Altitude calculations

 We begin with the Altimeter setting, from AWOS eg:

Alt setting: 29.82
Field Elevation: 1051

29.92 is the 'standard' Altimeter

PA - Pressure Altitude is what you'd read on the altimeter in your plane if set to 29.92.  You can also calculate it:
(Standard Pressure - AWOS pressure) * 1000 + Field Elevation = PA
(29.92 - 29.82) * 1000 + 1051 = 100 + 1051 = 1151

PA: 1151
The PA assumes a lapse rate of 1.98 for the pressure from Field elevation to Sea.

Density Altitude - DA is PA adjusted for temperature

Most POH's use DA in their takeoff & landing calcs
        Density Altitude is the best predictor of aircraft performance

Solved on the E6B in the right window

This calc assumes dry air, moist air makes it lower!
        A: Use E6B with temp and PA - on right line the temp up with the PA, then read DA

Absolute Altitude - Exact height of airplane above terrain

Misc:

Station pressure - weight of column of air above a station (not including the weight from it to sea level)

Station pressure corrected to sea level pressure is known as altimeter setting.

Getting the pressure below the station has two methods, one uses the ISA standard temp / pressure, the other (MSL) uses the average of the past 12 hours temperature to calculate it.

Use the altimeter setting of a station within 100 miles preferably.

Indicated altitude: The ASL height you see on your altimeter once you have set the altimeter to the nearest altimeter setting.

When standard conditions exist pressure altitude, density altitude, indicated altitude, calibrated altitude and true altitude will all be the same.

True altitude

Exact height above sea level

Rule of thumb method of calc: (or use l side E6b)

4 ft * 1000 for each 1º of temperature varies from ISA (15º)

EG OAT (outside air temp) is 0º

ISA @ 5000 ft is 15º (sea level) - 10º (2º/1000) = 5º ISA @ 5000ft
0 - 5 = 5 degrees colder than ISA

5 (thousand) x 4 ft = 20 ft

20 feet x -5 = -100ft

Actual altitude = 5000 - 100 = 4900 ft

True altitude, use e6b:

    Pressure alt 12,000 ft

    Indicated/Calibrated 11,000

    Temp -30

    Station elevation 3,000 ft

    Soln:

        Match 12,000 ft with -30 left side e6b window

        Find 8,000 ft (11,000 - 3,000) on inner wheel which matches 7,350 on outer wheel

        Add station elevation, 3,000 + 7,350 = 10,350ft is true alt, 7,350 is Absolute altitude

Absolute altitude 

Exact height above terrain

Takeoff and landing performance data will typically be reported in the POH or AFM is according to density altitude.

The hotter the weather the greater the spacing in the altitude, so as it gets hotter than standard the airplane will indicate you're flying lower than you actually are, or indicated will be greater than true when temp >15º