How can you determine the pressure altitude on an airport without a tower or FSS?

How can you determine the pressure altitude on an airport without a tower or FSS?

• A. Set the altimeter to 29.92 inHg and read the altitude indicated.
• B. Set the altimeter to the current altimeter setting of a station within 100 miles and correct this indicated altitude with local temperature.
• C. Use your computer and correct the field elevation for temperature.
• D. Set the altimeter to the airport elevation.

Answer: (A)

Pressure altitude is the altitude shown when the altimeter is set to the standard pressure 29.92 inHg. At an unattended airport, you don’t rely on local altimeter settings, so you determine pressure altitude by setting the altimeter to 29.92 and reading the indication. This reading represents the altitude in the standard atmosphere corresponding to the current pressure, independent of local weather or field elevation. Using a station’s current altimeter setting and correcting for temperature would yield an altitude that accounts for nonstandard pressure and temperature, i.e., true or density-altitude effects, not the pure pressure altitude you’re after. Correcting field elevation for temperature likewise gives density altitude, not pressure altitude. Setting the altimeter to the airport’s elevation simply shows the field elevation, not the pressure-altitude value.

Pressure altitude is the altitude shown when the altimeter is set to the standard pressure 29.92 inHg. At an unattended airport, you don’t rely on local altimeter settings, so you determine pressure altitude by setting the altimeter to 29.92 and reading the indication. This reading represents the altitude in the standard atmosphere corresponding to the current pressure, independent of local weather or field elevation.

Using a station’s current altimeter setting and correcting for temperature would yield an altitude that accounts for nonstandard pressure and temperature, i.e., true or density-altitude effects, not the pure pressure altitude you’re after. Correcting field elevation for temperature likewise gives density altitude, not pressure altitude. Setting the altimeter to the airport’s elevation simply shows the field elevation, not the pressure-altitude value.