Accident Overview
On May 27, 2017, about 1122 Alaska daylight time, an Arctic Aircraft Company S-1B2 airplane, registration N57AT, impacted terrain following a loss of control approximately 35 miles east of Salcha, Alaska. The private pilot and a passenger sustained fatal injuries, and the airplane was substantially damaged. The flight was conducted under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The airplane departed from an off-airport landing site near Fairbanks, Alaska, about 0925.
Purpose of the Flight
According to a family member of the pilot, the flight aimed to search for an overdue boat piloted by a relative of the passenger, with the intention of landing at a remote unimproved airstrip near the boat's destination. The boat had left the previous evening for a recreational cabin along the Salcha River.
Witness Observation
A witness reported observing the airplane circle the remote airstrip along the Salcha River. While circling, the nose suddenly dropped, and the airplane descended in a near-vertical attitude. The engine continued to run, and no unusual sounds were heard except for an increase in engine rpm during the descent. Strong wind conditions prevailed at the time.
Pilot Information
The pilot, aged 81, held a private pilot certificate with an airplane single-engine land rating. His most recent third-class medical certificate was issued on September 30, 2015, with a requirement to wear corrective lenses. Personal flight records were incomplete; his aeronautical experience, based on FAA records, showed that on his August 7, 2013, medical application he reported about 1,960 total flight hours, with 60 hours in the previous six months. He did not report flight experience on his most recent medical application.
Aircraft Information
The 1978 model Arctic Aircraft S-1B2 had a total time in service of 3,087.50 flight hours. The most recent annual inspection of the airframe and engine was completed 27.10 flight hours before the accident on June 9, 2016. The aircraft was equipped with a 160-horsepower Lycoming O-320 B2B engine, which had accumulated 1,748.00 hours since overhaul.
Meteorological Conditions
The closest official weather observation station, Eielson Air Force Base, about 35 miles east of the accident site, reported at 1058: wind calm, visibility 10 statute miles, clouds and ceiling 10,000 ft broken, temperature 52°F, dew point 27°F, and altimeter 30.04 inches of mercury.
Wreckage and Impact
The wreckage was located in an area of black spruce trees and tundra-covered terrain at an elevation of about 1,000 ft mean sea level. The airplane impacted in a near-vertical attitude, with the nose on about a 110° magnetic heading. All major components were found at the main wreckage site. The cockpit area was extensively damaged; the engine, firewall, and instrument panel were displaced upward and aft. The mixture control was full forward, and carburetor heat was off.
The right wing remained attached, with about 2 feet of the outboard portion exhibiting extensive leading edge aft crushing. The left wing separated at the rear attach point but remained attached at the forward attach point. Flaps remained attached; the right flap was crushed against the fuselage and bent about 20° down. The left flap was relatively undamaged. The horizontal and vertical stabilizer, elevators, and rudder were attached and free of impact damage.
Flight control continuity was verified from the cockpit to the elevators and rudder. Aileron control continuity was established in direct cables from the cockpit to the right aileron and through a disassembled turnbuckle to the left aileron. The balance cable fractured with features consistent with tension overload.
The engine sustained impact damage but examination revealed no anomalies, contamination, or evidence of malfunction. Cylinders, pistons, valve train, crankshaft, and internal components showed no precluding malfunction. Both magnetos produced spark in rotational order. The propeller remained attached by two of six bolts; one blade exhibited torsional "S" twisting and light chordwise scratching, the other had light scratching and aft bending near the tip.
No evidence of mechanical malfunctions or failures precluding normal operation was found in the airframe or engine.
Medical and Pathological Information
An autopsy of the pilot conducted by the Alaska State Medical Examiner on May 30, 2017, attributed the cause of death to multiple blunt force injuries. Toxicological testing by the FAA was negative for carbon monoxide and alcohol but revealed unspecified levels of verapamil (a calcium channel blocker) in blood and liver, and its active metabolite norverapamil in blood. Verapamil is used to treat high blood pressure, angina, and arrhythmias.
GPS Data
The pilot was using a Garmin Aera portable GPS receiver. Data logs for May 27, 2017, showed the flight departed the remote site about 0925:30, proceeded southeast along the Tanana River, then east up the Salcha River. The last fully recorded GPS point at 1122:39 indicated the airplane at 1,705 ft GPS altitude, heading 132° true, and 47 knots ground speed.
Weight and Balance Estimate
An estimated weight and balance was calculated using pilot weight from his last medical (184 pounds), passenger weight from driver's license (170 pounds), and items onboard: two backpacks (25 lbs total), 24-pack water (27 lbs), six bottles wine (17 lbs), frying pan (0.5 lbs), eight-pack paper towels (4 lbs), three patio pillows (3.5 lbs), estimated fuel (10 gallons, 60 lbs), and oil (8 quarts, 15 lbs). The basic empty weight of the airplane on wheels was 1,274.50 pounds as of May 29, 2015.
The gross weight at the time of the accident was estimated to be 1,780.5 pounds, which exceeded the approved maximum takeoff gross weight of 1,650 pounds by 130.5 pounds. The estimated center of gravity was 15.896 inches, while the center of gravity range at maximum gross weight is 11.0 to 15.8 inches.
Probable Cause
The investigation did not state a probable cause.