On November 13, 2000, at approximately 1100 mountain standard time, a Mooney M20J, N201JP, was substantially damaged during landing at Vance Brand Airport, Longmont, Colorado. The flight instructor and private pilot receiving instruction both received minor injuries. The airplane was being operated by Jeffco Flight School, Broomfield, Colorado, under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country flight that originated from Broomfield, Colorado, approximately 30 minutes before the accident. The flight instructor had not filed a flight plan. The flight instructor said that the flight was a rental check out. He said that after 30 minutes of air work, they approached Longmont's airport for some touch and go landings. He said that the student was flying the airplane, and that the approach was uneventful. The flight instructor said that as soon as the airplane was on the ground, it turned sharply to the left. The student said that the flight instructor took control of the airplane, but he could not prevent its departure from the runway. The airplane impacted a 6-foot high snow bank and bent the left wing up, approximately 5 feet from the tip. Postaccident investigation revealed that the left main landing gear had separated from the airplane immediately upon touch down. Examination of its strut revealed that it was corroded approximately 1/3 of the way through.