I’ve been generally distrustful of my altitude preselect, as it seems to sometimes shoot on through the selected altitude. Today I had a calm flight to take a look at it, and there seems to be a problem.
It appears to be intermittently reading the wrong altitude, generally 400’ low. This causes it to climb right through selected altitudes. But then later, it will be indicating the correct altitude, and will climb/descend correctly. The Pressure Altitude indicated on the transponder is correct throughout this time, and ATC is getting the correct mode C altitude. Has anyone seen anything like this?