20251017016219A

On October 17, 2025, the aircraft left billings international airport (kbil) at approximately 20:02Z en route to polson airport (8S1). In review of the weather radar, it appears that during the time of the accident, the aircraft was in mixed precipitation, and several airmets were active in the area, including icing and mountain obscuration airmets. All of the following flight information was captured from ADS-B, and all aircraft speeds are ground speeds.

At approximately 20:11Z, the aircraft climbed to an approximate altitude of 10,000 ft mean sea level (MSL). At 20:45Z, the aircraft was recorded above 12,500 ft MSL and remained above 12,500 ft MSL until approximately 21:17Z, including a period from 20:45Z to 21:17Z where the aircraft was recorded to be above 14,000 ft MSL. From 21:20Z to 21:43Z, the aircraft descended to 12,200 ft MSL. At 21:35Z, the pilot requested to climb to 14,000 ft MSL to avoid icing. The pilot reported the aircraft had previously accumulated light rime ice and wanted to stay out of icing conditions. At 21:43Z, the aircraft climbed through 12,500 ft MSL, and at 21:45Z, it requested to remain at 13,000 ft MSL, stating the aircraft was on top of the weather. During this time, the aircraft’s speed dropped below 70 knots (kt) ground speed (gs), down to approximately 61 kt gs, before leveling out at 13,200 ft MSL.

From 21:50Z to 22:09Z, the recorded ground speeds of the aircraft fluctuated from 85 kt to 129 kt. It’s unclear if icing conditions or wind gusts were the cause of the inconsistent ground speeds during this phase of flight. The aircraft remained at approximately 13,200 ft MSL until 22:09Z. During this time, the pilot coordinated with ATC initially for the RNAV to runway 36 in polson, starting at cabli, and was cleared direct to that initial fix. The pilot stated the weather for ronan had been obtained and requested the visual to 8S1. At 22:08Z, the pilot was cleared direct to 8S1 and assigned to descend to 12,000 ft MSL. During this time, the aircraft’s ground speed continued to fluctuate. At 22:10Z, at an altitude of 12,300 ft MSL, the aircraft was recorded at 85 kt gs. At 22:11Z, the aircraft was at 11,900 ft MSL, down to 11,300 ft MSL, with a ground speed as low as 73 kt recorded.

At 22:12Z, the pilot declared an emergency, stating that the aircraft had engine issues and reported a dive. The pilot requested vectors to lower terrain, and ATC advised the pilot that the minimum vectoring altitude was 10,900 ft MSL. ATC gave the pilot a heading of 185 to head to seeley lake airport. At 22:13Z, the pilot reported intermittent power on the left engine. From 22:13Z to 22:15Z, the aircraft descended from 11,300 ft MSL to 9,900 ft MSL, with ground speeds that ranged from 100 kt to 140 kt. At 22:15Z, the pilot again requested vectors to lower terrain. This was the last transmission before the aircraft dropped off of ATC radar.

On October 28, 2025, the aircraft was transported from the accident site to seeley lake, MT. The inspectors noted that there was no evidence of oxygen use on the aircraft; no oxygen bottles or cannulas were present. The positions of the mixture, propeller control, and throttles were all pulled back, but the propellers did not appear to be feathered. The inspectors observed that the alternate air system was manual and that two alternate air controls were in the closed position. It was undetermined whether the aircraft had an alternate static port or pitot heat due to the extent of damage.

Sas: NM05202600467