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Altimeter readings from ATC

Pro Member Trainee
Brook Trainee

When an ATC Center gives you an altimeter reading, WHERE is the reading being taken and how is applicable to you at your position and altitude?

Are they reading the barometer where they sit, or can they give you an accurate reading for your altitude?

Pro Member First Officer
Traches First Officer

My understanding is that they are giving you the barometric pressure at sea level at your given location. They measure it at the airfield and adjust it based on the field elevation. All it does is gives a base point to ensure that everyone's altimeter is accurate!

Pro Member Chief Captain
99jolegg Chief Captain

Brook wrote:

When an ATC Center gives you an altimeter reading, WHERE is the reading being taken and how is applicable to you at your position and altitude?

Are they reading the barometer where they sit, or can they give you an accurate reading for your altitude?

They give you either QNH or QFE.

QNH is the airfield pressure reduced to sea level via ISA (International Standard Atmosphere) figures i.e. 1mb per 27ft. This gives the pilot their altitude above mean sea level

QFE is the airfield pressure. Therefore, when you select the QFE and start flying (from the same aerodrome) you will have a height above the airfield

As an aside, QFF is similar to QNH but it is aerodrome pressure reduced to sea level via the actual conditions rather than ISA conditions

QNE is (strictly speaking) a height that is read on the altimeter when landing with 1013.25mb set on the altimeter. A common misconception is that QNE = 1013.25mb = standard pressure but it's actually a height.

Does that make sense?

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Pro Member Chief Captain
Tailhook Chief Captain

Rolling Eyes

Pro Member Captain
Westernstyle Captain

Ok then Question

Pro Member Chief Captain
99jolegg Chief Captain

Tailhook wrote:

Rolling Eyes

There's some more info here: http://en.wikipedia.org/wiki/Atmospheric_pressure

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Pro Member Chief Captain
Tailhook Chief Captain
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