Incident Overview
The pilot reported that the airplane was in a descent in smooth air when a loud noise occurred and the airplane began shaking. The shaking stopped when the pilot pulled back on the yoke and pulled the throttle back. The pilot stated that after the shaking ceased, the airspeed indicator needle was observed passing below 144 mph.
Aircraft Inspection Findings
An inspection of the aircraft revealed damage to the aft fuselage and empennage. All four corners of the F.S. 256.9 bulkhead were cracked. The left and right ruddervator static underbalance was measured; the left and right ruddervators were found to be 20.25 inch pounds. The acceptable limits for ruddervator underbalance are 16.8 to 19.8 inch pounds.
Maintenance History
A review of the airplane's maintenance records indicated that the left and right ruddervators were reskinned on October 23, 1996. At that time, the ruddervators were primed but not painted. The recorded static underbalance for both ruddervators was 19.5 inch pounds. There was no documentation of any maintenance performed on the ruddervators since they were reskinned.
Airworthiness Directive Compliance
Airworthiness Directive (AD) 98-13-02, which placed a speed restriction of 144 miles per hour indicated airspeed on Models 35, A35, B35, and 35R airplanes, had been complied with. The inspection of the airplane confirmed it had the required placard and red line on the airspeed indicator notifying the pilot that the new VNE speed was 144 mph. The VNE speed prior to the AD was 204 mph.