Accident Details
On November 20, 2021, at about 1755 Alaska standard time, a Cessna 207 airplane, registration N9794M, operated by Yute Commuter Service as a Title 14 Code of Federal Regulations Part 135 scheduled passenger flight, sustained substantial damage following an accident near Bethel, Alaska. The pilot and five passengers were not injured. The flight was destined for Kwethluk, Alaska, about 12 miles east of Bethel, carrying passengers and cargo.
Pilot Actions
Shortly after departure, the pilot noticed that the red emergency locator transmitter (ELT) light on the instrument-panel-mounted remote switch had illuminated. The pilot asked the Bethel tower operator if they were receiving an ELT signal; the tower operator responded that no signal was being received. Moments later, the pilot smelled an electrical burn odor and decided to return to Bethel. About one minute later, the smell intensified, and visible smoke appeared in the cockpit. The pilot declared an emergency to Bethel tower, turned off the airplane’s master electrical switch, and opened his side window for ventilation. He briefly turned the master switch back on to again declare an emergency and inform the tower of his intention to land on runway 1L.
During the landing roll, the pilot realized that the nosewheel steering system and brake system were both inoperative. After the airplane rolled to a stop on the left side of runway 1L, he ordered all passengers to evacuate. After all occupants had safely exited, heavy smoke filled the cockpit and passenger compartment, and a candle-like flame appeared behind the pilot and co-pilot seats, just beneath the floorboards. Moments later, the airplane was immediately engulfed in flames.
Postaccident Examination
Maintenance records indicated that on January 27, 2011, the Capstone system, phase 1, was installed on the accident airplane under Federal Aviation Administration (FAA) Supplemental Type Certificate (STC) number STC2154AK. The Capstone Program is a voluntary safety demonstration involving installation of avionics suites in approximately 200 aircraft operated in western Alaska. The suites, manufactured by UPS Aviation Technologies, include an MX-20 multifunction display, GX-60 GPS nav/com, Universal Access Transceiver, and installation kit with cables, antennas, mounting hardware, and an instruction book.
NTSB postaccident examination revealed the fire origin behind the pilot’s row of seats, where a wire harness, part of the Capstone equipment, was found improperly installed on top of the aft fuel line from the left fuel tank. The fuel line exhibited chafing and thermal damage. After removal, a small pinhole was detected in the fuel line using a flashlight. NTSB Materials Laboratory examination of the wire harness found a range of thermal and electrical damage, from discoloration and sooting to beading and welding in areas on individual conductors. The damage was consistent with the wire being energized at the time the damage occurred.
During on-scene examination, a second Cessna 207, purchased at the same time as the accident airplane, was examined in the operator’s hangar. The NTSB investigator-in-charge and entire investigative team discovered that the same Capstone wire harness condition found in the accident airplane existed in the second Cessna 207 in the same location.
Regulatory Response
As a result of the investigation, the FAA issued a notification letter to alert registered aircraft owners and operators of the need to inspect the area inside inspection panels from the rear door frame forward under the pilots’ and passengers’ floorboards at the next maintenance function, 100-hour, or annual inspections. FAA database records indicate over 200 aircraft had the Capstone phase 1 equipment installation under STC2154AK and therefore require inspection.