GPS Approaches /Temperature compensation

[dhob]

I understand that, in the case of KGTF, LNAV/VNAV approach must not be performed if temp below -24°C. In my exemple, with temp -20°C, I can apply temp correction. Right?

First, Great Falls is not a CTA airport. Therefore CTA corrections are not required for any approach at any temperature. Second, the RNAV LNAV/VNAV approach is designed to clear all obstacles and terrain within the published temperature range.

Adding CTA corrections is not procedurally correct or necessary, and may induce errors if the FMC altitudes are not entered correctly. At a 121 airline, we have to comply with the published guidance.

EASA guidance is more explicit:
AMC2 CAT.OP.MPA.126 Performance-based navigation

Temperature compensation   
i For RNP APCH operations to LNAV/VNAV minima using Baro VNAV:   
A. the flight crew should not commence the approach when the aerodrome temperature is outside the promulgated aerodrome temperature limits for the procedure unless the area navigation system is equipped with approved temperature compensation for the final approach; 

B. when the temperature is within promulgated limits, the flight crew should not make compensation to the altitude at the FAF and DA/H;   

C. since only the final approach segment is protected by the promulgated aerodrome temperature limits, the flight crew should consider the effect of temperature on terrain and obstacle clearance in other phases of flight.