Page 8 - 207034_Jan19T_FINAL3

A Hair's Breadth
Many pilots don’t realize that an aircraft certificated for flight in icing conditions (sometimes called Flight in Icing Conditions, or FIKI, or simply “known ice” certification) are not designed, safe or legal to operate with impunity in all icing conditions. If the rate of ice accumulation is too great
even “known ice” airplanes are not safe to operate. In areas of lesser ice accumulation known-ice airplanes may enter, but may not remain in icing conditions beyond a defined amount of exposure.
Read this icing accident report from the NTSB:
Approximately 13 minutes after departure, the pilot reported the airplane was accumulating ice. He requested and was cleared to descend from 5000 to 4000 feet MSL. Subsequently, the pilot requested and was cleared to descend to 3000 feet, and to proceed direct to the initial approach fix for the RNAV (GPS) 36 approach for landing at a nearby airport. No distress call or additional ATC communications with the pilot were recorded. The airplane impacted trees and terrain approximately 17 miles south of the airport. Tree deformation, ground scars and craters were consistent with a near vertical impact.
Instrument meteorological conditions (IMC) with low ceilings, reduced visibility, light rain, mist, and drizzle prevailed at the departure airport and along the flight route. The temperature profile in the accident area was +1° Celsius at the surface, -3°C at 3000 feet, and above freezing at 7000-8000 feet. SLD (Supercooled Large Droplet moisture) was likely present in the accident area at and below 5000 feet and produced moderate to severe clear icing on the airframe in the minutes prior to the accident. Propeller blades exhibited physical evidence (blade bending and twisting) consistent with high power (at or near the low pitch/high rpm range) and rotation (symmetrical energy) at impact. No evidence of an in-flight mechanical or flight control malfunction was found that would have rendered the airplane uncontrollable prior to the impact.
The NTSB determined the probable cause of this accident to be: The pilot’s inadvertent flight into severe icing conditions. A contributing factor was the pilot’s inadequate preflight planning.
Two PIREPs (Pilot Reports) from the immediate accident area were filed in the hour before the accident air- plane’s departure. FAA records confirmed the pilot received both of these PIREPs when he briefed and filed for his departure just before his 0918 (local time) departure. At 0838, a Beech Baron 58 at 7,000 feet MSL reported the ceiling during climb out was 1,000 feet overcast with the tops of the overcast at 6,000 feet, temperature 10 degrees
by Thomas P. Turner
6 • TWIN & TURBINE January 2019