On November 7, 1996, approximately 1630 mountain standard time, a Piper PA-28-151, registered to and operated by Rocky Mountain Air, Inc., and being flown by a commercial pilot, was substantially damaged when the right main and nose landing gear collapsed during the takeoff roll from a dirt road near Bruneau, Idaho. The accident site was approximately 60 nautical miles south of Nampa, Idaho. The pilot and two passengers were uninjured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was a sightseeing flight, was to have been operated under the requirements set forth in 14CFR135.1(b)(2) and originated at Nampa, on the afternoon of the accident. The pilot reported to an FAA inspector that he made an off-airport landing on a 2,500-foot stretch of dirt road due to the physiological needs of the passengers. Prior to attempting the takeoff, he did not perform takeoff-distance calculations to ensure that the aircraft could successfully get off the ground from the available surface. During the takeoff roll, the aircraft reached the end of the available road before becoming airborne, and impacted a shallow dirt bank. The impact resulted in the nose landing gear folding aft and the right main landing gear separating from the right wing. The NTSB was notified of the event on November 8, 1996, approximately 0800. The damage assessment was defined as minor at that time. Further assessment by FAA maintenance personnel revealed substantial damage and the Board's Northwest Regional Office was notified of the upgrade on November 18, 1996, at 0800.