On January 8, 1998, a Cessna 340A (registration N26956) operated by Sierra Aviation, Inc. was involved in an aviation accident near Bethany, OK. Investigators recorded the probable cause as: The pilot's flight into known adverse weather conditions which resulted in an inadvertent stall due to airframe ice. A factor was the icing conditions. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an ILS approach in moderate icing, the pilot cycled deicing boots and extended gear/flaps. Ice accumulated on tip tanks and windshield. Reducing power at flare caused the airplane to drop to the runway.
Weather Briefing and Approach
The pilot received weather briefings that included an airmet for moderate rime and mixed icing conditions from the freezing level at the surface to flight level 180. During the ILS approach descent, the aircraft encountered moderate rime and mixed icing while in clouds. In response, the pilot cycled the deicing boots and extended the landing gear and flaps.
Icing and Aircraft Configuration
Ice accumulated on the tip tanks and the unheated portion of the windshield. The approach airspeed was maintained at blue line (Vmc) plus 10 knots, with a power setting of 23 inches of manifold pressure.
Landing and Touchdown
The aircraft was over the runway at 25 feet above ground level for the landing flare and touchdown. At that point, the pilot reduced the manifold pressure by approximately 2 inches. Subsequently, the airplane "dropped" to the runway.