On November 11, 1998, at 1120 Pacific standard time, a McDonnell Douglas MD-11, N801DE, operated by Delta Air Lines as a 14 CFR Part 121 scheduled passenger flight, experienced a tail strike while landing at Portland International Airport, Portland, Oregon. The flight was landing on runway 10R after arriving from Cincinnati, Ohio. Visual meteorological conditions prevailed, and an instrument flight plan had been filed. There were no injuries to the 11 crew members or 113 passengers, but the aircraft sustained substantial damage to the belly skin and stringers. The flight crew stated that they were unaware the aircraft had experienced a tail strike until maintenance personnel at the arrival gate advised them that there was damage to the number 3 VHF antenna and the skin aft of the antenna mount. After the passengers were deplaned normally through the jetway, the damage was further evaluated, and it was determined that the aircraft would need to be ferried to Atlanta for permanent repair. During the investigation, it was determined that the weight existing in the Flight Management System (FMS) during the approach and landing sequence was in error approximately 100,000 pounds. As confirmed by a review of the Flight Data Recorder (FDR) readout, the FMS weight was about 292,000 pounds, when in fact the actual aircraft landing weight was approximately 392,000 pounds. This error generated a final approach speed of 136 knots for an approach that should have been flown at 151 knots. This reduced speed resulted in the approach being flown at an eight (8) degree pitch attitude instead of the three to four degrees that would occur during an approach flown at the correct airspeed. The FDR data also showed that approximately 7 seconds before nose gear strut compression, the pitch attitude reached 10.9 degrees. According to the operator, while landing at this speed and attitude "... tail clearance tolerances are minimal." Although the exact FMS entry error was not determined, the most likely would be the crew missing the hundred thousand entry by one when inputting the takeoff gross weight, entering the empty weight into the zero fuel weight prompt, or entering the zero fuel weight in the aircraft takeoff gross weight prompt. According to the operator, as a result of the lessons learned from this accident, Delta Air Lines is putting additional emphasis on the MD-11 FMS loading procedures during flight training and line checks. In addition, Delta is implementing a program that stresses awareness of proper pitch attitude while in the final approach mode.