Incident Overview
On June 15, 2011, at approximately 1405 eastern daylight time, a Beech A100, registration N15L, operated by Dynamic Avlease Inc., sustained substantial damage following an in-flight upset while in cruise flight near Gray, Tennessee. The two certificated commercial pilots on board were not injured. The aircraft was operating under instrument flight rules in instrument meteorological conditions, and an IFR flight plan had been filed for the positioning flight from Bridgewater Air Park (VBW), Bridgewater, Virginia, to Mid-Continent Airport (ICT), Wichita, Kansas, under Title 14 Code of Federal Regulations Part 91.
Flight Sequence and Recovery
According to the flight crew, the airplane was cruising smoothly at flight level 200 (20,000 feet mean sea level) with an area of precipitation described as "moderate to heavy to extreme" located about 30 miles to the northwest. As the airplane approached within 20 miles of the weather, it encountered moderate turbulence and rime ice on the windscreen. The pilot flying deviated course 40 degrees to the south. Turbulence intensified for about 10 seconds, after which the airplane entered an uncommanded left roll and dive. The autopilot disengaged, and the pilot's electrically driven attitude indicator tumbled. The crew reduced the engine power levers to idle and executed a recovery using the copilot's vacuum-driven attitude indicator. The aircraft returned to straight and level flight at an altitude of 8,000 feet, but flight control instability persisted. The flight crew subsequently diverted to Tri-Cities Regional Airport (TRI) in Blountville, Tennessee, where the airplane landed without further incident.
Weather Conditions
An NTSB Weather Study indicated that satellite imagery and North American Mesoscale model soundings showed cloud-top heights in the accident area of approximately 32,000 to 36,000 feet. Weather radar data revealed heavy reflectivity west and northwest of the airplane, consistent with convective activity as it approached the upset area. At 1359, reflectivity values near the accident location were scarce and light; however, by 1407, intensification was observed along the airplane's flight path, and by 1412, further intensification occurred in a pattern consistent with developing convection. A three-dimensional projection confirmed significant vertical development during the minutes surrounding the accident time. Several convective SIGMETs had been issued for the region before the accident, but none were active for the specific location. The flight crew later filed a pilot report describing the icing conditions as "severe clear/rime."
Aircraft Examination and Damage
A post-incident examination by a Federal Aviation Administration (FAA) inspector revealed that the outboard one-third of the left elevator had separated in flight, and the outboard right elevator was deformed downward. Additionally, the horizontal stabilizer bulkhead frame was fractured, and the aft portion of the airframe sustained several areas of deformation.
Pilot Experience and Maintenance
The operator reported the pilot's total flight experience as 4,837 hours, including 1,941 hours in multiengine airplanes and 87 hours in the same make and model as the accident airplane. The aircraft was maintained under a continuous airworthiness inspection program and had accumulated approximately 16,170 total hours at the time of the incident. The airplane flight manual contained a warning about severe icing and outlined procedures for exiting such conditions, including disengaging the autopilot after holding the control wheel firmly.
ATC Communications
Review of FAA air traffic control information showed 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.