On August 11, 2019, at 1448 eastern daylight time, a Schweizer 269C-1, N1831A, was substantially damaged when it was involved in an accident near Allentown, Pennsylvania. The commercial pilot sustained serious injuries and the passenger sustained minor injuries. The helicopter was operated by Ace Pilot Training Inc., as a Title 14 Code of Federal Regulations Part 91 sightseeing flight. According to air traffic control, several minutes after being cleared for takeoff, the pilot transmitted via radio, "mayday, mayday, mayday, three one alpha going down." The helicopter subsequently collided with a building shortly thereafter. The pilot and passenger did not provide any statements regarding the circumstances or events that transpired during the flight. Examination of the helicopter by a Federal Aviation Administration inspector revealed that the helicopter came to rest in a grassy area on the side of the building. The cockpit was impactdamaged. All three main rotor blades remained attached to the main rotor hub and were buckled. The tail boom was buckled and impact damaged. The tail rotor blades were buckled and remained attached to the tail rotor gearbox. Engine valve train continuity was established. The accessory section of the engine revealed some impact damage. A review of the maintenance logbooks revealed that the engine was installed from another helicopter that was involved in an accident on May 17, 2017. At that time, the left magneto was newly installed. On July 25, 2018, the right magneto was replaced as a used-serviceable unit with no previous history or time in service information. The right magneto accumulated 195.6 hours on the engine since installation. Following the accident, the right magneto could not be bench tested due to impact damage. The harness cap was removed and exhibited severe corrosion and indications of misfiring on the distributor block and the No. 2 insulator. The coil was in good condition with the exception of the bent tab; both primary windings and secondary windings were within allowable limits. The condenser was undamaged and functioned satisfactorily. Examination of the left magneto revealed minor damage on the housing. The magneto was bench tested and failed all sections of the testing. The magneto produced intermittent and weak sparks at all test settings. The left magneto was opened, and the components were inspected. The coil was in good condition and the primary and secondary windings were both within allowable limits. The condenser was undamaged and functioned satisfactorily. The points were worn but in good condition. An attempt was made to reset the E-gap with the old cam installed, but it was worn and did not allow proper function. The distributor block was serviceable and showed minor wear. A new cam was installed, the E-gap reset, and the magneto was retested, during which it performed nominally. The magneto had accumulated 578.8 hours time in service on this engine. There was no indication or logbook entry of a 500-hour inspection being completed. There were also no indications that the Slick/Champion Aerospace Service Bulletin SB1-15A, for replacement of the distributor block, had been completed.