History of Flight
On May 30, 2015, about 1130 Alaska daylight time, a Cessna 207, registration N1653U, sustained substantial damage after impacting trees about 40 miles southeast of Bethel, Alaska. The airplane was being operated by Yute Air as a visual flight rules post-maintenance flight under Title 14 CFR Part 91. The commercial pilot, the sole occupant, sustained fatal injuries. Visual meteorological conditions were reported, and company flight following procedures were in effect. The flight originated at Bethel Airport about 0830, with an expected return time of 1200.
About 1415, flight coordination personnel notified the director of operations that the airplane was overdue. About 1435, the FAA was notified and issued an alert notice. An aerial search was initiated about 1532 by Yute Air, Alaska State Troopers, Alaska Air National Guard, and others. On May 31, about 1730, searchers discovered the airplane's submerged and fragmented wreckage in a swift-moving river slough.
Personnel Information
The pilot, age 47, held a commercial pilot certificate with airplane single- and multi-engine land ratings. His most recent second-class medical certificate was issued on April 14, 2015, with no limitations. According to company records, he had about 7,175 total flight hours, with about 6,600 hours in the accident airplane make and model. In the preceding 90 and 30 days, he had flown 362 and 94 hours, respectively. He was hired on June 9, 2010, and had completed an airman competency/proficiency check on January 20, 2015, in a Cessna 207. The accident flight was his first of the day, on the second day of a two-week on-duty rotation.
Aircraft Information
The Cessna 207, serial number 20700253, was manufactured in 1974. It was powered by a Continental Motors IO-520-F engine, serial number 810024-R, rated at 300 horsepower, and equipped with a Hartzell controllable-pitch propeller. The last inspection was a 100-hour inspection on May 29, 2015, at which time the airframe had 28,211.4 total hours. The engine had 6,296.9 hours, 537.8 hours since overhaul. All six engine cylinders were replaced just before the flight, and the purpose was to break them in per Continental Motors guidelines.
On September 23, 2013, a "Winter Heat Kit" was installed, including an additional air induction box, ducting, heat shroud, and Y duct. The exhaust system was not in compliance with manufacturer specifications. The modification required an FAA Form 337 Major Repair and Alteration, but no such documentation was found. During a May 2013 inspection of Yute Air, a Cessna 207 with the modification was discussed between the PMI and the DOM. The PMI understood it was a "work in progress," while the DOM believed a verbal agreement had been made.
Meteorological Information
The closest weather reporting facility was Bethel, about 40 miles northwest. At 1053, a METAR reported wind from 210 degrees at 10 knots, visibility 10 statute miles, few clouds at 12,000 feet, scattered at 2,000 feet, temperature 16°C, dew point 9°C, altimeter 30.12 inHg.
Wreckage and Impact Information
The main wreckage was submerged in the Kwethluk River at 244 feet msl, coordinates N60.20.123, W161.03.256. An initial impact point was marked by a broken treetop on a 30-foot birch tree, with a right wing tip fragment beneath. The fuselage came to rest inverted on its left side, submerged in fast-flowing water about 270 feet from initial impact, on a magnetic heading of 010 degrees. The engine and propeller separated and were found submerged upstream.
Examination on August 5, 2015, found flight control continuity. The throttle, propeller, and mixture controls were full forward; cowl flaps intermediate; fuel selector on left tank; fuel pump off. Fuel tanks were bladders with unobstructed vents and secure caps. An engine teardown revealed no preimpact mechanical malfunction or failure. An ASA carbon monoxide spot detector was on the instrument panel, opened 09/2013, with instructions to replace every 90 days.
Medical and Pathological Information
A postmortem examination attributed the pilot's cause of death to blunt force traumatic injuries. Toxicology was negative for ethanol but revealed 21 percent carboxyhemoglobin (carbon monoxide) in the blood. The pilot was reported to be a nonsmoker. The NTSB's chief medical officer reviewed the autopsy and toxicology.
Search and Rescue
When the airplane failed to arrive, company personnel initiated telephone and satellite phone searches. Management contacted the Air Force Rescue Coordination Center. The airplane was not equipped with a 406 MHz ELT; analog 121.5 MHz ELTs were no longer monitored by satellites as of February 2009. The fragmented, submerged wreckage was spotted on May 31 about 1730 by former Yute Air pilots volunteering in the search.
Tests and Research
A pressure test on the right muffler/heat exchanger revealed no leaks. The additional muffler/heat exchanger from the Winter Heat Kit was missing and not found at the accident site. ADS-B data showed the airplane operated below 500 feet msl for most of the three-hour flight, with the last return at 23 miles southeast of the site at 1,075 feet msl.