Beech 55 N4817M accident near Liberal, Kansas

Probable cause

The pilot's improper decision to fly in an area where moderate icing conditions were forecasted in an airplane that was not certified for such conditions, and in the effort to get out of the icing conditions, his decision to fly below the minimum descent altitude for the localizer approach to the diversion airport resulting in the airplane impacting a power line and terrain. Contributing was the pilot's inadequate preflight planning.

NTSB analysis

The pilot was conducting a personal flight that encountered moderate rime ice while en route to the planned destination airport. The pilot attempted to climb from 5,100 to 8,000 ft to allow for the accreted ice on the airplane to dissipate, but the airplane was unable to climb and entered an uncontrolled descent. The pilot recovered the airplane at an altitude of about 3,500 ft and then diverted to an alternate airport. During the approach to the diversion airport, the pilot attempted to maintain visual flight and requested a vector for the localizer approach to the airport. The air traffic controller was unable to provide those vectors due to the airplane's low altitude. The airplane impacted a power line about 3 miles south of approach end of the intended landing runway.

Postaccident examination of the airframe and engines revealed no preimpact anomalies that would have precluded normal operation of the airplane. The airplane had ice present on the leading edges of the horizontal stabilizer and the right-side window.

The airplane was not certified for flight in icing conditions. The airplane had an alcohol deice system for the left-side windshield and both propellers. However, postaccident examination of the alcohol reservoir revealed that it had not been used for a period of time, and no fluid was found in the lines leading from the reservoir; thus the windshield and propeller deice system was likely inoperable at the time of the accident.

AIRMET Zulu advisories for moderate ice below 10,000 ft were issued by the National Weather Service's Aviation Weather Center and were applicable for the accident airplane's route of flight and the airspace over the pilot's destination, the airport he was diverting to, and the accident location. Leidos Flight Services indicated that it and any third-party vendor that uses the Leidos system had no contact with the accident pilot on the day of the accident. Thus, the pilot would have been unaware of the forecast icing conditions.

The airplane's uncontrolled descent from 5,100 to 3,500 ft was most likely the result of reduced airplane performance from the ice accretion.

The pilot most likely continued to operate at 3,500 ft, which was too low to be vectored for the localizer, because he wanted to avoid reentering icing conditions as indicated by his informing the controller that he had to use his navigation charts to intercept the localizer inbound to the airport, and his telling the controller when queried that he didn't have the airport in sight because he couldn't see through the windshield and would have to get closer. As a result of his effort to get out of the icing conditions, the pilot descended below the minimum descent altitude for the localizer approach and subsequently impacted the powerline.

Text from the NTSB. Open the NTSB docket for CEN19FA029 for the full record.