On February 17, 2006, approximately 1410 mountain standard time, a Piper PA-30, N7743Y, piloted by an airline transport pilot, sustained substantial damage during a wheels up landing at the Greeley-Weld County Airport (GXY), Greeley, Colorado. Instrument meteorological conditions prevailed at the time of the accident. The personal cross-country flight from Sioux City, Iowa (SUX), to GXY was operating on an instrument flight rules flight plan under the provisions of Title 14 CFR Part 91. The pilot sustained minor injuries. The passenger on board the airplane was not injured. The flight originated at 1110 central standard time The pilot was cleared for the ILS approach to runway 34 (10,000 feet by 100 feet, dry asphalt) and instructed to contact Greeley UNICOM. The pilot performed a missed approach, contacted Denver Approach Control and informed them that he went missed approach for a "no gear indication." The airplane subsequently circled over the airport in an attempt to get the landing gear to come down. Finally, the pilot performed a wheels up landing on runway 34. During the landing, the airplane's right wing struck a runway sign. The pilot said that about half way to GXY, they heard something vibrate. After 5 minutes the vibration stopped. The pilot said the vibration occurred again later. On the ILS approach into GXY, the pilot said the wheels failed to come down. "I advised approach control and said I intended to circle the field and extend the landing gear manually." The pilot said he "was not successful lowering the wheels. They wouldn't budge." The pilot said that Greeley personnel requested he continue to circle until emergency equipment was in place. "I did, and continued trying to lower the wheels. When the airport people were ready, we landed with the wheels up." The pilot said the temperature en route was "about minus 5 [degrees]." An examination of the airplane showed that it sustained skin scrapes to the nose gear doors and the bottom fuselage. Both propellers' blades were curled and showed chordwise scratches. The right outboard wing bottom skin showed a triangular-shaped tear, located approximately 3 feet outboard of the right engine nacelle. The tear was approximately 1-foot long, chordwise, and 4-5 inches wide. It began just below the leading edge and ran aft. Several stringers were broken and bent aft in the area of the tear. Flight control continuity was confirmed. A post-accident examination of the landing gear system showed no anomalies. A witness that assisted in recovering the airplane following the accident reported that the airframe was covered with ice that measured approximately 3/4 inch thick. At 1355, the weather at GXY was reported as ceilings 400 broken, 5,500 broken, 7,500 overcast, 1-1/2 mile visibility, temperature 2 degrees Fahrenheit (F), dew point -2 degrees F, winds 040 at 16 knots, and altimeter 30.32 inches.