Beech F90 N90QL accident near Midland, Texas

Probable cause

The pilot's failure to maintain the recommended airspeed for icing conditions and his subsequent loss of airplane control while flying the airplane under autopilot control in severe icing conditions, contrary to the airplane's handbook. Contributing to the accident was the pilot's failure to divert from an area of severe icing. Also contributing to the accident was the lack of an advisory for potential hazardous icing conditions over the destination area.

NTSB analysis

The pilot obtained a weather briefing for the flight, during which light freezing drizzle was forecast for the proposed time and route. However, no advisories, either before or during the flight, were issued for the potential of hazardous icing conditions.

The pilot stated that he had all of the airplane's deicing equipment on; however, the airplane accumulated moderate to severe airframe icing. The airplane was cleared for a GPS approach to the airport, and the pilot reported that he used the autopilot to fly the airplane to a navigational fix. An air traffic controller saw that the airplane was off course and subsequently canceled the flight's approach clearance. The copilot's window iced up. The flight was then cleared for another approach attempt, during which the pilot's window became "halfway iced up." The controller advised that the airplane appeared to be "about a half mile south of the course" for runway 25. The pilot configured the airplane with approach flaps and extended the landing gear before the final approach fix. The airplane descended under the cloud deck, and the pilot began to look for the runway. The pilot stated when he advanced the throttles, the airplane rolled about 90 degrees to the left. He disengaged the autopilot and attempted to use the yoke to level the airplane. The airplane then rolled about 90 degrees to the right. The pilot was unable to regain airplane control, and the stall warning horn came on seconds before the airplane impacted the ground. The pilot stated that he believed the loss of control was "primarily due to ice."

The pilot stated that he maintained a target airspeed of 120 knots on approach, 100 knots "close to the ground," and was close to 80 knots when the airplane was in the 90-degree right bank. The airplane's recommended minimum airspeed for sustained flight in icing was 140 knots. The airplane's pilot operating handbook (POH) advises pilots to immediately request priority handling from air traffic control to facilitate a route or an altitude change to exit the icing conditions. Additionally, the handbook cautions the pilot that autopilot usage masks tactile cues, which indicate adverse changes in handling characteristics, and that use of the autopilot is prohibited when any specified visual cues exist in icing conditions.

While the National Weather Service (NWS) issued an icing advisory over an area bordering the destination to the north, no NWS icing advisory extended over the area where the accident occurred. While the pilot would have been aware of potential icing from his weather briefings, he may not have expected the hazard due to the absence of an icing advisory over his route. If the pilot relied upon the graphic presentation provided in the icing advisory, which did not extend to his intended route, he may have been led to believe that he could accomplish the flight safely.

Text from the NTSB. Open the NTSB docket for CEN12LA095 for the full record.