NTSB Factual Report

HISTORY OF FLIGHT

On July 15, 2001, at an estimated time of 1530 Alaska daylight time, a float-equipped Maule M-5-235C airplane, N9237E, sustained substantial damage during a collision with mountainous terrain, about 50 miles south of Bettles, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane was registered to and operated by the pilot. The certificated commercial pilot, and the three passengers aboard, received fatal injuries. A VFR flight plan was filed. The flight originated from the Fairbanks International Airport Seaplane Base, Fairbanks, Alaska, about 0855, and was en route to Lake Sithylemenkat, located about 135 miles northwest of Fairbanks.

During a brief on-scene conversation with the National Transportation Safety Board investigator-in-charge on July 16, the accident pilot's husband related that the purpose of the flight was to show the three passengers aboard some Alaskan scenery. He added that the accident pilot frequently visited Lake Sithylemenkat to hike and pick blueberries.

According to personnel at the Federal Aviation Administration (FAA) Flight Service Station (FSS) at Fairbanks, the pilot obtained a weather briefing, and filed a flight plan with an anticipated return time of seven hours later. The accident pilot activated the flight plan at 0859.

About 1530, an emergency locator transmitter (ELT) signal was received by a search and rescue satellite, emanating from an area about 3 miles southeast of Lake Sithylemenkat. About 1600, a State of Alaska, Fish and Wildlife Protection Officer from Coldfoot, Alaska, aided by other aircraft in the area, began an aerial search in mountainous terrain near Lake Sithylemenkat. About 1800, the wreckage was located about 2,340 feet mean sea level (msl), in an area of mountainous terrain, and along the pilot's anticipated route of departure from Lake Sithylemenkat.

CREW INFORMATION

The pilot held a commerical pilot certificate with airplane single-engine land, airplane multiengine land, and airplane instrument ratings. She held an airplane single-engine sea rating. Her most recent second-class medical certificate was issued on December 5, 2000, and contained the limitation that corrective lenses be worn while exercising the privileges of her airman certificate.

A review of the accident pilot's personal flight records revealed that her total aeronautical experience consisted of about 642.8 hours, of which about 13 were accrued in the previous 6 months. The flight records also revealed that the accident pilot had satisfactorily completed a biennial flight review (BFR) on July 11, four days before the accident.

AIRCRAFT INFORMATION

The airplane had accumulated a total time in service of about 1,207.0 hours. Examination of the maintenance records revealed that the most recent annual inspection of the airframe and engine was accomplished on December 8, 2000, about 27.0 service hours before the accident. Further examination of airframe maintenance records revealed that between September 1999, and March 2000, the accident airplane underwent an extensive airframe overhaul and repair process, about 72.0 service hours before the accident.

The engine had accrued a total time of about 1,207.0 service hours. The maintenance records note that a major engine overhaul was accomplished on March 10, 1992, about 659.0 service hours before the accident.

METEOROLOGICAL INFORMATION

The closest official weather observation station is Bettles, which is located about 50 nautical miles north of the accident site. At 1552, an Aviation Routine Weather Report (METAR) was reporting in part: Wind, 110 degrees (true) at 9 knots; visibility, 10 statute miles; clouds and sky condition, 6,000 feet scattered; temperature, 75 degrees F; dew point, 51 degrees F; altimeter, 29.95 inHg.

The State of Alaska, Fish and Wildlife Protection Officer that was involved in the search for the accident airplane, reported that after locating the wreckage about 1800, he landed his wheel-equipped Piper PA-18 Super Cub along a ridgeline, located about 1,000 feet above the wreckage site. He said that during the approach for landing, he encountered winds out of the southeast, estimated to be 17 to 20 knots. He added that the location of the accident airplane's wreckage was situated on the downwind side of the mountainous terrain. The mountain ridgeline is oriented about northeast-southwest.

COMMUNICATIONS

After the accident flight departed Fairbanks, the accident pilot activated her VFR flight plan. There were no reports of additional communications with the accident airplane.

WRECKAGE AND IMPACT INFORMATION

The National Transportation Safety Board investigator-in-charge, accompanied by two FAA inspectors from the Fairbanks Flight Standards District Office, examined the airplane wreckage at the accident site on July 16, 2001. The airplane was located in an area of mountainous terrain, at an elevation of about 2,340 feet msl, within a "U" shaped valley. The surrounding peaks ranged between 3,000 to 4,000 feet msl. The southwest end of the valley slopes downhill, towards areas of lower, flat terrain.

All of the airplane's major components were found at the main wreckage area. The main wreckage debris path was oriented on a 300 degree heading, and downhill. The nose of the airplane came to rest oriented on a 120 degree heading. (All headings/bearings noted in this report are magnetic).

Postaccident investigation revealed that the nose of the airplane impacted the soft, tundra-covered terrain. The airplane came to rest inverted, with the tail of the airplane positioned downhill of the 15 degree slope, in relation to the main wreckage area.

About 12 feet uphill from the main wreckage site were three impact craters. The two outer most craters measured about 3 feet in diameter, 6 inches deep. About 9 feet uphill from the main wreckage site, the center crater measured about 6 feet by 3 feet, and 13 inches deep.

A 3-inch deep depression was visible in the ground, extending horizontally in front of the three craters. The depression extends from the tip of the left wing, to the tip of the right wing. Both outboard halves of the wings had spanwise leading edge aft crushing with more crushing along the lower portion of the leading edge. Both lift struts remained attached to their respective wing and lower attach points.

The propeller hub remained attached to the engine crankshaft. The three propeller blades were loose in the propeller hub. One propeller blade was almost straight, but displayed slight torsional twisting, and slight aft bending. The second propeller blade displayed about 20 degrees aft bending about 6 inches inboard from the propeller tip, and slight torsional twisting. The third propeller blade displayed about 5 degrees aft bending about 4 inches inboard from the propeller tip, with slight torsional twisting.

The engine cowling, fuselage firewall, and the instrument panel were crushed and displaced aft. The engine was partially buried in the soft, tundra-covered terrain. The engine sustained extensive impact damage to the underside, and lower front portion. The carburetor assembly was broken free from the mounting plate. An internal examination of the carburetor bowl contents revealed about 10 cc of clean, uncontaminated fuel. The fuel sample collected from the carburetor bowl tested negative when subjected to water detecting paste.

The firewall mounted, glass, gascolator bowl was found intact and was completely full of clean, uncontaminated fuel. The fuel sample collected from the firewall mounted gascolator tested negative when subjected to water detecting paste. The gascolator screen was free of contaminants.

Flight control system cable continuity was established from each control surface to the cabin/cockpit area.

The floats were torn from their respective fuselage attach points. The forward nose compartment of each float assembly was crushed aft, and buckled upward.

The main/cockpit cabin area of the fuselage was extensively crushed and distorted. The primary crush zones extended from the firewall area back to about the forward doorpost, and encompassed the pilot and front seat passenger area. The fuselage was buckled and folded, and the empennage was positioned downhill.

The vertical stabilizer, horizontal stabilizer, rudder, elevator, and fuselage, aft of the cabin area, had minor wrinkling, and buckling. The flight control surfaces remained connected to their respective attach points.

The main fuel selector valve was selected to the LEFT fuel tank setting.

On August 9, 2001, an engine examination and disassembly was conducted at Chena Marina Air Service, Inc., in Fairbanks. No preimpact mechanical anomalies were noted during the examination of the engine, or engine accessories.

MEDICAL AND PATHOLOGICAL INFORMATION

A postmortem examination of the pilot was conducted under the authority of the Alaska State Medical Examiner, 4500 South Boniface Parkway, Anchorage, Alaska, on July 17, 2001. The cause of death for the pilot was attributed to multiple blunt force impact.

A toxicological examination was conducted by the FAA's Civil Aeromedical Institute (CAMI) on August 24, 2001, and was negative for any alcohol or drugs.

WRECKAGE RELEASE

The National Transportation Safety Board released the airframe and engine wreckage to the pilot's husband on August 9, at Chena Marina Air Service, Inc., in Fairbanks. The Safety Board retained no components.

NTSB Probable Cause

The pilot's inadvertent stall of the airplane during an unknown phase of flight.