Originally Posted by
ve3id
Commercial chips are mostly designed and tested from 0 to 70 C. Industrial chips go to wider ranges, sometimes -40 to +105 C, sometimes more. Military/Aerospace spec are generally qualified from -55 to +125 C and are warehoused in a secure cage separately from commercial and industrial quality chips, with documentation attached to prove their having been tested. Complete systems are temperature cycled between the limits while cycling the power supply between its limits. I believe avionics uses mil/aerospace qual chips, therefore should not be a problem at -40. That's why avionics is so expensive.
On many biz jets, which do have the space for EE bays within the pressure vessel, the majority of the avionic boxes are located in compartments which are completely unheated and unpressurized in flight e.g. the Lear 45, in which the central avionics computer, air data computers, nav and com radios, transponders, attitude/heading computers etc. are all located in the nose, forward of the flight compartment. There is nothing between the avionics and the intense cold found at the flight levels but the thin metal skin of the two removable doors used to access the equipment on the ground.
A similar situation exists on a Hawker 800, where all sorts of avionics are crammed into a space in the upper portion of the nose gear wheel well. Again, this compartment is completely unheated and unpressurized, and is also exposed to wind blast and moisture anytime the nose gear is deployed.
The point being that the majority of commercial avionics systems are designed to operate perfectly well over a very broad range of environmental conditions, including prolonged exposure to extreme cold.