NTSB Focuses on Cessna 208B Weight as Cause of Crash in Alaska, Killing 10

The aircraft was operated by Bering Air, a charter carrier that offers scheduled service from 32 villages in western Alaska operating out of Nome, Kotzebue, and Unalakleet. 

According to a NTSB preliminary investigation report released Wednesday, weather conditions during the February 6 flight included snow and temperatures conducive to icing.

The aircraft, which was operating as Bering Air Flight 445, was equipped with a TKS system designed to provide ice protection fluid from a tank in the cargo pod to the panels, propeller, and windshield to prevent the accumulation of airframe ice, NTSB said.

According to the pilot's operating handbook (POH) supplement, a minimum indicated airspeed of 95 knots had to be maintained for operations in icing conditions with a fully functional TKS system. In addition, the supplement said that the maximum allowable takeoff gross weight for flight into known or forecast icing conditions is 8,807 pounds.

Investigators said that the aircraft was also equipped with an Aircraft Payload Extender III (APE III) system under Supplemental Type Certificate SA01213SE, which allowed the aircraft to legally operate with a maximum gross takeoff weight of 9,062 pounds. A post-accident examination of the airplane contents, however, indicated that the baggage and cargo weighed approximately 798 pounds. 

Based on that information, combined with the weight of the fuel and TKS, the airplane’s estimated gross takeoff weight at departure was around 9,865 pounds, which was about 1,058 pounds over the maximum takeoff gross weight for flight into known or forecast icing conditions, NTSB said. It was also about 803 pounds over the maximum gross takeoff weight for any flight operation under the APE III flight manual supplement.

The NTSB said it will be conducting a review to determine the aircraft's center of gravity location and if that had a role in the crash.

On the afternoon of February 6, the Caravan departed from Nome Airport (PAOM), destined for Saint Michael Airport (PAMK), where it was scheduled to continue on to Unalakleet Airport (PAUN).

The flight arrived at PAUN and at 2:36 p.m. local time, the pilot contacted Anchorage Air Route Traffic Control Center (ARTCC), reporting that he was on the ground at PAUN and needed an instrument flight rules (IFR) clearance to PAOM. 

The pilot was cleared to PAOM via the EMMMO waypoint intersection and assigned an altitude of 8,000 feet mean sea level (msl). The flight took off at 2:37 p.m., flying west over Norton Sound toward PAOM. At 2:40 p.m., the pilot contacted ARTCC, and the controller advised  that radar contact was established. The flight was estimated to arrive at PAOM about 3:35 p.m.

At approximately 2:49 p.m., the aircraft was in level flight at an altitude of 8,000 feet msl while approximately 20 miles west of PAUN. At 2:56 p.m, the controller cleared the pilot to descend to 6,000 feet msl at the pilot’s discretion. The pilot began the descent at 3:11 p.m. and also advised receiving current weather and airport information at PAOM, which was 50 miles to the west.

Investigators noted that during the descent, the airplane’s airspeed increased from about 150 knots to about 160 knots. At 3:12 p.m., Nome Airport operations advised Nome Alaska Flight Service Station (AFSS) that Runway 10/28 was being closed temporarily for deicing. Nome AFSS then advised Anchorage ARTCC of the 15-minute runway closure to remove ice. At 3:14 p.m., the controller advised the pilot of Flight 455 that the runway at PAOM was closed and expected to reopen in 10-15 minutes.

The controller added that if the pilot wanted to “slow down a little bit” to prevent the flight from arriving before the runway reopened, that would be fine. The pilot acknowledged the information and the aircraft's airspeed began to decrease. At 3:15 p.m., the airplane leveled at 6,000 feet msl and the engine power decreased along with the airspeed, dropping to 110 knots. It then increased to 120 knots a few minutes later.

At about 3:16 p.m., the controller instructed the pilot to descend at the pilot's discretion and maintain 4,000 feet msl. The pilot acknowledged the instructions and the aircraft started down.

About 3:19 p.m., the airplane was level at 4,000 feet msl and the engine power began to gradually increase. The airspeed was about 112 knots and gradually decreasing. At 3:19:35 p.m., the airspeed had dropped to 99 knots and the autopilot disengaged. At 3:20:07 p.m. the controller instructed the pilot to climb and maintain 4,000 feet msl. 

The final ADS-B data point was recorded at 3:20:09 p.m., around 32 miles east of PAOM and about 12 miles offshore over the Norton Sound. At 3:20:18 p.m., the controller transmitted a low altitude alert to the pilot but there was no response.

Approximately 19 seconds later, the airspeed decreased to about 70 knots, and the altitude was about 3,100 feet msl, at which point the data from onboard avionics ceased.

Images of the crash site show an airplane that appears to have pancaked onto an ice floe. A senior NTSB aerospace engineer is expected to conduct a detailed review of the airplane’s performance as part of the investigation, including an evaluation of its center of gravity location.

NTSB's final accident report is expected to be released in the coming months.