On March 2, 2016, about 0800 eastern standard time, a Beech 99A, N198WA, operated by Wiggins Airways Inc., was substantially damaged during approach to Knox County Regional Airport (RKD), Rockland, Maine, following an encounter with severe turbulence. The commercial pilot was not injured. Instrument meteorological conditions (IMC) prevailed, and an instrument flight rules flight plan was filed for the flight. The non-scheduled cargo flight was operated under the provisions of Title 14 Code of Federal Regulations Part 135, and originated from Manchester Airport (MHT), Manchester, New Hampshire, around 0730.The pilot stated that the flight was in IMC on descent for the instrument landing system approach to RKD when the airplane encountered an area of continuous light to moderate turbulence. About 2,000 feet mean sea level (msl), and an airspeed about 130 knots, the airplane encountered severe turbulence, and the pilot initiated a missed approach. She decided not to attempt another approach to RKD, and instead diverted to Bangor International Airport (BGR), Bangor, Maine. She stated that the airplane continued to experience light to moderate turbulence enroute to BGR. After landing and securing the airplane, she entered the severe turbulence encounter in the aircraft log book. Examination of the airplane by a Federal Aviation Administration inspector revealed that both wings exhibited skin deformation, and the fuselage side skins were wrinkled. Further examination by a local repair station revealed substantial damage to the right wing root between the fuselage and nacelle, just aft of main spar. The right wing root-to-fuselage fillet fairing was also damaged just aft of the main spar. There were several other areas noted with wrinkled skin on both wings. The pilot held an airline transport certificate with a rating for airplane single-engine land, multi-engine land, and instrument airplane. She also held a first class medical certificate, issued on March 15, 2016. Her last flight review was completed on November 24, 2015. At the time of the accident the pilot reported 3,600 total hours of flight experience, with 2,784 hours in the accident airplane make and model airplane. She had had accumulated 480 hours of flight experience in IMC, of which 295 hours were in the accident airplane make and model. The RKD weather observation at 0756 included wind from 150 degrees at 20 knots, gusting to 30 knots, visibility 4 statute miles in mist, ceiling overcast at 700 feet above ground level, temperature 8 degrees Celsius (C), dew point 7degrees C, and altimeter setting of 29.43 inches of mercury. Peak wind from 150 degrees at 34 knots was recorded at 0716, with pressure falling rapidly. The Terminal Aerodrome Forecast for RKD, valid at the time of the accident, predicted wind from the southeast at 22 knots with gusts to 37 knots, and the potential for low-level wind shear at 2,000 feet, with wind from 180 degrees at 45 knots. The National Weather Service issued multiple AIRMETs for the region, which advised of widespread IMC, moderate turbulence, and low-level wind shear. There were no pilot reports (PIREPs) or SIGMETs for severe turbulence in the area. The operator's policy and procedures manual stated that it was a general policy of the company to suspend operations over a route that subjected equipment to unacceptable turbulence.