WPR14FA094

The pilot’s continued flight into known light-to-moderate icing conditions over mountainous terrain. Contributing to the accident was the loss of engine power due to induction icing.

The instrument-rated pilot was on a 234-nm instrument flight rules (IFR) cross-country flight over mountainous terrain; instrument meteorological conditions prevailed at the time. During the flight, the pilot notified a controller at the Air Route Traffic Control Center (ARTCC) that the airplane was picking up too much ice and requested to divert to an airport located about 96 miles ahead of his position and to descend to 11,000 feet mean sea level (msl). The controller informed the pilot that he could descend to 12,000 feet msl for terrain clearance. Over the following few minutes, the ARTCC controller notified the pilot several times that he had to maintain an altitude of 12,000 feet or above due to terrain clearance, all of which the pilot acknowledged. Following a low-altitude alert issued by the controller, the pilot stated his altitude was 11,500 feet. Subsequently, the pilot advised the controller that he was having engine problems and needed to go to an airport immediately. When the controller asked the pilot to verify his altitude, the pilot responded that he was at 10,000 feet. The controller then asked the pilot if he was able to climb, and the pilot responded "negative." The controller advised the pilot of an airport that was 24 miles behind his position and asked if he wanted to divert. The pilot responded affirmatively and asked for guidance to the airport. About 1 minute later, the pilot advised the controller that the airplane had "just lost its engine." The controller advised the pilot that the airport was at the pilot's six o'clock position and suggested a heading of 253 degrees, adding that another airport was right below their position. There were no further communications with the accident airplane. Wreckage and impact signatures were found consistent with a wings-level, slightly nose-low descent into trees and terrain. Postaccident examination of the airframe and engine revealed no evidence of any preexisting mechanical malfunction that would have precluded normal operation. Airmen's Meteorological Information (AIRMETs) for IFR and mountain obscuration conditions, low-level wind shear and turbulence, and moderate icing were issued for the flight track area and timeframe. In additional to the AIRMETs, multiple pilot reports included reports of light rime-type icing between 8,000 feet and 13,000 feet throughout the region and National Weather Service data was consistent with the pilot reports and AIRMET that were current at the time. The investigation was unable to determine whether the pilot obtained weather information regarding his planned flight. It is likely that the loss of engine power was due to a combination of structural and induction icing during the continued flight in icing conditions in an airplane that was not certified for flight in icing conditions.

A Garmin GPSMap 396 was recovered from the wreckage and subsequently shipped to the NTSB Vehicle Recorders Laboratory, Washington, DC for further examination. Power was applied to the GPS unit and the data was successfully downloaded. The GPS unit contained 40 recorded sessions from July 13, 2013 to December 1, 2013. Two flights were recorded on November 27, 2013, one from BKE to Butte, Montana, and one returning to BKE. The tracks to and from Butte were predominantly a direct course over mountainous terrain. Review of the track log from the day of the accident depicted a departure from runway 8 at BKE. The flight continued on a southerly course until turning to an easterly course at 1231. The data depicted that the flight leveled off at an altitude of about 13,000 feet, at 1237. The flight continued on an easterly heading with altitudes fluctuating around 13,000 feet and groundspeeds between 200 and 228 knots. At 1244, a decrease in groundspeed was observed while altitude remained about 12,900 feet. For the following 6 minutes, the recorded groundspeed decayed to the slowest recorded groundspeed of 165 knots, however, it then increased to a maximum of 200 knots while the recorded altitude fluctuated between 12,800 and 13,000 feet. The data further depicted that at 1953, a decrease in groundspeed and a descent from an altitude of about 13,000 feet started. The descent continued for about 4 minutes before a climb was initiated from the lowest recorded altitude of 11,591 feet. Throughout the following 2 minutes, the flight ascended to an altitude of about 12,014 feet and groundspeed of 139 knots. The data then depicted a constant descent and fluctuating groundspeeds between 123 knots and 179 knots for about 4 minutes to the end of the recorded GPS data. During the last 2 minutes of recorded GPS data, heading changes to the southeast, northeast, and east were observed. The last recorded GPS position was located about 0.19 miles west of the accident site at an altitude of 7,989 feet, groundspeed of 123 knots, and ground track of 083.5 degrees. For further information, see the Recorders Lab GPS Report and attachments within the public docket for this accident. The Valley County Coroner conducted an autopsy on the pilot on January 17, 2014. The medical examiner determined that the cause of death was "…severe blunt force trauma." The FAA's Civil Aeromedical Institute (CAMI) in Oklahoma City, Oklahoma, performed toxicology tests on the pilot. According to CAMI's report, volatiles, and drugs were tested, and had positive results for 46 (mg/dL, mg/hg) Ethanol detected in Muscle and no Ethanol was detected in Liver A National Transportation Safety Board (NTSB) staff meteorologist prepared a factual report for the area and timeframe surrounding the accident. The National Weather Service (NWS) regional radar mosaic for 1300 depicted a large area of echoes to the north of the accident site and no significant echoes over the accident site or over the McCall area, which was reporting light rain at the time of the image. The NWS Weather Depiction Chart for 1200 depicted an area of IFR conditions by a shaded contour over the Washington and Oregon coasts, and a separate area of eastern Washington and northern Idaho, surrounded by an area of marginal visual flight rules (MVFR) conditions. A second area of MVFR conditions was depicted extending over eastern Oregon, southern Idaho, and into western Wyoming, which included the accident site. Two small areas of IFR conditions were embedded within the region. The closest weather reporting facility to the accident site was from McCall Municipal Airport (MYL), McCall, Idaho, located approximately 27 miles west at an elevation of 5,024 feet and along the immediate route of flight. At 1251, recorded weather conditions were wind from 140 degrees at 11 knots, visibility 9 miles in light rain, ceiling overcast at 2,400 feet above ground level (agl), temperature 2 degrees Celsius (C), dew point 0 degrees C, altimeter 30.04 inches of mercury (Hg), remarks: automated observation system, sea level pressure 1017.9-hPa, hourly precipitation 0.03 inches, temperature 2.2 degrees C, dew point 0 degrees C. The closest upper air sounding or rawinsonde observation (RAOB) was from the NWS Boise (BOI), Idaho, located approximately 90 miles south of the accident site at an elevation of 2,867 feet. The 1700 sounding depicted a surface based temperature inversion to 1,500 feet agl with the lifted condensation level (LCL) immediately above at 1,914 feet agl (4,781 feet msl), and a convective condensation level (CCL) 7 at 4,988 feet agl (7,855 feet msl). The expected top of the clouds was at 13,465 feet. The freezing level was identified at 8,455 feet with the sounding indicating a relative humidity greater than 80 percent from 8,000 to 12,000 feet, with temperatures below freezing that supported icing conditions. At the accident airplane cruising level of 13,000 feet the wind was from 300 degrees at 53 knots with a temperature of -8.5 degrees C, with a potential for trace of rime type icing. The icing potential increased at lower levels and reached a 77% probability of moderate clear type icing at 8,500 feet. Between 12,000 and 11,000 feet there was an approximately 80% probability of light clear icing with relative humidity of 95 percent and temperatures between -7 degrees and -5 degrees C. The Geostationary Operational Environmental Satellite number 15 (GOES-15) satellite image for 1300 depicted several bands of low, mid, and high clouds over the area. The radiative cloud top temperature over the last radar target was -59.16 degrees C, which corresponded to cloud tops near 35,000 feet and indicated cirrostratus clouds. Several lenticular cloud bands were also observed supporting mountain wave activity over Oregon, southern Idaho, and northern Nevada, with overcast clouds over the accident site. There were 6 pilot reports of light to moderate rime icing conditions below 18,000 feet scattered over Idaho prior to the accident, and 9 reports after the time of the accident. There were also several reports of mountain wave activity and of light to moderate turbulence at altitudes above 18,000 feet. After the time of the accident there were also 2 urgent pilot reports from aircraft reporting moderate to severe turbulence in the vicinity of Idaho Falls over southern Idaho. A full series of Airmen's Meteorological Information (AIRMETs) issued by the NWS were current for the timeframe and intended route of flight. The active AIRMETS included AIRMET Zulu for moderate icing, AIRMET Sierra for mountain obscuration and AIRMET Tango for low-level windshear and turbulence. The pilot of N36ML logged on to the Direct Users Access Terminal System (DUATS) and filed an instrument flight plan at 1200 on December 1 with a requested altitude of 13,000 feet. No formal weather briefing information was requested on the DUATS system and there was no record of any contact with the FAA contract Flight Service Station. It is unknown if the pilot utilized any additional sources of weather prior to the flight. For further information, see the weather study report within the public docket for this accident. Examination of the accident site by representatives of Textron Aviation under the supervision of the NTSB IIC revealed the airplane impacted terrain about 1.6 miles northwest of the Johnson Creek Airport (3U2) at an altitude of about 7,619 feet msl. The initial point of contact was identified by a group of about 5 topped trees, about 40 feet in height. A swath of 7 topped trees, each reduced in height as the debris path progressed on a heading of about 078 degrees magnetic. Portions of right and left wing, and tail cone were observed within the swatch of topped trees. The aft portion of the fuselage, vertical stabilizer, rudder, and elevators were located about 104 feet from the initial point of contact. A large impact crater w