NTSB Factual Report

HISTORY OF FLIGHT

On August 23, 1996, at 2030 Alaska daylight time, a float equipped Maule M-7 airplane, N5656A, registered to and operated by the pilot, crashed on a gravel bar on the Nigu River located approximately 135 nautical miles south of Barrow, Alaska. The personal flight departed Etivluk Lake for a local flight. No flight plan was filed and visual meteorological conditions prevailed. The certificated commercial pilot and the passenger received fatal injuries. The airplane was destroyed by post impact fire.

WITNESSES

Two witnesses were camped in the Howard Pass area of the Brooks range. Their campsite was located approximately 15 miles west, northwest of the accident site. In a statement dated August 29, 1996, they related the following information: "Last Friday evening we observed an airplane with floats flying first in a southwesterly direction over the Etivluk River then back to the Northeast direction over the same river. The plane was flying very low." The witness and his son stated they wondered what an airplane was doing flying in this sort of weather. They described the wind as "horrendous." They estimated the wind to 80 knots. They described water flying off the whitecaps on the lake for "tens of yards." They tried to stand in the wind and they had to lean so far forward that they felt like they were "ski jumping." Neither saw the airplane crash.

INJURIES TO PERSONS

Both occupants were fatally injured.

DAMAGE TO AIRCRAFT

The airplane fuselage was destroyed by post impact fire. The right wing remained attached to the fuselage cabin top tubing. The wing's leading edge was crushed rearward along the chord line. The left wing was missing from a point outboard of the upper wing strut attach points. A portion of the spar, just outboard of the upper wing strut attach points was curled upward and was pointing toward the cabin of the airplane. The upper 18 inches of the left wing struts were also curled toward the airplane's cabin. The upper and lower skin surfaces of the left wing, inboard of the upper wing strut attach points, were burned away. Upper wing skins from the left wing were located more than 3/4 of a mile away.

The floats were fire and heat damaged and were resting on the wreckage inverted. The tail section and empennage were inverted and void of any skin.

PERSONNEL INFORMATION

According to the Federal Aviation Administration's medical records, the pilot indicated on his last medical application, dated August 19, 1995, that he had a total of 11,800 hours and had flown 200 hours in the previous six months.

AIRCRAFT INFORMATION

According to an airplane logbook entry, the airplane received an annual inspection on May 8, 1996 and had a total time of 495.0 hours. It is not known how much the airplane flew since that inspection.

The Maule M7 airplane has a wingspan of 33 feet, 2 inches. The Maule M5 airplane has a wingspan of 30 feet, 10 inches. The thickness of the wing skin panels and the size and spacing of the rivet patterns remained the same for both type airplanes. The Maule M7 airplane has the option to have outboard wing fuel tanks installed near the wing tips.

METEOROLOGICAL INFORMATION

There are no weather reporting facilities in the proximity of the accident site. There were no pilot reports made near the area. The area forecast for the northern slopes of the Brooks Range called for moderate turbulence below 6,000 feet above mean sea level.

WRECKAGE AND IMPACT INFORMATION

The main wreckage was located on a gravel bar on the Nigu River. The nose and engine of the airplane were buried in the gravel bar. The tail of the airplane was resting on top of the wreckage, inverted, and was pointing 054 degrees magnetic. The wreckage path was oriented between 018 degrees and 067 degrees. The debris in the wreckage path consisted of a section of the left wing leading edge, wing strut attach point cuff, inspection plates, top skin of fuel tank, inboard leading edge, outboard portion of the top skin from the left wing. The latter piece was located 3/4 of a mile from the main wreckage on a magnetic bearing of 043 degrees from the main airplane wreckage.

The wreckage was examined and flight control continuity was established. The left aileron remained attached to portions of the rear spar, but it was damaged by fire.

The propeller was examined and one blade was broken from the hub near the root of the blade. Both blades had chordwise scoring and pieces of metal missing from the leading edges. The engine crankshaft was broken near the propeller flange and was separated from the engine.

The red navigation lens was found near the wreckage. It was not broken and was sooted inside. There was no filament remaining in the bulb associated with the red navigation lens. The green lens was not found, and the socket was sooted.

The instrument panel and cockpit area was destroyed by fire.

TEST AND RESEARCH

The following pieces of wreckage were submitted for metallurgical examination at the National Transportation Safety Board's metallurgical laboratory in Washington, D.C. :

Four pieces of left wing front spar were submitted for examination. According to the NTSB metallurgist who examined the wreckage, all fracture surfaces displayed surfaces typical of over stress.

Two pieces of leading edge skin recovered in the wreckage path were also submitted. The rivets that held the piece to the wing had pulled through the sheet metal across the entire leading edge piece. In some areas, the metal between the rivet hole and the aft edge of the piece had sheared.

A section of the left wing upper skin panel was examined. The rivets along the forward edge of the panel pulled through the rivet holes in the skin panel. The aft end of the panel was curled.

Two pieces of the inboard fuel tank upper skin were examined. They were wrinkled and buckled in the inboard-outboard direction. The rivets along the leading edge of the skin pulled through the rivet holes. The sheet metal along the aft end of the skin separated from each rivet hole to the aft end of the skin.

ADDITIONAL INFORMATION

Transportation to the accident site was provided by the North Slope Borough Search and Rescue Group. Because of fuel restrictions, there was a limited time available at the accident site.

NTSB Probable Cause

the pilot's inadequate weather evaluation and resultant flight into adverse weather conditions. Factors associated with the accident were: high winds and terrain induced turbulence.