On February 16, 2004, at 1426 eastern standard time, a Cessna 210E, N4974U, was substantially damaged while landing at Allegheny County Airport (AGC), Pittsburgh, Pennsylvania. The certificated commercial pilot and the passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, conducted under 14 CFR Part 91. According to the pilot, who was also the airplane's owner and mechanic, the left main landing gear would not extend into a down and locked position. The pilot decided to land with the right main and nose landing gear in the down and locked position, and the left main landing gear "hanging." Upon touchdown, the left main landing gear collapsed, and the airplane slid off the left side of the runway. According to a Federal Aviation Administration (FAA) inspector, a post-accident examination of the airplane revealed that the left main landing gear saddle was fractured. The landing gear saddle was the subject of an Airworthiness Directive (AD), AD 76-14-07 R2. The AD required replacement of the landing gear saddle, and after 1,200 hours of service on the new part, annual dye penetrant inspections. The FAA inspector's review of the airframe logbook revealed that the part was replaced in 1976, and was due for its first dye penetrant inspection in 1986. There were no records in the logbook to indicate that an annual inspection of the part had ever been performed. The landing gear saddle was submitted to the Safety Board Materials Laboratory for examination. According to the engineer's factual report, the saddle fracture surfaces exhibited features consistent with fatigue. There was also no visual evidence of any dye penetrant on the part.