On August 19, 2002, about 0900 Alaska daylight time, a tundra-tire equipped Maule M-7-235 airplane, N897M, sustained substantial damage when the right main landing gear axle broke during landing roll on rough and uneven terrain on a mountain ridge top, located about 15 miles east of Palmer, Alaska. The airplane was being operated as a visual flight rules (VFR) on-demand charter flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated by Grasshopper Aviation, Wasilla, Alaska. The certificated commercial pilot, and the two passengers, were not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight originated at the Palmer Airport, Palmer, about 0840. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on August 19, the pilot reported that he was landing to the north on a mountain ridge top. He said that during the landing roll, the right main landing gear axle broke allowing the right wheel to separate from the airplane. The airplane pivoted to the right, and the left wing struck the ground. The airplane sustained substantial damage to the wings and fuselage. The airplane was retrieved from the accident site and transported to Palmer by company and insurance personnel. A Federal Aviation Administration (FAA) airworthiness inspector, Anchorage Flight Standards District Office, traveled to the operator's maintenance facility, and examined the fractured landing gear axle. The FAA inspector reported that the operator utilized a set of Schneider Fixed Penetration Wheel/Skis, model SWS-4000, during the winter time. The initial installation of the wheel/ski kit was accomplished under the FAA's Major Repair and Alteration process, FAA Form 337. The FAA inspector added that during the initial wheel/ski kit installation process, a 3/8-inch hole was drilled through the axle. The FAA inspector said that a visual inspection of the fractured landing gear axle revealed the fracture trail traveled through the drilled hole in the axle. He added that there was a substantial amount of corrosion and rust within and around the fracture surface. According to the NTSB Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the operator, the airplane had accumulated about 2,504.5 hours in service. The operator noted that the time in service of the failed landing gear axle was about 2,500 hours in service, and the time since inspection was about 1,800 hours.