On April 2, 2022, at 1119 eastern daylight time, a Learjet Inc 45, N877W, was substantially damaged when it was involved in an accident at Morristown Municipal Airport (MMU), Morristown, New Jersey. The two airline transport pilots and two passengers sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Each crewmember provided written statements and their statements were consistent throughout. According to the captain, who was the pilot flying, the airplane was established on a visual approach for landing on runway 23. The reported wind was from 340° at 3 knots gusting to 16 knots. The quartering tailwind was computed “within limits,” the thrust reversers were deployed at touchdown, and the airplane turned “sharply to the right.” He reported that, “It felt unusual. Normal crosswind correction inputs made no difference, extreme inputs were made, and still no control was possible.” The airplane departed the right side of the runway and the entire wing structure separated from the main fuselage, which continued for about 100 ft before coming to rest upright. The crew shut down the airplane and exited the main cabin door along with one passenger, while the second passenger egressed the airplane by the emergency exit. Examination of flight track data and airport surveillance video revealed a normal approach profile and that the airplane crossed the runway threshold about 120 knots groundspeed. About 9 seconds into the landing roll, the airplane turned sharply to the right and departed the runway. The thrust reversers on each engine were deployed and their positions were approximately matched. The windsock in the foreground of the video was nearly parallel to the ground, indicating nearly a direct crosswind to the landing runway that would have been towards the airplane’s right side. The accident site was photographed and a cursory examination of the airplane was completed by a Federal Aviation Administration (FAA) aviation safety inspector. Examination of photographs revealed skid marks on the runway surface that led to the ground scars that marked the airplane’s runway excursion. The skid marks began about 1,200 ft beyond the approach end of runway 23 and arced to the airplane’s right about 560 ft before transitioning to tracks in the grass. The cockpit voice recorder (CVR) was retained and forwarded to the National Transportation Safety Board (NTSB) Recorders Laboratory in Washington, DC. A review of the summary and transcribed portions of the flight prepared by an NTSB Recorder Specialist revealed that the crew listened to the Automated Terminal Information Service (ATIS) at MMU and were aware of the wind speed, direction, and warnings of “low level windshear” and questioned why runway 23 was in used when the winds favored runway 05. The air traffic controller explained that, due to a runway closure at Newark International Airport (EWR), Newark, New Jersey, the use of runway 05 at MMU allowed for improved conflict resolution and traffic flow at EWR. The wreckage was recovered and examined at a recovery facility in Clayton, Delaware, by a team of airframe and powerplant specialists supervised by two NTSB aerospace engineers. Detailed descriptions of the examination, component removal, and component download are contained in the public docket. The engines were examined, and the digital electronic engine controls (DEECs) were downloaded. The data indicated that both engines were operating normally and responding to power lever inputs throughout the approach and landing. Electrical power was applied to the airplane and the primary flight and multi-function displays were downloaded. The yaw force sensors were tested at the manufacturer’s facility using their Acceptance Test Procedure (ATP). Both sensors functioned as designed; however, the copilot’s sensor “failed the Output Balance Error element (i.e., zero load), as the measured value was -0.2256% FSO out of specification” in tension and compression. The nosewheel steering rudder pedal systems and components were tested at the manufacturer’s facility and functioned as designed and no significant faults were found to be present in any of the components. The brake control unit (BCU) and four-wheel speed transducers were tested at the manufacturer’s facility. The BCU was tested to the manufacturer’s ATP with no faults noted. The data downloaded from the BCU did not include date/time stamps and could not be positively correlated with the accident landing. Each of the four wheel speed transducers were tested through two different protocols. Each transducer passed both tests with no faults found. The nose wheel steering electronic control unit and the spoiler control electronics unit were tested at the manufacturer’s facility. During the examinations, no faults were found present in either unit. According to the FAA Airplane Flying Handbook, page 9-9: The landing process should never be considered complete until the airplane decelerates to the normal taxi speed during the landing roll or has been brought to a complete stop when clear of the landing area. Accidents may occur as a result of pilots abandoning their vigilance and failing to maintain positive control after getting the airplane on the ground. A pilot should be alert for directional control difficulties immediately upon and after touchdown due to the ground friction on the wheels. Loss of directional control may lead to an aggravated, uncontrolled, tight turn on the ground, or a ground loop. The combination of centrifugal force acting on the center of gravity (CG) and ground friction of the main wheels resisting it during the ground loop may cause the airplane to tip or lean enough for the outside wingtip to contact the ground. This imposes a sideward force that could collapse the landing gear. The rudder serves the same purpose on the ground as it does in the air—it controls the yawing of the airplane. The effectiveness of the rudder is dependent on the airflow, which depends on the speed of the airplane. As the speed decreases and the nose-wheel has been lowered to the ground, the steerable nose provides more positive directional control.