Okay, we seem to be a bit at logger heads here
The problem seems to be what the definition of density altitude is and how that then aerodynamically and performance related effects the aircraft.
Density altitude is pressure altitude corrected for variations in temperature. A definition, not mine :-
"Density altitude is defined as the pressure altitude corrected for non-standard temperature variations. And while this is a correct definition, my definition is perhaps more appropriate: DENSITY ALTITUDE IS THE ALTITUDE THE AIRPLANE THINKS IT IS AT, AND PERFORMS IN ACCORDANCE WITH."
If you look at any performance graph for a commercial aircraft you will find the pressure altitude, because thats what you read off of your calibrated altimeter corrected to msl by the pressure setting. This will then be cross coupled with ISA +10, ISA +20,ISA +30 temperature lines. You enter the graph for, say, single engine performance at your pressure altitude, for example 1000'. This would then be ICAO corrected at 1.98 degrees per 1000' therefore I would EXPECT the temperature to be 13 degrees. I look at my OAT guage and see the temperature is 33 degrees and, hey presto, I have ISA+20. Then I correlate my pressure altitude line to the ISA+20 altitude line to give me ..... my density altitude, which can then be applied to the performance figures for the engines to find my value.
I have operated helos all over the world including in hot & high environments and have ALWAYS calculated my performance figures based upon density altitude because performance on a 1013 day in england at 10 degrees OAT is not the same as the performance from the same helo in Dubai on a 1013 day at 45 degrees OAT even though the barometric pressure altitude is the same!!!
Pressure altitude is used as a base line because its given by the instrument, only the uncautious would use it without taking into account the OAT.
P.s. Just checked a couple of other aircraft types, and they are all Pressure corrected for temperature, i.e. density. S61N, S76, EC135
Your turn.......
