The extreme cold weather lurking about got me thinking. The apparent default low temperature limit for electronic devices is -20 deg C, which isn't all that cold. So I looked into the stated limits for the various electronic devices in the plane. Of course, the limitation on the airplane itself is stated as -40 deg.
Txpdr (KT74): -25 deg C
KAP140: -45 deg C
GNS units: -20 deg C
VM1000: -50 deg C
Stratus 3: -20 deg C
Audio Panel: -20 deg C
There are a number of places in North America the last couple of days where outside temps are well below that -20 limit. Lucky for me, I don't live in one of those places
As an effect of cold weather, anyone else have their displays appear more dim/washed out in the cold? Whenever I fly at night after the plane has been sitting in cold weather for a while (15-30 F) my displays always look very washed out for a while, almost like they are fogged up from behind. They usually go back to normal within 20 mins of flight.
I flew at -30C last winter for several hours on the way back from Florida (to Canada). My main concern was the breather tube icing up but inspection immediately after landing revealed absolutely no ice whatsoever. That was a relief and I don't worry about that anymore.
I routinely fly in below -20C temperatures but the plane usually starts from a heated hangar. In any case, I have never had any issues with the cold and we don't take the air temperature into consideration when deciding whether to go fly or not.
I suspect the -20 C you see on all these devices isn't really based on any real limitation because it's so common. You see it for almost everything electronic, avionic-related or not. Because of this it lacks credibility. Once in operation, all these devices heat up, so as long as it's not absurdly cold (actual number undefined) once one starts up they're going to be warmer while operating. So temperature at altitude isn't likely to affect them, even if these numbers are valid.
The KT74 is interesting. The manual describes the display washing out in cold weather but that it has a heater circuit specifically to warm up the display when operating.
My 430W exhibits a bit of washing out in warm weather. Today it looked fine initially (unheated hangar, overnight low around 27 deg F). After flying awhile the display exhibited some of this washing out. Cabin heat on halfway, uninhibited cleat sunshine day, OAT around 7 deg C. 430W Contrast set on "auto".
But just because there are low limits (whether precisely valid or not) one wonders if in some circumstances, if the plane is left on a cold, windswept ramp overnight, if something or other just won't fire up, at least initially,
Yesterday was a typical winter inversion here. Minus 16 on the ground at 9am, -7 at 5500'.
I don't think twice about flying in the cold. There are lots of northern based aircraft that are parked outside in really cold temps and while people worry about engines, I have never heard about avionics being a problem. Even car electronic displays can be slow initially in cold weather, but they warm themselves up. An advantage of really cold air is that it holds virtually no moisture so the icing risk is nil. Usually the air is dead smooth and the engine performs really well, especially in a high pressure system. On my trip home yesterday with two people on board and 30 gallons, I was cruising at 145 at peak EGT, 9.2 gph. Awesome.
I think these low temperature limits are merely testing limits. "The freezer went to minus 20 so that's all we can say."
One more note: cold air is denser so check your tire pressure. You have to adjust the warm air pressure up a few pounds to have the correct pressures in cold air. There are tables online.
Yep, had a tire go off the rim in the turnoff to the taxiway after landing at -28C. Visual inspection in the heated hangar did not reveal abnormally low tire pressure,
