The amphibian was substantially damaged when it impacted terrain in Wilmot, N.H., at about 1500 local time. The Instrument-rated Private pilot was seriously injured; his passenger was fatally injured. Instrument conditions prevailed, but no flight plan was filed. The flight departed the Clinton County Airport (PLB) in Plattsburgh, N.Y., and was en route to the Concord Municipal Airport (CON) in Concord, New Hampshire. The airplane and pilot were located at about 1851 local time, at an elevation of 2490 feet on the western side of Mount Kearsarge, which has a summit of 2937 feet. An area witness reported at the time of the accident that Mount Kearsarge was obscured by a cloud layer from its summit down to about 2000 feet with lateral visibility of about 200 feet. The FAA reported the pilot did not obtain a weather briefing or file a flight plan.