[cynwoody]

Sounds like he may have flown too high too long for his respiratory capacity, and lost consciousness.

According to FlightAware, he was at 21,000 for about an hour, until 12:00 EDT, then took a little over half an hour to descend to 13,100, where he stayed more or less until beginning a descent shortly after 3pm. FlightAware's last altitude was 4,600 at 3:13, but their record doesn't end until 4:03.

According to the Wikipedia, the service ceiling of the SR22 is only 17,500 ft.

[editor-surveyor]

Maybe the descent was not intentional?

We’ll probably never know.