On November 12, 2018, about 1415 eastern standard time, a Gulfstream American (Aero Commander) 690C, N840JC, was substantially damaged when it was involved in an accident near Myrtle Beach, South Carolina. The commercial pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he was following radar vectors for the downwind leg of the traffic pattern to runway 36 at MYR. He turned onto final approach and was inside the outer marker when he encountered heavy turbulence. As he continued the approach, he described what he believed to be a microburst and the airplane started to descend rapidly. The pilot added full power in an attempt to climb, but the airplane continued to descend until it collided with the Atlantic Ocean 1 mile from the approach end of runway 36. A witness stated that the airplane looked "relatively low." He watched the airplane for about 10 seconds before it impacted the water about 150-300 ft from the shore. He stated that the airplane was not doing anything erratic and he could not remember if he heard the engines running. After impact, the forward portion of the fuselage which included the cockpit separated from the airplane. The witness swam out to the airplane and assisted the pilot to the shore. In addition to the fuselage damage, the airplane also sustained substantial damage to the left wing and right horizontal stabilizer. The 1456 weather recorded at MYR included overcast clouds at 500 ft above ground level (agl) and wind from 360° at 10 knots. The temperature was 13°C and the dew point was 13°C. The altimeter setting was 30.16 inches of mercury. Between 1356 and 1456, the visibility was restricted in some form, likely in rain and/or mist, but the weather phenomena were not reported. Precipitation accumulation was noted during this period in the remark section. It is unknown why the system did not report or why the tower observer did not record or augment the observation. Rain was later officially reported after 1550. The next closest official weather reporting station was about 12 miles northeast at Grand Strand Airport (CRE), North Myrtle Beach, South Carolina. The airport had an automated surface observation system (ASOS) augmented by tower personnel. At the time of the accident, wind was from 350° at 4 knots, visibility was 1 1/2 miles in moderate rain and mist, and the ceiling was overcast at 500 ft agl. The following figure shows the accident airplane’s flight track overlaid on base reflectivity radar imagery. The flight track showed the last radar target at 650 ft mean sea level near the accident site. Echoes of 5 to 15 dBZ extended over the flight track and accident site. No strong reflectivity echoes or gradients were noted over or in the vicinity of the accident site to indicate any thunderstorms and the radial velocity data did not detect any divergent couplets typically associated with microbursts. Figure -Base reflectivity image with flight track overlay The NAM sounding wind profile indicated a surface wind from the ENE at 7 knots with wind veering to the south and southwest above the frontal inversion with wind speeds increasing with height. The mean 18,000 ft wind was from 240° at 35 knots. At 2,000 ft, the wind was estimated from 120° at 30 knots. The sounding supported a high potential for moderate turbulence below 2,000 ft and low-level wind shear in the inversion layer.