On November 11, 2023, about 1241 central standard time, an experimental amateur-built Lancair IVP Turbine airplane, N751HP, sustained substantial damage when it was involved in an accident near McKinney, Texas. The pilot and passenger were not injured, and an occupant in an automobile sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, while at FL 250 west of Abilene, Texas, the cockpit door seal failed, and the airplane sustained a sudden loss of pressurization. The pilot contacted air traffic control for an immediate descent. The pilot descended the airplane to 10,000 ft msl and continued the flight to Aero Country Airport (T31), McKinney, Texas. Following the emergency descent, the pilot noted no aircraft systems anomalies. About 5 minutes after establishing cruise flight at 10,000 ft to T31, the pilot noted an amber caution light for the propeller rpm which was indicating 1,920 rpm. The pilot reduced the propeller rpm to 1,800 and the caution light turned off. The pilot continued the flight to T31. The pilot reported he had not previously landed at T31 and performed a touch and go landing on runway 17 “to see the field.” The pilot climbed the airplane to the traffic pattern altitude and flew a normal traffic pattern to land on runway 17. During the downwind leg, the pilot pulled back the power lever and the ball on top of the lever (see Figure 1) came off in his hand. The pilot handed the ball to the passenger and continued the landing at the flight idle power position. Figure 1. Cockpit power lever and ball. The pilot stated the airplane touched down in the first 500 ft of the runway without a float or a bounce in ground effect; he immediately “hit [the] brakes gently” and maintained the runway centerline. For about 5 to 10 seconds, the pilot unsuccessfully attempted to move the power lever into beta-reverse. The pilot applied maximum braking; however, the brakes faded, and the stopping power decreased. The airplane exited the end of the runway, went through an airport perimeter fence, and struck a moving vehicle on a roadway. The airplane sustained substantial damage to the fuselage and right wing. ADS-B and avionics data showed the airplane’s groundspeed was between 96 and 99 knots and the flaps were extended to 40° during the final approach. A witness, located on a general aviation ramp on the east side of T31, video recorded the airplane’s landing on his cellular telephone. The video showed the airplane touch down, bounce, and touch down again near the midpoint of the 3,002 ft asphalt runway and evidence of braking action (smoke from main landing gear wheels/tires) occurred about 3 seconds later. The wheel/tire smoke continued until the airplane exited the runway surface. According to the T31 airport manager who examined the runway surface after the accident, the first visible tire skid marks were about 200 ft past the midpoint of the runway. The skid marks remained visible for about 1,300 ft until the airplane departed the end of the asphalt surface. The airplane continued 14 ft to the perimeter fence and then traveled 93 ft to the spot where it collided with a moving automobile in the roadway. Postaccident examination of the airplane revealed cable continuity from the cockpit power lever to the propeller governor. The cockpit control lever, without the ball top, was actuated between full power and the reverse positions with no anomalies noted. The cockpit door seal was intact, and no damage was noted to the seal adhesive or materials. A review of the aircraft maintenance records revealed that on March 29, 2022, the original Hayes IVP Turbine experimental airplane was modified with a RDD Enterprises, LLC, LX7 kit, which included major modifications to the fuselage, wings, empennage, and turbine engine. After the completion of the modifications, the airplane was placed back into the airplane’s Phase 1 operating limitations flight test program for purposes of testing the LX7 conversion. Per the airplane maintenance records, on August 26, 2022, and 11.3 hours since the completion of the modifications, the airplane completed the Phase 1 flight test hour requirements. According to RDD Enterprises, LLC, the landing roll distance is 800 ft (at maximum landing weight), and the landing distance over a 50 ft obstacle is 1,800 ft. The pilot also reported that before delivery and after he acquired the airplane, the airplane sustained several discrepancies and issues, including a door seal that failed during pre-delivery flight testing.