Preflight and Weather Briefing
Before the flight, the pilot obtained a preflight weather briefing that revealed marginal VFR and IFR conditions along his proposed route. The briefing included a precaution for thunderstorms. An IFR flight plan was filed, and the aircraft departed.
Inflight Developments
Later during the flight, the pilot was radioed information about a convective SIGMET that contained a line of thunderstorms reaching 45,000 ft across his route. The pilot stated that he wanted to continue on his route and would check back later.
Approximately 20 minutes after that communication, the pilot was warned that he was about to enter heavy precipitation and was offered an escape route. His last transmission was "OK FOUR ONE POP."
Loss of Contact and Wing Separation
A few minutes after that transmission, his transponder code was lost on radar. The aircraft was at 9,000 ft MSL and experienced inflight separation of both wings.