Total T from OAT
Hi!!
You need also the velocity (or even better the Mach number). The total temperature (Kelvin) is:
Tt = OAT*(1+0.2*M*M)
where OAT is in kelvin and M (mach number) is = v/a. v is your TAS and the speed of sound a(in m/s)=sqrt(1.4*286*OAT(in kelvin)). If you were looking at the flight map in the pax cabin probably you did not have neither the wind, neither the Mach number, so as a first approximation you could use the displayed GS. You must use the same units for v and a (i.e. m/s).
Bye,
Marco