Density Altitude=Pressure Alt +/- 120T, where 'T' is the ISA deviation.
i.e. : if PA is 13000' and SAT is -31 C, ISA deviation is, therefore, -20. DA is 13000-(120 x 20) =11600'. Easy, innit?
Okay, spot the deliberate mistake (please see below) <img src="rolleyes.gif" border="0">
[ 21 January 2002: Message edited by: fokker ]</p>