A PC-12 Instructor reported that the owner pilot flying the aircraft inadvertently deleted an enroute fix as he rapidly manipulated the Honeywell Primus Apex system.

Narrative

I was providing pilot services; as an insurance requirement; for an owner-flown trip in a Pilatus PC-12E with the 4-panel Honeywell Primus Apex system. The owner was flying and I was handling the radio communications. After a few reroutes Center finally cleared us 'direct ABC direct XYZ direct destination'. The pilot-flying was incessantly playing with the glass cockpit controls. The cursor was bouncing between pages and menus at a high rate. I was trying to remain vigilant to the various changes occurring while still keeping an eye out for traffic and plan ahead for the arrival phase of our flight. Somewhere in this process the pilot-flying had deleted the ABC waypoint from the FMS so the autopilot dutifully headed direct to XYZ. I did not realize this until a few minutes later when the next Center Controller queried where we were headed. As we had not passed ABC he directed us to go direct to ABC then resume our cleared route. With all the things that can be reprogrammed on a 4-panel glass cockpit it is hard to keep total situational awareness when someone is playing with it in a rapid manner. Once we were reestablished on course we discussed ways to avoid unpleasant surprises in the future. The main point we discussed was to slow down and think about the result before depressing any buttons.