Sudden Altimeter Change
I remember years ago descending into CDG around 15,000 ft in a 737, when both altimeters suddenly ran down to zero and then back to the correct altitude within about 2-3 seconds. Unfortunately during this apparent descent the autopilot “captured the cleared descent altitude” we had preset (somewhere around 6,000 ft) … and then once we were “back at 15,000 ft” the started a rather aggressive dive back down towards the captured altitude, which I was only able to stop quickly by disconnecting the automatics … before resetting various (altitude & modes) and re-engaging autopilot & A/T.
Then had the same thing happen about 2 weeks later.
Although ASR’d at the time I don’t remember ever getting to the bottom of what caused it although my suspicion has always been that it had something to do with mobile phones being turned on (give away “nya-nya-nya” chirp radio interference around the same time).