HISTORY OF FLIGHTOn September 7, 2019, about 1950 Pacific daylight time, a Beechcraft C-24R, N24030, was destroyed when it was involved in an accident near Las Vegas, Nevada. The pilot receiving instruction and the flight instructor were seriously injured and the two passengers sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 cross-country instructional flight. Neither pilot provided a statement as to the events leading up to the accident. An eyewitness that was located at the north end of the Henderson Executive Airport (HND), Las Vegas, Nevada, was monitoring the tower frequency with a handheld radio. Additionally, he saw the accident airplane taxi near his location and perform a run-up, all while the airplane’s right entry door was open. The airplane’s engine sounded normal during the run-up and the entry door was then closed prior to the pilots receiving takeoff clearance and entering the runway. The eyewitness reported that the airplane appeared to roll down the runway of about 500-600 ft with about 50% power before full power was applied. Shortly after the airplane lifted off the runway. The airplane climbed to about 50 to 100 ft above ground level (agl) and struggled to gain altitude; climbing a few feet and then descending. The eyewitness heard the pilot’s report to the tower on his radio that a door had opened and his request to return to land. The airplane then appeared to climb an additional 50 to 100 ft agl then entered a left turn. Subsequently, the airplane entered a nose-down left bank and impacted the terrain. Air traffic control recordings revealed that the pilot taxied short of runway 17R and performed a runup prior to departure. The pilot reported that he was ready for departure and was then cleared for runway 17R. A few minutes later the pilot reported that a door opened during climb and that he needed to return. The pilot was cleared by the controller to enter right or left closed traffic. No more communication was heard from the pilot. Airport employees reported that the accident airplane arrived at HND around 0800 on the day of the accident and parked at the transient parking for about 1-1/2 hours. The airplane was refueled to a little more than halfway up the fuel tank tabs. A total of 23 gallons of fuel was added to the airplane. Shortly after refueling, four individuals were aboard the airplane when it departed HND and then returned about a 30 minutes later to the transient parking area. An occupant on that flight stated to one of the airport employees that it was too hot, and that the airplane couldn’t climb to get around the mountains. METEOROLOGICAL INFORMATIONAt 1056, HND reported wind was variable at 3 knots, 10 miles visibility, clear skies, temperature at 36°C, dew point 11°C, and an altimeter setting of 29.98 inches of mercury. Later that evening at 1956, HND reported wind from 210° at 12 kts, 10 miles visibility, clear skies, temperature 34°C, dew point 4°C, and an altimeter setting of 29.80 inches of mercury. Density altitude was calculated to be about 5,437 ft msl. WRECKAGE AND IMPACT INFORMATIONExamination of the accident site revealed that the airplane impacted a divided roadway, slid through a steel barrier fence, and came to rest in a culvert drainage area. The empennage separated from the main wreckage just aft of the baggage door area and was found adjacent to the culvert entrance. The main wreckage was partially consumed by post-impact fire. The cabin area and the wing’s inboard sections, including the wing fuel tanks were mostly consumed by post-impact fire. Both entry doors and the baggage door were mostly consumed by post-impact fire. The latch assemblies for all doors were identified and were in the engaged (out) position. The aft baggage door latch strike plate was found and showed normal signs of wear. The latch strike plates for the two entry doors were not found during the examination of the wreckage. The postaccident examination of the airframe and engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. ADDITIONAL INFORMATIONAccording to the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B) Chapter 10, Weight and Balance, excessive weight reduces flight performance in almost every respect. Some of the most important performance deficiencies of an overloaded aircraft include higher takeoff speed, longer takeoff run, reduced rate and angle of climb, and higher stalling speed. According to the C24R Pilot’s Operating Handbook, the emergency procedure for an unlatched door in flight is as follows: If the cabin door latch is not fully engaged, it may come unlatched in flight. This usually occurs during or just after takeoff. The door will trail in a position approximately 3 inches open. A buffet may be encountered with the door open in flight. Return to the field in a normal manner. If practicable, during the landing flare-out have a passenger hold the door to prevent it from swinging open. TESTS AND RESEARCHThe airplane’s estimated total weight at the time of the accident, including about 40 gallons of fuel, four occupant weights and the weight of tools was about 2,835 lbs. The airplane’s takeoff distance was calculated using a performance chart from the airplane’s Pilot’s Operating Handbook. According to the chart, at the airplane’s maximum gross weight of 2,750 lbs, temperature of 34°C, at a pressure altitude of 5,437 ft mean sea level (msl), with a cross wind component of 6 knots, the airplane required a ground roll distance of 1,900 ft and 2,800 ft to clear a 50 ft obstacle. The airplane's maximum rate of climb at maximum gross weight would have been about 525 ft per minute (fpm). The airplane was loaded over the max gross takeoff weight and aft of the center of gravity moment envelope for both flights.