, ie 14000’. This is known as “Altimeter” setting. So, I get cleared above 14000’ and altitude is then reported as Flight Level. Once above 14000’, do I then set my Altimeter to the Standard (which I understand as a sort of Global average pressure at sea level) of 1013mbar?
Am I right in saying that this is not the same as Force QNH? Force QNH is what you’d use when below transition level but over airspace where you can’t get local QNH/Altimeter settings, such as over enemy territory?
I understand what QFE is, but why or when would that be used?
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Yep, above 14k in Korea go standard.
QFE is Field Elevation, basically the pressure at any given field will resolve to your altimeter reading zero when on the ground.
Force QNH? No idea Harry…
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Yep, above 14k in Korea go standard.
QFE is Field Elevation, basically the pressure at any given field will resolve to your altimeter reading zero when on the ground.
Force QNH? No idea Harry…
I remember being told that over enemy airspace, you obviously can’t radio a weather station/tower to get a local QNH so a force QNH was to be used. If I remember right, it was lowest regional QNH of the day.
This is a very old video, but I found this on YouTube and I know understand FL a lot better. It makes much more sense now. FL are fixed altitudes from a fixed ‘standard’ pressure of 1013.2mb. Only when you drop below the national transition level, do you start using local QNH values.
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Yep, force QNH is comparable to Regional QNH. Except with Regional you have the lowest QNH value for a FIR or smaller fixed aera and Force QNH is calculated from the same principle (lowest QNH) of some reporting stations for a specific area in which the force is going to operate.
The question is how do they get the different QNH since you can’t really predict pressure settings precisely, you must observe it.
Anyway, Regional QNH is more a civilian thing for a known area with cooperating reporting stations, Force QNH is the same over a dynamic area where a force is going to operate
Both case take the lowest QNH value observed in their own areaIn BMS we don"t really have regional QNH, we only use local QNH
We don’t have Force QNH either … yetSo basically for now, under the TL: local QNH and above the TA: 1013.2hPa or 29.92inHg
In BMS Korea TA and TL are equal: TA: 14000feet, TL:FL140
In some countries TL will be assigned by ATC depending on the delta Pressure from standardAnd here’s a trick to get QNH on the ground without asking ATC:
Check the chart, note the field elevation
Rotate the alt pressure setting on the altimeter until the altitude displays the fiel elevation and the setting in the pressure windows is the QNH
Do the same with 0000 on altimeter and the setting in the pressure window is the QFE -
I meant to add, QFE is also useful when you’re in trouble, for example in a flamed out jet running on emergency power. You’ll have no radar altimeter and knowing QFE for the field you’re going to attempt to land at, you can then use your altimeter readout to have a better idea when to flare on landing - you’ve enough on your plate without having to remember field elevations, etc.
See here -
When I crash down, the altimeter reads zero. Ignore the fact it went all to pot please…
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QFE is almost no more used in military aviation (except by the funking french and their bad habits ;)) … it has been proven as accident-prone.