OAT Out of Calibration

[Jerry 5TJ]

I was coming north a few weeks ago from Southern California and I noticed that the old OAT, the one sticking through the windscreen, showed 0C while flying in the clouds.  There was visible rain beading on the windscreen, but no ice at all.  That's odd, I thot.

Just recently I put in a new Davtron M803 to replace the long-dead "8 day" clock.  The Davtron has a voltmeter(very nice) and an OAT with a remote probe along with the timers and clock.    

I found out why no ice formed at 0C on the old Scott OAT -- it was reading about 4 C too low.   Gee, it is only 45 years old.   Moral of the story is obvious -- these are old airplanes and their parts are getting tired.  Some parts are more tired than other.

A good OAT is critical when flying in clouds.    Suggest you check yours for accuracy and/or get another.