A medical emergency, perhaps hypoxia, looks to have claimed another pilot and aircraft.
Two months ago to the day, it was a Cirrus SR22.
Today is was a Mooney M20M Bravo, N400DE, powered by a turbocharged Lycoming TIO-540 and registered to N400DE LLC of Ada, Michigan.
Based on flight tracking information from FlightAware.com, the lone pilot had departed Grand Rapids, Michigan around 0840h central time this morning, headed north and levelled off at 25,000ft by 0912h. At about 0937h, the aircraft reversed course. Pilots must use full-time supplemental oxygen above 14,000ft.
At some point, the pilot also stopped communicating with air traffic control which prompted the North American Aerospace Defence Command (NORAD) to launch F-16 fighters which met up with the plane near Muncie, Indiana at 1030h to check out the situation.
NORAD says Mooney pilot, who had departed Grand Rapids on a post-maintenance flight, was "unresponsive". The fact that the plane was on a post-maintenance checkout flight may very well explain the course reversal and some erratic indications on the transponder return for altitude -- the aircraft could not have physically moved 11,000ft in less than one minute, as the FlightAware data suggests.
At approximately 1105h, the plane's speed decreased and it's altitude began to drop, likely indicating the selected fuel tank had run dry. It crashed near Winchester, Indiana at approximately 1140h, according to NORAD.