On April 15, 2009, approximately 1000 mountain standard time, a Cessna 152, N6285M, sustained substantial damage when it impacted a fence during a forced landing in Glendale, Arizona. The flight instructor and his student pilot received minor injuries. Air Safety Flight Academy was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the local instructional flight, which had originated from the Glendale Municipal Airport about 0830. A flight plan had not been filed. The flight instructor reported that he and the student pilot had completed a series of flight maneuvers. While returning to the airport, the engine began running rough. The flight instructor applied carburetor heat and slightly leaned the mixture, and the engine roughness stopped. As the airplane neared the airport, the engine again began running rough, and the roughness became "increasingly worse." The flight instructor applied carburetor heat and requested priority to land. Shortly after, the engine "sputtered briefly and died." The flight instructor was unable to restart the engine and initiated a forced landing onto a grassy field. During the landing roll, the airplane impacted a chain link fence. The right wing was bent and wrinkled, and the nose wheel was bent aft. The airplane was examined under the supervision of a Federal Aviation Administration (FAA) inspector. To facilitate an engine run, the propeller was replaced. Despite several attempts, the engine would not operate. The magnetos were removed for inspection. Both magneto impulse couplings were snapped several times and both magnetos failed to produce spark. Both magnetos were placed on a test stand and run at various speeds. Both magnetos failed to produce spark. Disassembly of the left magneto revealed that the condenser was within manufacturer limits, and the points were set correctly. The coil was inspected and tested, which revealed a complete failure of the secondary coil. The coil also displayed thermal discoloration near the rotating magnet. The right magneto was disassembled and inspected. The right magneto also displayed thermal discoloration, but to a lesser degree. The primary and secondary coils were tested and no anomalies were noted. The internal timing of the magneto was tested and revealed the "EGap" was set incorrectly. The points were off center and not opening completely. Further inspection revealed that the lead connector from the magneto's coil to the points was loose. After, the magneto was retimed to manufacturer's specifications and the lead reinstalled on the points, the magneto operated normally on the test stand. Review of the engine maintenance logbook revealed that on April 13, 2009, at a tachometer time of 3,107.5 hours, a 100-hour inspection was performed. Review of the company maintenance work order for the 100-hour inspection indicated that a 12-month magneto inspection was completed. The work order indicated that "serviceable" magnetos with new contact points, capacitors, and gaskets were reinstalled. The FAA inspector reported that the tachometer reading at the time of the accident was 3,110.5 hours.