NTSB Factual Report

On July 23, 2007, about 1830 mountain daylight time, a de Havilland Beaver DHC-2 MK.1, N6784L, traversed through rocks and a stream while making a forced landing due to a loss of engine power in the Bob Marshall Wilderness near Kalispell, Montana. The student pilot/owner operated the airplane under the provisions of 14 CFR Part 91 as a personal flight. The commercial pilot, student pilot/owner, and one passenger received minor injuries; the airplane sustained structural damage during the emergency landing. Visual meteorological conditions prevailed for the cross-country flight that departed Skagit Regional Airport (BVS), Burlington/Mount Vernon, Washington, about 1400 Pacific daylight time. No flight plan had been filed. The flight was destined for Oshkosh, Wisconsin, with an intermediate fuel stop at Lewiston Municipal Airport (LWT), Lewiston, Montana.

According to the owner, the fuel tanks were full upon their departure from BVS. They were about 4 hours into the flight at 8,000 feet, when the engine began to sputter, and then quit. They went through the emergency procedures, which included switching fuel tanks and engaging both the hand operated wobble and electric fuel pumps. They started to look for a clear area to land. The airplane landed on "rough" gravel, and went through water to an opposite rising gravel bar, where the airplane went up on its nose before it came to rest upright on its landing gear. The owner stated that the engine sounded more like it was having an "ignition problem," rather than a fuel issue.

The commercial pilot reported that he was the flying pilot. During the flight the airplane had been running well; they were about 3 hours 20 minutes into the flight when the engine problems began. He stated that they were at 8,000 feet when the engine sputtered two times and then quit. With the assistance of the other pilot, they conducted the emergency procedures, which included an attempt to restart the engine. The pilot stated that the oil pressure and cylinder head temperature gauges were in the green prior to the event, and there was no indication of a pending event.

According to recovery personnel from Northwest Tower, Inc., a visual examination of the engine revealed that the master rod end had broken. Recovery personnel also reported that the firewall was wrinkled, and one of the main landing gear and a door post were "tweaked," one of the rear wing spar's was bent, and one of the horizontal stabilizer's had sustained rock damage at the leading edge. They recovered 24 gallons of fuel from the front tank, 28 gallons of fuel from the middle tank, and no fuel in either the tips or rear fuel tanks. Recovery personnel further reported that there were no pieces of metal noted in the oil sump or oil filter.

The engine was transferred to Kenmore Air, Seattle, Washington, for repairs. Maintenance personnel noted that the supercharger impeller shaft (blower bushing) bearings had failed. They further indicated that if the engine has sat for any length of time, the engine should go through a pre-oil prior to starting to make sure the engine has been lubricated sufficiently. The blower bushing requires lubrication, and if it fails, raw oil can be pumped into the induction system.

NTSB Probable Cause

A loss of engine power due to the failure of the supercharger impeller bushing, which allowed raw oil to enter the induction system.