This was an otherwise-routine, night VFR mission, and a proficiency flight for the SIC, who was serving as pilot at the controls (PAC). At 2345 local time and after approximately three hours on station at 24,000 feet msl about 20 miles east of the airfield, the PIC, in the right seat and the pilot not flying (PNF), saw a two-to-three-foot-high vertical wall of thick gray smoke enter the cockpit between his right shoulder and the right cockpit window. The entire cockpit was engulfed in this smoke after approximately five to eight seconds. Neither pilot could see any visible reference outside or inside the cockpit. None of the flight instruments or navigation devices were visible.
The crewman in the rear of the cabin was standing at the time, adjusting some equipment, and noticed the smoke exiting the cockpit and beginning to fill the cabin. Upon seeing the smoke, he returned to his seat and donned his oxygen breathing system.
