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In a flight performance graph what is the meaning of airport pressure altitude? Is it the top of climb? Because if I set my altimeter to 29.92 it will give me the pressure altitude for an airport at msl to be 0 feet, but in a performance graph I saw an airport pressure altitude to be 6000 feet.

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    $\begingroup$ Re " Cause if I set my altimeter to 29.92 it will give me the pressure altitude for an airport at msl to be 0 feet" -- this is not correct unless the airport is at sea level. $\endgroup$
    – quiet flyer
    Commented Mar 24, 2023 at 18:18

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Pressure altitude is the altitude you see on the altimeter when it is set to 29.92. If you take off out of Colorado Springs (6,187' FT MSL) and set 29.92 on the altimeter you won't see 0' on the altimeter, you will see something near 6,187' FT MSL

On the performance graphs, we convert the airport elevation and cruising altitude to pressure altitudes by applying the conversion between standard pressure (29.92) and actual pressure.

The formula is as follows:

  • 29.92 - [Airport reported altimeter setting]
  • Multiply result by 1,000
  • Add result to airport elevation or cruising altitude

For example. At Colorado Springs (6,187) and a current altimeter setting of 29.85.

  • 29.92 - 29.85 = 0.07
  • 0.07 x 1,000 = +70
  • 6,187 + 70 = 6,257 FT pressure altitude

If cruising at 10,000 FT, the resulting pressure altitude to be used in the performance charts would be 10,070 FT.

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  • $\begingroup$ Thanks .For the crusing altitude who decides ( atc or pilot) or is there a given range to pick from , and it's me how do I determine what altitude I should set ? $\endgroup$
    – Godsfavour Miracle
    Commented Mar 25, 2023 at 16:23
  • $\begingroup$ Under VFR, the pilot decides on a cruising altitude. Odd altitudes+500 going east and even altitudes+500 going west. You look at the performance charts to determine the altitude you want to cruise at. The higher you go, the faster the true airspeed and ground speed. Cruising altitude depends on distance, weather, fuel, passenger, etc. That is why you "get the big bucks" to make the best decision. $\endgroup$
    – wbeard52
    Commented Mar 25, 2023 at 16:36
  • $\begingroup$ Thanks and God bless you $\endgroup$
    – Godsfavour Miracle
    Commented Mar 25, 2023 at 18:37

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