Question about Altitude Reading

I understand there are different ways to measure altitude, including sea level, barometric pressure, etc. Is there an option on either the A30neo or the Cessna Citation Longitude to change the altitude readout from sea level to actual feet above the ground? I notice when I land, say, in Salt Lake City or Denver the altitude reading is not telling me how high I am above the ground, but how high I am above sea level. It is this changeable?


I don’t fly either of those, but don’t they have a radar altimeter? The Cessna 208 has that, and appears on the G1000 when you are close enough.

QNH is height above sea level

QFE is height above the field

Google is your friend, before landing at a airport do ensure you know what the elevation of the landing runway is, then you can set up your approach correctly.

The barometric pressure is used to set the altimeter.

29.92 inches or 1013 mb is standard air pressure and when the altimeter is set at this the readings are in flight levels.

You can set it your self by working it out.

I fly in Europe so I use HPA, so 1 HPA = 27ft. So you would look for the Airfield’s elevation divide that figure by 27 and then take the result off of the current QNH you have set on the Altimeter that will ensure you are now set to the QFE (Field Elevation).

The amount of HPA to subtract is also often included on the plates as well. Saves you doing the maths!

I’m not sure I’m understanding the question, or why you would care about your AGL level, except as it applies to not flying into the side of a mountain that you can’t see. That’s what minimum enroute altitudes are for (MEAs) that are published on every instrument chart that exists. There are other minimums, MOCA (min off course altitude), MVA (minimum vectoring altitude), and a host of others that as pilots we don’t even know or care about, as it’s ATC’s responsibility to keep us away from the side of mountains under IFR, and ours to do so with our eyes in VFR.

Radar altimeters are not accurate or reliable above 2,500’ AGL, which is why they’re only used for the approach phase, and even then only affect what your minimum descent altitude is during an instrument approach in the soup. And while some GPSs will give you that info, I ask again why you really care as a pilot? The only relevant thing is that you keep adequate ground clearance for your safety, and that of people on the ground, which is the purpose of the areas marked in yellow on your sectionals. Other than that, and sheer curiosity I suppose, it’s irrelevant.

A confused KevyKevTPA

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Its actually a really important thing IRL.

Here in the UK when entering a circuit at an Airfield that does not have a Tower and may only be covered by a FISO (Flight Information Safety Officer) or have no coverage at all, we need to know our height above the ground (AGL). The circuit information is normally given in AGL for the airfield so at my local airfield the Overhead is 2000ft AGL and the circuit height is 1000ft AGL. So inbound I will reset my Altimeter to QFE so that I know that when I report overhead I am actually at 2000ft AGL. If I had left my Altimeter on QNH I would actually be at 1500ft AGL in the overhead, so now I would only have 500ft separation from traffic in the circuit and could end up in a situation where I also have traffic above me by 500ft in the overhead.
A FISO if there is one available will only give you information, they will not give you instructions, so as always under VFR it is the pilots responsibility to remain free of conflict with other aircraft.
So if all aircraft coming in to that airfield have set the correct QFE on their Altimeter join the overhead at the correct height AGL descend on the dead side join the circuit at the correct height AGL it makes keeping separation much easier and safer for all.

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As a side issue but related, the late Formula 1 Racing Driver Graham Hill died along with members of his team when he crashed his Piper Aztec whilst on approach in bad weather.

All his ratings were out of date and whilst the findings of the investigation were inconclusive it was widely thought that he failed to set the altimeter correctly thus he thought he was higher than he actually was and undertook a controlled flight into the ground.