Having spent a lot of my life troubleshooting electronic systems I have found that new equipment is more likely to fail than one in service for a while. The Legacy plane was on it's initial real flight after the maintenance test flight so the transponder had never been exposed to the colder temperatures at altitude for a duration of time so hopefully when it is repaired the next crew will see if the transponder duplicates it's failure again when exposed to the same environment. If it fails again we will know why it quit working, if it works it could be an intermittent problem and not conclusive. The transponder started working again when they descended into warmer air so hopefully someone will look at that possibility. I could be wrong but I hope someone looks into this as a probable cause of the transponder failing.