I've flown the airbus for two different airlines in the US. At both airlines, it is in the books that anything that isn't an approved pilot reset procedure is never, ever to be attempted when in the air. We actually have a reset table in the manuals that shows a limited amount of procedures that can be done.

In the past year, I had an instance where coming from Cancun, flying over the Gulf, we lost our ACARS connection. Minor problem, we actually have an approved reset procedure in the books. The airbus has two types of breakers, monitored and unmonitored. Monitored breakers will show up as an ECAM if they are tripped. As I go back to see the breaker for VHF3 (the radio that transmits the ACARS information) I see a breaker popped that has nothing to do with the reset procedure. Honestly speaking I have no idea what this breaker is for, says something about data recording. Now smart me thinks, the ACARS is out and this breaker is popped, it has to be associated. Smarter me remembers that if this isn't an approved procedure, I can't touch that breaker. Smartest me knows that a popped breaker should never be reset in the air.

We continue on to our destination, using alternate means of communication with the company and getting our performance data. Get on the ground and our gate is occupied we got some time to sit in the holding pad. I call maintenance, and mention I made an entry into the logbook about the popped breaker. With their approval I reset the breaker. The moment I do this, we get our ACARS back. Cool. What also happened was both of our FMGC's cleared out all saved information including whatever was left on our flight plan even though we've already entered the done phase of flight. If I reset that breaker in flight, its now my understanding I would have cleared out our entire flight plan over the Gulf of Mexico.

This is why we have procedures, this is why we have the training we do.