Hi spinrecovery,

If you zero the altimeter, the altimeter sub-scale will read the QFE which is the atmospheric pressure at your current position. The "FE" stands for "Field Elevation" so QFE is the code they used when querying the pressure at field elevation. QFE isn't used operationally in Australia any more. All operations will be on QNH or 1013 depending on your altitude.

Cheers,

Rich

So basically, to find the field elevation QFE just set the altimeter to zero and to find the QNH set the altimeter to airport elevation.

Yep that's it 🙂

...and to find your pressure height, simply set 1013 on the sub-scale.

Cheers,

Rich

Hey Richard

Could I please clarify, where you will read QFE from if you set zero on the altimeter?
Will the sub scale read elevation, or do you need to set zero on the sub scale to get the elevation from the altimeter?

Bec

Hi Bec,

An altimeter simply measures the difference between the pressure around you at the moment and the pressure you have set in the sub scale. This difference is then displayed in feet where 1 hPa of difference is shown as 30 ft of altitude difference. In other words, it shows you how many feet there are between the altimeter and the point in the atmosphere where the pressure is what you have set on the sub scale.

So, if we set 0 ft on the altimeter, the altimeter is simply saying "There are 0 ft between you and the pressure you set on the sub scale". If there are 0 ft between us and the sub scale, then the sub scale must be the pressure right here, right now. Therefore the sub scale is telling us our QFE.

Similarly, if we are at an airfield with an elevation of 1200 ft (for example) and we we wind the hands of the altimeter to show 1200 ft on the altimeter face, we can look at the sub scale reading and see the pressure at sea level. The altimeter in this case is saying "There are 1200ft between you and the pressure set on the subscale". If we are 1200 ft above the sea and the altimeter says we are 1200 ft above the pressure set on the subscale, then it follows that the pressure on the subscale must be the pressure at sea level at the moment. The sub scale setting would therefore be the current QNH.

Cheers,

Rich

Thanks Rich
That's helped a lot

Bec

🙂

So is field elevation a measure of height or pressure?
You said that the QFE will be displayed on the sub scale but I thought that only showed figures of pressure?

Elevations are surveyed heights above sea level. Altitudes are heights above some datum, typically sea level. QNH and QFE are pressures where QFE is the pressure at [b]F[/b]ield [b]E[/b]levation and the QNH is the pressure at [b]N[/b]il [b]H[/b]eight.

Cheers,

Rich

Thanks for clearing that up.
Is the altimetry section of the day vfr syllabus (3.6.5), referring to what we've been speaking about?

Yes, 3.6.5 (a) deals with these sub-scale settings.

[b]Area QNH[/b] comes from an area forecast and is the QNH setting for the defined region covered by the forecast. It is guaranteed to be within 5 hPa of any local QNH in the area.
[b]Local QNH[/b] is the actual QNH (sea level pressure) at the aerodrome. It may differ slightly from area QNH but will be pretty close. Local QNH is very accurate but applicable only to the local area of the aerodrome.
[b]QFE[/b] is the pressure at the aerodrome. With the aircraft parked and QFE set on the sub-scale, the altimeter will read 0 ft.
[b]Standard Pressure Setting[/b] is 1013 hPa set on the sub-scale and in this case the altimeter will read your Pressure Height. If an aircraft is going to be cruising above 10000 ft, it will need to set the Standard pressure Setting on the sub-scale and fly at defined "Flight Levels"

For more information on altimetry, check out this graphic from the old VFG: http://www.bobtait.com.au/vfg/#225/z

Cheers,

Rich

Great .
Thanks for your help.
I really appreciate it.

Bec