“Density altitude is pressure altitude corrected for temperature”. That is how I’ve been taught how to calculate density altitude.
Lets take the following scenario:
– Field Elevation: 650′
– Temperature: 8°C
– Dewpoint: -2°C
– Altimeter setting: 30.05″ Hg
– ICAO Lapse Rate: 1.98°C / 1000′
I’ve calculated pressure altitude to be 520′.
To Calculate density altitude:
Pressure Altitude + ((Temperature – ICAO Standard Temp)x100)
ICAO Standard Temperature in this case for the density altitude of 520′ would be (15°C – (520*0.00198)) or 13.97°C… Therefore:
520 + ((8 – 13.97)x100)) = -77′
Now, according to my Electronic E6B I get a density altitude of -204′. According to this online density altitude calculator it’s -276′ (I used 520 as the altitude value).
So who’s right? Air density is affected by water vapour content, so shouldn’t the density altitude formula include some value with the dew point? The online calculator I used asked for the dew point. Even if the ICAO standard temperature and pressure involve 0% humidity why is my E6B so off (or my calculations)?
Let me know what your thoughts are. If you spot a mistake in my calculations, let me know.