On March 13, 2002, about 1553 Alaska standard time, a Piper PA-31-350 airplane, N3527U, sustained substantial damage during an inadvertent wheels-up landing, at the Fairbanks International Airport, Fairbanks, Alaska. The airplane was being operated as a visual flight rules (VFR) scheduled passenger flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated by Warbelow Air Ventures, Inc., of Fairbanks, as Flight 605. The airline transport pilot and the eight passengers were not injured. Visual meteorological conditions prevailed, and the winds were light and variable at the time of the accident. A company VFR flight plan was active. The flight originated at the Fort Yukon Airport, Fort Yukon, Alaska, about 1503. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on March 14, the pilot said as he entered the pattern, he was told by the tower to cross over and enter right traffic for runway 1. The tower then told him he would have to extend downwind because of traffic. The pilot said he made a conscious decision not to put the landing gear down at the usual point because of the request to extend his pattern. He said as he started to extend his pattern, the tower asked him to expedite a base turn, and "keep it tight." The pilot said on the base leg, he again failed to complete his checklist. He said on the final leg of his approach, the airplane behind him said they were too close, and they were going to go around. In the confusion, he said he never completed his before landing checklist, and landed the airplane with the landing gear retracted. The pilot said that fatigue added to his confusion, which lead to the accident. During a telephone conversation with the IIC on March 14, the director of maintenance for the operator said the forward third of the longitudinal stringers and several bulkheads of the fuselage will have to be replaced, due to damage incurred during the accident. He noted that once the airplane was raised off of the runway, the landing gear functioned normally, and the three green landing gear warning lights illuminated. In a letter to the NTSB dated March 14, the pilot reiterated most of his earlier statements. He added that the landing gear warning horn did not activate because of the unusually high power setting used to, "keep it tight," as requested by the tower. He expounded on his earlier statement that fatigue added to his confusion, saying that he had not slept well the night before, and that annual training demands had added to his workload.