On October 11, 1999, about 1330 Alaska daylight time, a Piper PA-31 airplane, N74923, sustained substantial damage when it struck a bird during cruise over Skilak Lake, Alaska, about 15 miles east of Soldotna, Alaska, at 60 degrees 27 minutes north latitude, 150 degrees 29 minutes west longitude. The solo airline transport pilot was not injured. The flight was conducted under 14 CFR Part 135 as scheduled commuter Flight 13. The flight departed the Anchorage International Airport, Anchorage, about 1300 for Seward, Alaska. Visual meteorological conditions prevailed at the time of the accident, and a company VFR flight plan was filed. During a telephone interview with the NTSB investigator-in-charge (IIC) on October 12, the pilot stated that while in cruise at 2,500 feet above sea level (msl), the airplane shuddered. He noticed blood on the end of the right horizontal stabilizer, and realized the airplane had struck a bird which he had not seen. He said the airplane did not require any trim changes after the impact. The pilot returned the airplane to Anchorage. A postflight inspection revealed substantial damage to the airplane's right horizontal stabilizer, requiring replacement of the stabilizer assembly.