Turbulence and Ice Lead To Serious Control Loss

OK... this flight did NOT sound like a good time. But the double combo of increasing turbulence and rime ice led up to a very serious upset that ultimately culminated in structural damage to the airframe. This could have gone a lot worse and the flight crew apparently had their hands full getting this situation under control.

NTSB Identification: ERA11LA344
14 CFR Part 91: General Aviation
Accident occurred Wednesday, June 15, 2011 in Gray, TN
Aircraft: BEECH A100, registration: N15L
Injuries: 2 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

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 14 Code of Federal Regulations Part 91.

According to initial information obtained from the flight crew and the Federal Aviation Administration (FAA), the airplane was flying in smooth IMC conditions at Flight Level 200 (20,000 feet msl), 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 "several seconds of 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, and landed without further incident.

Subsequent examination of the airplane by an 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.

FMI: www.ntsb.gov