ATL97LA027

Flutter of the empennage occurred during cruise flight. The pilot immediately reduced engine power, and the flutter subsided. Duration of the flutter was about three seconds. An examination of the empennage disclosed that the bulkhead at fuselage station (FS) 256.9 exhibited cracks at the four corners of the assembly. Also, buckling of the fuselage skin was noted adjacent to the damaged bulkhead. The ruddervators were removed from the airframe and balance checked in accordance with the Bonanza 35 Series Shop Manual. The left and right ruddervators exhibited static underbalance moments (trailing edge heavy) of 23.73 and 22.95 inch-pounds, respectively. According to the service manual, the required static underbalance range is 16.80 to 19.80 inch pounds. Both ruddervators had been reskinned (or replaced) and repainted. An unbroken paint seal around the screws (that attached the counterweights to the ruddervators) indicated that the counterweights had not been removed subsequent to repainting.

On November 27, 1996, at 1600 eastern standard time, a Beech 35, N4523V, experienced the failure of the aft bulkhead in the empennage section of the airframe while at cruise flight near Lafayette, Georgia. The personal flight operated under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial damage. The pilot-in -command ,the pilot/passengers, and the passenger were not injured. The flight departed Lafayette, Georgia, at 1550.

The two pilots reported that ten minutes into the flight they experienced flutter in the aft section of the airframe. The flutter episode last about three seconds. The pilot immediately reduced engine power, and the flutter episode stopped. The pilot elected to return to the airport in Lafayette and landed without incident. The visual examination of the empennage section disclosed that the airframe had sustained structural damage that wrinkled the skin in the vicinity of both ruddervator and stabilizer assemblies.

An examination of the internal structural components of the empennage disclosed that the bulkhead at fuselage station (FS) 256.9 exhibited cracks at the four corners of the assembly. In the immediate vicinity of the damaged bulkhead, there was buckling to the aft fuselage skin. The remainder of the aft portion of the empennage was not damaged, including the ruddervator assemblies.

The ruddervators were removed from the airframe and balance checked in accordance with the Bonanza 35 series Shop Manual. The left and right ruddervators exhibited static underbalance moments of 23.73 and 22.95 inch-pounds respectively. The required static balance range is 16.80 to 19.80 inch pounds. When the screws that attached the counterbalance assemblies to the ruddervator were removed, there was a top coat paint seal that covered the screw heads.

A review of the airframe maintenance logs disclosed that the last ruddervator painting and balancing were accomplished on January 24, 1987. The maintenance log review also failed to disclose the completion of Airworthiness Directive (AD) 94-20-04, that required a balance check of the ruddervator assemblies within the next one hundred hours time-in-service after the effective date of this AD (see attached AD-94-20-04).