Figure: QNE vs. QHN vs. QFE, from Eddie's notes.
How you set your altimeter is not standard across the world but how you grew up is pretty much the way most of the world does it and is the ICAO standard.
How can things be different? Let me count the ways:
The ICAO reference documents are remarkably silent on the subject of metric and QFE altimeter operations, other than to say they are possible. Even the document devoted to summarizing differences, ICAO Doc 7030, fails to cover either subject. We are left to explore both subjects with hard-earned experience. It is a subject that can kill you.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue. A lot of this is just experience, as given in blue.
Does tech make all this easier? Sure. Fool proof? No, see Eddie Answers an Altimeter Question.
The definitions are clear but the source material is not. For a look at the definitions with the source material, see Altimetry / Altimeter Settings.
“Field Elevation” - Based on setting a locally provided altimeter setting which is determined by adjusting an altimeter on the ground until it reads zero. QFE allows us to read height above the runway.
“Height” - Based on setting a locally provided altimeter setting which is determined by adjusting an altimeter on the ground until it reads the station's correct elevation above the sea level reference datum. QNH allows us to read field elevation on landing.
“En Route” - Based on setting 29.92” or 1013.2 hPa, gives height above a theoretical datum which is not adjusted for atmospheric conditions. QNE provides the basis for flight levels.
[ICAO Document 4444, Ch 1] The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes.
[ICAO Document 4444, Ch 1] The airspace between the transition altitude and the transition level.
[ICAO Document 4444, Ch 1] The lowest flight level available for use above the transition altitude.
The key takeaway here is the transition altitude expresses the highest possible altitude, above that they don't exist. So when you are climbing, once you've past the transition altitude, they no longer exist so you might as well go to 29.92/1013. When you are descending, the lowest possible flight level is at the Transition Level and once you have past it, you might as well go back to QNH. Confused? Yeah, me too. More on this: Transition Altitude / Layer / Level.
In North America we tend to think of 18,000 feet and FL 180 interchangeably, they are where we switch from QNH to QNE going up, and QNE to QNH going down. We don't speak of transition levels and altitudes, instead the Aeronautical Information Manual, ¶7-2-1 speaks of lowest usable flight levels, which is a way of incorporating a transition layer.
Figure: Altimetry Chart Differences, from Eddie's notes.
The Jeppesen Airway Manuals do not explain charting differences and in some cases the differences are not consistent. You are left to compare one chart with another and look for someone with recent experience to determine what procedures are really being used at a particular airport. You can learn a few things by comparing three types of charts, and from that draw three conclusions:
The number of airports using QFE or metric has declined dramatically over the last two decades but you need to be cautious when flying anywhere that used to be a associated with the former USSR. It pays to talk to a pilot with recent experience.
Figure: Example ICAO Standard Approach Chart, from Jeppesen Airway Manual, Singapore ILS DME Rwy 02L, WSSS, page 11-1, 25 Nov 11, with Eddie's notes.
[ICAO Document 4444, §4.10]
126.96.36.199 For flights in the vicinity of aerodromes and within terminal control areas the vertical position of aircraft shall, except as provided for in 188.8.131.52, be expressed in terms of altitudes at or below the transition altitude and in terms of flight levels at or above the transition level. While passing through the transition layer, vertical position shall be expressed in terms of flight levels when climbing and in terms of altitudes when descending.
184.108.40.206 When an aircraft which has been given clearance to land is completing its approach using atmospheric pressure at aerodrome elevation (QFE), the vertical position of the aircraft shall be expressed in terms of height above aerodrome elevation during that portion of its flight for which QFE may be used, except that it shall be expressed in terms of height above runway threshold elevation:
220.127.116.11 For flights en route the vertical position of aircraft shall be expressed in terms of:
except where, on the basis of regional air navigation agreements, a transition altitude has been established for a specified area, in which case the provisions of 18.104.22.168 shall apply.
These ICAO procedures are almost universally used. There are exceptions by country (e.g., North Korea) and within countries (e.g., China). You must check the applicable AIP or Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures to be sure.
Chart Identification is left up to you, but as a general rule if the chart says "Alt Set: hPa" and there are no metric conversion tables, you are probably dealing with an ICAO standard chart requiring you to fly altitudes in feet and the altimeter set to QNH.
Figure: Example Metric/QNH Approach Chart, from Jeppesen Airway Manual, Beijing ILS DME Rwy 18R, ZBAA, page 11-5, 25 Jan 13, with Eddie's notes.
Chart Identification is left up to you, but as a general rule if the chart says "Alt Set: hPa" you will set your altimeter to Hectopascals, if the heights outside the parentheses are bolded you will be flying QNH, and if the chart has feet to meter conversion tables, you can expect to be vectored in meters.
Figure: Example Metric/QFE Approach Chart, from Jeppesen Airway Manual, Moscow Sheremetyevo ILS or PAR Rwy 07L, UUEE, page 21-1, 1 Nov 13, with Eddie's notes.
Chart Identification is left up to you, but as a general rule if the chart says "Alt Set: MM" you will set your altimeter to millimeters, if the heights inside the parentheses are bolded you are probably dealing with a QFE chart, and the presence of feet-to-meters tables means you will be vectored with altitudes in meters.
Figure: Example Hybrid Approach Chart, from Jeppesen Airway Manual, Sanyi ILS DME Rwy 02, ZPLJ, page 11-1, 27 Dec 13, with Eddie's notes.
Some countries have additional procedures at airports where no transition levels/layers are provided or where the elevation makes setting QFE impossible. Some countries have several procedures within their own borders, China for example:
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, China, Rules and Procedures, 11 Oct 2013] At aerodromes of high elevation: When the aircraft altimeter subscale cannot be set to the atmospheric pressure at the aerodrome elevation, it will then be set to 1013.2hPa before take-off, with the indicated altitude interpreted as zero altitude. When the aircraft altimeter subscale cannot be set to the atmospheric pressure at the aerodrome elevation, landing is to be made with the assumed zero altitude notified by the air traffic controller before landing.
I think this approach used to be QFE and required you to use an altimeter setting with an altitude pad provided by the tower, since you would not be able make your altimeter read zero on the ground at such a high elevation. Tower would give you an altimeter setting and tell you that runway elevation will indicate, for example, 2000 meters on touchdown. It appears most of these high elevation airports, like this one, have converted to QNH. But the high altitude note still appears in the ATC pages.
Figure: Old USSR Approach, from Jeppesen Airway Manual, Yerevan Cat II ILS Rwy 09, UBBB, Page 11-1A, 14 Feb 92]
My first approach into the old Soviet Union was this one, which looks more complicated than it really is. But back then, with no GPS and FMS to help us, it was a handful. These days as the aircraft get smarter they seem to be cramming more and more stuff on the approach plate which makes it that much more important to study the chart and figure out what you need to know when all the electrons go on strike.
Portions of this page can be found in the book International Flight Operations, Part VIII, Chapter 4.
ICAO Doc 4444 - Air Traffic Management, Fourteenth Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, 2001 *
ICAO Doc 4444 - Air Traffic Management, Fifteenth Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, 2007 *
* Not all of Doc 4444 seems to have been reproduced in the 15th edition, so you might need to look at the 15th edition and then then 14th edition for some sections.
ICAO Doc 4444 - Amendment No. 1, Procedures for Air Navigation Services, International Civil Aviation Organization, Amendment No. 1, 2007
ICAO Doc 4444 - Amendment No. 2, Procedures for Air Navigation Services, International Civil Aviation Organization, Amendment No. 2, 19/11/09
ICAO Doc 8168 - Aircraft Operations - Vol I - Flight Procedures, Procedures for Air Navigation Services, International Civil Aviation Organization, 2006
Jeppesen Airway Manual