On May 9, 2005, about 1645 Alaska daylight time, a wheel-equipped Piper PA-31-350 airplane, N3535F, sustained substantial damage as the result of an in-flight fire in the right engine during cruise flight between Nome, Alaska, and Elim, Alaska. The fire was detected by the pilot during the landing roll at Elim. The airplane was being operated as a visual flight rules (VFR) scheduled domestic passenger flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated as Flight 310, by Cape Smythe Air Service Inc., Barrow, Alaska. The airline transport certificated pilot, and the six passengers, were not injured. Visual meteorological conditions prevailed, and a VFR flight plan was filed. The flight originated at the Nome Airport, about 1605. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on May 10, the vice president of operations for the operator reported that when the fire was noticed by the pilot after landing at Elim, he pulled the firewall fuel shutoff for the right engine and stopped the airplane. The passengers were evacuated and the pilot discharged the airplane's fire extinguisher inside the right engine compartment. Additional dry chemical fire extinguishers were supplied by personnel at the airport, and the fire was extinguished. The airplane received structural damage to the right wing and right flap. A passenger on the airplane, who was seated in the aft, left seat, informed a Federal Aviation Administration (FAA) airworthiness inspector from the Fairbanks Flight Standards District Office (FSDO), that she "smelled gas and smoke as the airplane was turning into land (final approach). I saw flames as the plane landed, on the right side." The FAA inspector examined the airplane in Elim. He reported that the fire pattern was consistent with an in-flight fire on the inboard side of the right engine, that appeared to be concentrated around the hydraulic pump, fuel pump, and the turbocharger. The inspector examined the fuel lines and hydraulic lines to the respective pumps. His examination revealed loose "B" nuts that had no heat discoloration. The airplane's hydraulic fluid reservoir contained fluid. The inspector noted that the airplane's right engine hydraulic pump was replaced during a 50 hour inspection, about 31 hours before the fire. The inspector interviewed the operator's maintenance personnel, and learned that during the hydraulic pump replacement, mechanics removed the right engine's fuel pump to facilitate access to the hydraulic pump. Due to the confined area during the reinstallation of the feeder line to the fuel pump, one mechanic held the line in-place, and another turned the fitting with a wrench. A leak check revealed that the fitting was cross-threaded and leaked. The fitting was re-tightened and signed off. The inspector sent the fuel lines and hydraulic lines to the NTSB IIC for examination. Each line was subjected to an air pressure leak test at a local maintenance facility, and no leaks were discovered. According to the pilot, he completed a Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) and sent it to the operator's corporate office in Barrow, Alaska. The operator was unable to locate the report, and the operator is now under new ownership. A copy of the pilot's statement, the FAA inspector's description of his findings, and a passenger statement, are included in the public docket for this report.