Beech B36TC N36ML accident near Yellow Pine, Idaho

Probable cause

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.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for WPR14FA094 for the full record.