On January 26, 2002, about 0910 Atlantic standard time, a Cessna 172P, N99295, registered to the Civil Air Patrol, Inc., operating as a Title 14 CFR Part 91 instructional flight, crashed while maneuvering in the vicinity of Levittown, Puerto Rico. Visual meteorological conditions prevailed and no flight plan was filed. The aircraft received substantial damage, and the private-rated pilot and commercially-rated safety pilot received minor injuries. The flight departed San Juan's Isla Grande Airport about 5 minutes before the accident. According to the pilot, shortly after departure, he gave control of the aircraft to his safety pilot while he donned and adjusted the "foggles". They both felt a jolt, and the safety pilot stated that he had lost aileron control. The pilot retook aircraft control and commanded the safety pilot to declare an emergency and communicate with ATC while he chose a suitable field to perform an emergency landing. An attempt to turn the aircraft into the wind using rudder only was abandoned, and the pilot decided to land the aircraft straight ahead. The touchdown was to a swampy area, and the left wing and nose strut were substantially damaged. According to FAA inspectors, postcrash examination of the aircraft revealed a separated left aileron main control cable above the cockpit headliner at a turning pulley near the left rear door post. The fractured cable was removed and sent to the NTSB Materials Laboratory for failure analysis. According to the NTSB Materials Laboratory report, detailed examination of the individual wire strands that form the .125 inch diameter, 7X19 constructed aileron control cable revealed extensive corrosion damage at the broken wire ends, with many of the wires corroded completely through. One of the wire strands was corroded completely through about 1 inch from the primary separation. The laboratory report is an attachment to this report. Aircraft maintenance records revealed that the aircraft underwent an annual inspection on October 11, 2001 at a total aircraft time of 2170.0 hours, or 31.2 hours prior to the accident. The Cessna model series 172 service manual calls for 200 hour inspection intervals for aileron cable tension, routing, fraying, corrosion, and turnbuckle safety.