chevron, thanks for your reply.
bookworm,
I do understand the temperature problems that arise while using the altimeter and it's indications.
The problem which was presented to me, was quite specific about the conditions, i.e. flying an instrument approach down to the MDA.
"And any time you use a QNH at a level different from the level it was measured at, you may need to apply a temperature correction. In particular, in IAPs in cold conditions, the altimeter will overread so a correction for temperature is required at any altitude that is critical."
Reading your post, it sounds as if while the approach is being flown and let's say that the OAT is ISA -20ºC, the pilot has to calculate the actual MDA. Is this correct?
Regards,
TG