History of Flight
On September 24, 2018, at 1032 Alaska daylight time, a Cessna U206G airplane, N1738R, impacted mountainous terrain about 13 miles west of Rainy Pass Lodge Airport (6AK) in Rainy Pass, Alaska. The pilot was fatally injured, and the airplane was destroyed. The aircraft was registered to Laughlin Acquisitions LLC and operated by Regal Air as a Title 14 Code of Federal Regulations Part 135 on-demand cargo flight. Marginal visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed Lake Hood Seaplane Base (LHD), Anchorage, at 0930, en route to a private airstrip on the southwest side of the Alaska Range, about 30 miles west of the accident site.
The operator stated that the flight was intended to deliver approximately 400 lbs of lumber to the private airstrip, pick up two passengers, and return to LHD. The Regal Air chief pilot was flying the same route in another company Cessna 206 and departed 16 minutes after the accident pilot. He maintained radio contact with the accident pilot throughout the flight; most communications concerned weather conditions and cloud coverage along the route, including that weather could change rapidly. The chief pilot also heard the accident pilot in radio communication with the owner of Rainy Pass Lodge but could only hear the pilot's side. The chief pilot lost radio contact around 1030 and assumed the accident pilot had entered Rainy Pass and lost line of sight.
The owner of Rainy Pass Lodge stated that he observed the accident airplane fly over his lodge and made radio contact with the pilot. He noted that Long Lake Hills, about 8 miles southeast, was visible and that cloud coverage to the southeast appeared more significant than to the northwest near Rainy Pass, but seemed to be dissipating. When the chief pilot reached Long Lake Hills, he did not feel comfortable continuing due to low clouds and returned to LHD.
The operator tracked the airplane's flight path using Spidertracks and noticed the track stopped at 1031. Review of Spidertracks data revealed multiple altitude changes, with descents as low as 450 ft above ground level (agl). During the final 7 minutes, the airplane's altitude varied between 1,400 ft and 1,900 ft agl, with the final recorded point at 1,000 ft agl and descending. About 30 minutes after the track stopped and the operator could not contact the pilot, an Alert Notice was issued. The Alaska Air National Guard conducted an aerial search, and the wreckage was discovered near the end of a mountain valley on a steep slope about 3.5 miles southwest of Goodman Pass mouth, adjacent to a box canyon.
Personnel Information
The Federal Aviation Administration (FAA) issued the pilot a second-class special issuance medical certificate on October 20, 2017, with the limitation that he must wear corrective lenses. The special issuance was for obstructive sleep apnea, first granted in 2014.
Meteorological Information
The closest weather observation station was at 6AK. At 0848, the human observer reported wind from 160° at 12 knots gusting to 18 knots, visibility 7 miles, scattered clouds at 1,500 ft, overcast layer at 4,000 ft, temperature 5°C, dewpoint 4°C, barometric pressure 29.56 inHg. At 1058, wind from 140° at 10 knots, visibility 7 miles, scattered clouds at 1,200 ft, broken clouds at 2,700 ft, temperature 6°C, dewpoint 5°C, pressure 29.53 inHg.
The Alaska Aviation Weather Unit issued AIRMETs Sierra, Tango, and Zulu at 0724 for instrument flight rules (IFR) conditions and mountain obscuration in clouds and precipitation, moderate turbulence below 12,000 ft and isolated severe turbulence within 8,000 ft agl, and moderate icing between 8,000 ft and FL180 with freezing level between 4,000 and 5,000 ft. The accident site was on the border of forecast areas, valid at the time of the accident.
An area forecast indicated, after 0700, scattered clouds at 500 ft msl, broken ceiling at 1,500 ft msl, overcast at 3,500 ft msl with cloud tops to FL180, and visibility 3 miles in light rain and mist. East of Sparrevohn (including the accident area), isolated ceilings of 3,500 ft msl were expected. East of a line from Sparrevohn to Nikolai (including the accident area), surface winds from the east to southeast at 30 knots with gusts to 45 knots were forecast.
The flying weather chart predicted IFR conditions for the accident site with areas of wind greater than 30 knots, and occasional to continuous moderate turbulence between the surface and 12,000 ft msl.
The chief pilot stated that on the accident day, he and the accident pilot reviewed weather from 0800 until just before departures, including area forecasts and FAA aviation weather camera imagery. They also received text messages about weather at the intended destination. A pilot report relayed around 0815 indicated 30 to 40 knot winds and low visibility. The accident pilot received an update at about 0915 that wind had decreased to 20 knots near his destination, and he departed shortly thereafter. Around 0940 en route, the accident pilot radioed the company requesting a weather camera review and update along his route. The chief pilot stated he elected to take off with the expectation that both pilots would return if weather was unsuitable.
Wreckage and Impact Information
On September 26, the NTSB investigator-in-charge, an FAA inspector, and the Regal Air chief pilot traveled to the accident site via helicopter. The main wreckage was located at about 4,400 ft msl on the east side of a steep, loose rock-covered mountainside, partially covered in snow. The initial impact point, identified by the propeller assembly and cockpit debris, was at about 4,700 ft msl. Mountain tops at the back of the box canyon were about 5,000 ft msl.
First responders reported that the rescue helicopter's rotor wash blew the wreckage off its perch, causing it to slide down the slope to its final resting point. A debris path of airplane wreckage was found along the slope leading to the main wreckage.
Postaccident examination of the engine and airframe revealed significant impact damage to the leading edges of the wings and the lower fuselage. The propeller assembly had separated from the crankshaft flange; blades exhibited significant leading-edge gouges, chordwise scratches, and curled tips. The engine oil pan was evenly crushed upward into the bottom of the engine. No mechanical malfunctions or anomalies that would have precluded normal operation were found.
The airplane was equipped with an engine data monitor (EDM) recording basic engine parameters. Review of EDM data revealed no anomalies.
Additional Information
The Alaska Air National Guard did not receive a signal from the airplane's emergency locator transmitter (ELT) during the search. During wreckage examination, the ELT showed no significant damage, and the antenna was still connected. The investigation could not determine why the ELT did not transmit.
Medical and Pathological Information
Pilot's sleep apnea report one month before his most recent medical exam (about one year before the accident) showed continuous positive airway pressure (CPAP) usage of 92% for more than 6 hours, with an apnea-hypopnea index of 4.6 (indicating no sleep apnea). The pilot also reported chronic headaches, high blood pressure, and arthritis in the right knee; headaches had improved with CPAP usage.
The Alaska State Medical Examiner's Office performed an autopsy, concluding the cause of death as multiple blunt-force injuries. The autopsy was unremarkable with no signs of natural disease.
Toxicological testing of urine and liver specimens by the FAA Forensic Sciences Laboratory detected an unquantified amount of diphenhydramine (a sedating antihistamine). Propranolol (a non-sedating medication for high blood pressure and migraines) was detected in liver tissue. Acetaminophen and salicylate (found in aspirin) were detected in urine. Blood was not available for testing.