Gray, TN, USA
N15L
BEECH A100
The airplane was flying in instrument meteorological conditions at flight level 200 (about 20,000 feet), and a large area of thunderstorm activity was located to the northwest. About 20 miles from the thunderstorm activity, the airplane began to encounter moderate turbulence and severe icing conditions. The pilot deviated to the south; however, the turbulence increased, and the airplane entered an uncommanded left roll and dive. The autopilot disengaged, and the pilot's attitude indicator dropped. The pilot leveled the airplane at an altitude of 8,000 feet and landed without further incident. Subsequent examination revealed that one-third of the outboard left elevator separated in flight and that the empennage was substantially damaged. Meteorological and radar data revealed the airplane entered an area of rapidly intensifying convective activity, which developed along the airplane's flight path, and likely encountered convectively-induced turbulence with a high probability of significant icing. The effect of icing conditions on the initiation of the upset could not be determined; however, airframe structural icing adversely affects an airplane's performance and can result in a loss of control.
On June 15, 2011, about 1405 eastern daylight time, a Beech A100, N15L, operated by Dynamic Avlease Inc., was substantially damaged when it experienced an in-flight upset, while in cruise flight near Gray, Tennessee. The two certificated commercial pilots were not injured. Instrument meteorological conditions (IMC) prevailed and an instrument flight rules flight plan had been filed for the flight that departed Bridgewater Air Park (VBW), Bridgewater, Virginia, destined for Mid-Continent Airport (ICT), Wichita, Kansas. The positioning flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to the flight crew, the airplane was flying in smooth IMC conditions at flight level 200 (20,000 feet mean sea level), with an area of "moderate to heavy to extreme" precipitation located about 30 miles to the northwest. As the airplane approached 20 miles from the weather, it began to experience moderate turbulence and rime ice on the windscreen. The pilot flying deviated course 40-degrees to the south. Turbulence increased further for about 10 seconds, and the airplane then entered an uncommanded left roll and dive. The autopilot disengaged and the pilot's electrically driven attitude indicator tumbled. The flight crew reduced the engine power levers to idle and were able to recover utilizing the copilot's vacuum driven attitude indicator. The airplane was returned to straight and level flight at an altitude of 8,000 feet; however, flight control instability persisted. The flight crew subsequently diverted to Tri-Cities Regional Airport (TRI), Blountville, Tennessee, where the airplane landed without further incident. Subsequent examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the outboard one-third of the left elevator separated in flight, and the outboard right elevator was deformed downward. In addition, the horizontal stabilizer bulkhead frame was fractured and the aft portion of the airframe sustained several areas of deformation. Review of FAA air traffic control information revealed that the flight crew requested an approximate 15 to 20 degree left deviation at 1405:05, which was approved 11 seconds later. Broken transmissions consistent with the in-flight upset began at 1405:50. According to an NTSB Weather Study, satellite imagery and North American Mesoscale model soundings corresponded to cloud-top heights in the accident area of about 32,000 and 36,000 feet; respectively. Weather radar data revealed heavy values of reflectivity west and northwest of the airplane consistent with convective activity, as it approached the area of the in-flight upset. At 1359, reflectivity values in the immediate area of the accident location were scarce and light; however, by 1407, intensification of reflectivity values were observed immediately along the airplane's flight path. By 1412, this area of reflectivity had further intensified in a pattern consistent with developing convection. A three-dimensional projection of reflectivity values at the area of the in-flight upset confirmed significant vertical development in the convective area during the minutes surrounding the accident time. Several convective significant meteorological information (SIGMETs) were issued for the accident region prior to the accident time; however, none were active for the accident location. The flight crew subsequently filed a pilot report pertaining to the in-flight upset, in which the icing conditions were described as "severe clear/rime." [For additional information regarding meteorological conditions, please see the NTSB Weather Study located in the public docket.] The operator reported the pilot's total flight experience as 4,837 hours; which included 1,941 hours in multiengine airplanes, and 87 hours in the same make and model as the accident airplane. The airplane was maintained under a continuous airworthiness inspection program, and had been operated for approximately 16,170 total hours at the time of the accident. With regards to encountering severe icing conditions, the airplane flight manual stated, in part, "...Warning: Severe icing may result from environmental conditions outside of those for which the airplane is certificated." Procedures for exiting severe icing conditions included disengaging the autopilot, after holding the control wheel firmly.
An encounter with convectively-induced turbulence and icing, which resulted in an in-flight upset and a loss of airplane control.
Source: NTSB Aviation Accident Database
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