Incident Description
The pilot reported that during descent to Burbank, California, at approximately 5,000 feet, the airplane was flying at 155-160 miles per hour when it encountered slight turbulence while in a 15-degree left turn. The tail began to flutter. In accordance with the airplane's Pilot Information Manual, the pilot quickly reduced power and smoothly raised the nose. The vibration stopped after about 3 to 5 seconds. The remainder of the approach and landing was uneventful. During the post-flight inspection, the pilot noticed wrinkles in the left ruddervator.
Maintenance History
Review of airplane maintenance records showed that in January 2001, the two rear bulkheads were straightened and redoubled, short cracks dressed, and new relief flanges fabricated and installed. The empennage skins were redoubled. The airplane was painted, flight controls and systems reinstalled, and static control balance performed. Work complied with Raytheon (Beechcraft) Service Bulletin, Advisory Circular, and Beechcraft 35 Shop Manual.
In April 2001, the ruddervators were rebuilt and painted. After painting, the right ruddervator static balance was 17.33 inch-pounds (in-lb), and the left was 17.59 in-lb. Both were within the allowable range of 16.8 to 19.8 in-lb per the Shop Manual.
In February 2009, the fuselage and wings were repainted by the owner, then by a certified mechanic shop. Control surfaces were not painted.
Post-Accident Inspection
After the incident, a mechanic removed and replaced the spars, re-skinned the airplane, installed doublers, and added a doubler to the center forward of the aft rib. The ruddervator balance was checked and found to be "perfect."
The pilot stated he was flying at 155-160 mph when turbulence occurred. The maximum structural cruising speed (Vno/Vc) is 161 mph, and maneuvering speed (Va) is 131 mph. The pilot was above Va but not above Vno, and had no reason to anticipate turbulence.