NTSB Identification: CHI07FA046.
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Accident occurred Tuesday, December 26, 2006 in Jasper, TN
Probable Cause Approval Date: 05/28/2008
Aircraft: Rockwell International 114, registration: N55MB
Injuries: 2 Fatal,2 Serious.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The airplane was established at a cruise altitude of 12,000 feet and the pilot did not report any problems during the en route portion of the flight. Upon initial clearance to descend from cruise altitude, the pilot advised the controller that he might have to stay higher due to ice. The pilot was subsequently cleared to 7,000 feet, instead of the initial 4,000 feet. About 15 miles from the destination airport, the pilot was cleared for a Global Positioning System (GPS) approach and instructed to maintain 3,900 feet until reaching the initial approach fix. The pilot subsequently inquired about descending lower and was cleared to 3,600 feet. The pilot commented that the airplane was "picking up some ice here, so we're trying to be real careful." Track data indicated that the airplane continued toward the airport, descending as low as 3,200 feet. However, about 2.25 miles from the airport, the pilot declared a missed approach, stating: "We're picking up too much ice." The flight was cleared to an alternate airport and instructed to climb to 5,000 feet. However, the airplane was unable to climb above 4,500 feet and the pilot reported that the airplane was still picking up ice. The pilot subsequently stated that he was unable to maintain altitude because of "more ice." He requested vectors out of the icing conditions, but the controller was not aware of any area being better regarding icing. The pilot noted he was "losing altitude now pretty good." The pilot selected an intermediate airport that was closer to his present position. The controller cleared the flight as requested and instructed the pilot to maintain 4,000 feet. The pilot replied, "All I can do is 4,000." Track data indicated that the flight was established on an east-southeasterly course, and passed about 0.6 miles south of the intermediate airport. It entered a left turn to a northeast course and passed the airport, apparently intending to return for landing. The airplane impacted trees and terrain about 1.75 miles northeast of the intermediate airport. A witness stated that the airplane came through the treetops, "nose dived into the ground" and spun around, before coming to rest. GPS altitude data revealed a steadily increasing descent rate after reaching 4,500 during the diversion to the alternate. Airmen's Meteorological Information (AIRMET) advisories for moderate icing were in effect. The AIRMET coverage area included the destination and alternate airports. The pilot obtained two pre-flight weather briefings during which he was advised of the AIRMET. Although, the AIRMET was updated after the briefings, the predicted icing intensity and geographical coverage area remained the same. A post accident inspection of the airplane did not reveal any anomalies consistent with a pre-impact failure or malfunction. Several ice fragments, consistent in appearance to rime ice, were observed on the ground at the accident site by initial responders. The fragments exhibited a contour approximately matching the profile of the wing leading edge. The Pilot's Operating Handbook stated that the airplane was not certified for flight into known icing conditions. The handbook advised that in the case of an inadvertent icing encounter, "evasive action should be initiated immediately when icing conditions are first encountered."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's inability to maintain altitude due to excessive airframe ice accretion, resulting in an in-flight collision with trees and terrain. Additional causes were the pilot's continued flight in icing conditions once they had been encountered, and his failure to promptly initiate evasive action in order to exit the icing conditions. A contributing factor was the pilot's pre-flight decision to operate into an area of forecast moderate icing conditions in an aircraft not equipped with in-flight icing protection. Full narrative available
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