HISTORY OF FLIGHTOn December 3, 2019, about 0833 eastern standard time, a BAE 125 800A airplane, N469RJ, was substantially damaged when it was involved in an accident near Detroit, Michigan. The airline transport pilot and copilot were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 repositioning flight for a subsequent Part 135 flight. According to the pilot in command who was flying the accident airplane, the airplane departed the Willow Run Airport (YIP), near Detroit, Michigan, and the crew was conducting an instrument landing system (ILS) approach to runway 33 at the Coleman A. Young Municipal Airport (DET), near Detroit, Michigan. The airplane broke out of the clouds about 1,500 ft above ground level (AGL), and the airplane had picked up rime icing during the flight. The air traffic controller at YIP advised them of the icing conditions present and the pilot turned on the airplane’s TKS [Tecalemit-Kilfrost-Sheepbridge Stokes] weeping wing deicing system. The airplane did not have any airspeed oscillations during the approach, and the crew maintained 140 knots on approach. The flight's calculated Vref speed was 128 knots. The pilot reported that the right wing "dropped" and a stall occurred. He said that there was no shaker activation during the flight. Federal Aviation Administration (FAA) inspectors examined and documented the airplane that came to rest on the infield grass near the control tower. The airplane had ice on the leading edge of the left wing and ice was observed on the ground under the left wing. An outboard section of the right wing was bent upward. Each engine’s Digital Electronic Engine Controller (DEEC) unit were shipped to their manufacturer for an examination under NTSB supervision. The download of the incident recorded data and fault history data from both N1 DEECs was completed successfully. Review of the data revealed that both engines were rotating, operating, and responding to power lever inputs throughout the approach and accident sequence. The flying pilot’s accident report, in part, stated, “Although flight crew selected the correct Vref speed for the aircraft weight, they failed to add 10 kts for the ‘operation in icing conditions’ statement, per the aircraft checklist. Vref should have been calculated at 138 KIAS with a minimum approach speed of 148 KIAS.” The non-flying pilot stated the airplane had come to a full stop in the grass. At that point his arm touched the control column, and he could feel that the stick shaker was activated/shaking. He thought the control column was all the way back. About 0807, another BAE 125 800A airplane had landed at DET. The pilot of that airplane stated that he was in his own airplane on the ramp waiting for passengers and witnessed the accident airplane exiting runway 33 traveling through the grass and across the taxiway coming to rest in the grass past the taxiway. Before entering the clouds, the witness reported the TKS ice protection system, engine heat, and engine ignitions were turned on. The witness, in part, stated the ice detected light illuminated during the approach and after landing there was some minor ice on the wing leading edge. The small temperature probe had an umbrella shaped ice formation. The outboard ends of the horizontal stabilizer had ice formation on about the outer 9 inches of both horizontals." AIRCRAFT INFORMATIONThe airplane’s ice detection system was equipped with a rotary-cutter type ice detector, two warning annunciators and a left-wing inspection spotlight. The system will automatically detect the formation of ice after takeoff; however, manual selection of the detector is available for operation on the ground. A TKS fluid airframe anti-icing system is provided for the leading edges of the wings and the horizontal stabilizers. The system is controlled by a timer switch and a warning chime, which will sound when the system setting times out and switches off. Anti-icing fluid for the system is stored in a tank with a total capacity of 5.55 US gallons, which provides priming and protection for about 61 minutes. METEOROLOGICAL INFORMATIONA review of 29 pilot reports during the 7 hours surrounding the period indicated 23 reports of icing between 1,600 ft and 4,000 ft. Most of the reports indicated light rime type icing being encountered with moderate rime to mixed icing encounters the second highest number of reports. There was a strong aircraft type bias in the reports with the majority of the light icing intensity reports being made by air carrier aircraft, and all the moderate icing from turboprop, business to smaller regional jet aircraft. The reports of no icing were also most common with departing jet aircraft rapidly climbing though the clouds, versus aircraft on a gradual descent. The reports of moderate icing were noted between 0500 and 0945 or immediately surrounding the time of the accident, with the light intensity icing reports dominating after 0945. No urgent or severe icing PIREPs were reported during the period. Cloud bases were reported near 1,600 ft with cloud tops ranging from 3,800 to 4,000 ft. AIRPORT INFORMATIONThe airplane’s ice detection system was equipped with a rotary-cutter type ice detector, two warning annunciators and a left-wing inspection spotlight. The system will automatically detect the formation of ice after takeoff; however, manual selection of the detector is available for operation on the ground. A TKS fluid airframe anti-icing system is provided for the leading edges of the wings and the horizontal stabilizers. The system is controlled by a timer switch and a warning chime, which will sound when the system setting times out and switches off. Anti-icing fluid for the system is stored in a tank with a total capacity of 5.55 US gallons, which provides priming and protection for about 61 minutes. FLIGHT RECORDERSThe CVR was shipped to the NTSB Recorder Laboratory. A CVR Factual Report was produced. The report confirmed the facts of the accident pilots’ statements.