QNH and QFE
I just read about QNH and QFE so I thought I’d throw this out there. We don’t use QFE in the US but I think my logic is correct.
From the FAA Instrument Procedures Handbook
Barometric Pressure for Local Altimeter Setting (QNH)
A local altimeter setting equivalent to the barometric pressure measured at an airport altimeter datum and corrected to sea level pressure. At the airport altimeter datum, an altimeter set to QNH indicates airport elevation above mean sea level (MSL). Altimeters are set to QNH while operating at and below the transition altitude and below the transition level.
For flights in the vicinity of airports, express the vertical position of aircraft in terms of QNH or QFE at or below the transition altitude and in terms of QNE at or above the transition level. While passing through the transition layer, express vertical position in terms of FLs when ascending and in terms of altitudes when descending.
When an aircraft that receives a clearance as number one to land completes its approach using QFE, express the vertical position of the aircraft in terms of height above the airport elevation during that portion of its flight for which you may use QFE.
Note that transition level is when you set the altimeter to a standard value—QNE. It varies by country. In the US it is 18,000′ and 29.92 inches. Not relevant to this discussion.
In the US we don’t use QFE, but you would probably get that from the ATIS at the field where you are landing. If no ATIS is available, to convert QNH to QFE you would move the altimeter so that you decrease your altitude by the field elevation. Here’s an example:
My field elevation is 212′. If I set the altimeter to QNH it will show 212′ as the altitude. To get QFE I need to change the altitude to 0′. In other words whatever altitude is showing on the altimeter, move the knob to make it show 212′ less.
Note that when you turn the altimeter knob the altitude goes in the same direction as the pressure setting in the Kollsman window. In the US we use inches of mercury not millibars but the movement is the same: As an example, right now the altimeter setting at KSBP is 30.08. The setting at KSBA (62 nm away) is 30.01. If you fly to KSBA you would notice a change in altitude of -70 feet when you get the new altimeter setting from approach control.
If you ever wanted to see the inside of an altimeter, Paul Tocknel did too and took pictures as one was taken apart.
According to Wikipedia The abbreviation QNH originates from the days when voice modulated radio was often difficult to receive, and communication was done by Morse Code. To avoid the need for long Morse transmissions, many of the most commonly used communications were incorporated into a Q code. To ask for atmospheric pressure at sea-level (i.e., at zero altitude) the letters ‘QNH’ would be transmitted. A common mnemonic for QNH is “Query: Nautical Height”, whereas the mnemonic often used for QFE is “Query: Field Elevation”.
I don’t think I have ever seen the term QNE used, but the concept of transition level is one that anyone flying above 18,000′ knows. The Jeppesen approach charts show the transition level in feet and as a flight level (FL) as well as indicating whether the altimeter reading is in inches or hectopascals (hPa) but don’t mention that it is QNE.