Convert your field or indicated altitude and QNH into pressure altitude — the figure performance charts and density altitude both start from.
Enter the field or indicated altitude and the QNH. SkyStudy applies the standard altimetry rule (30 ft per hPa, or 1000 ft per inHg) to give the pressure altitude you would read with 1013 / 29.92 set.
Enter an altitude and QNH to see the pressure altitude.
About 30 ft of altitude per hPa, or 1000 ft per inHg. Below 1013 / 29.92 the pressure altitude sits above your field elevation.
Feed the pressure altitude into the density altitude calculator with the OAT to see the altitude the aircraft actually performs at.
The 30 ft/hPa figure is the standard near-surface approximation taught for the ATPL. Use the aircraft altimetry system for primary reference.
Pressure altitude is your field or indicated altitude corrected for the difference between QNH and 1013.25 hPa. SkyStudy uses the standard 30 ft per hPa (1000 ft per inHg) altimetry rule.
Setting the standard 1013 / 29.92 in place of a lower QNH makes the altimeter read higher. Low pressure days give a pressure altitude above your field elevation.
It is the entry argument for performance charts and for density altitude. Almost every take-off, climb, and cruise performance table is indexed by pressure altitude.
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