Incident Overview
A pilot was descending from 9,500 feet due to weather conditions. While maneuvering around a cloud cell at 8,000 feet, the airplane began to vibrate. The pilot reduced power and rate of descent, then continued to the destination. After a normal landing, the pilot discovered "serious wrinkling" between the fuselage and the empennage.
Postaccident Evaluation
A postaccident evaluation of the airplane found no pre-existing cracking in the engine mounts. Engine vibration analysis results were within limits. Ruddervator balance tests were also within limits.
Airspeed Analysis
Radar data indicated that the airplane's maximum ground-track speed was 185 knots (213 mph). When this was corrected for altitude and winds aloft, the Investigator In Charge determined that the airplane's indicated airspeed should have been approximately 190 mph when it was descending through 8,000 feet.
Pilot's Operating Handbook (POH) Details
The airplane's Pilot's Operating Handbook (POH) states that this speed is in the airspeed indicator's yellow arc, which is between 176 and 202 mph. The POH further states that maximum structural cruising speed (Vno) is 176 mph, and remarks, "Do not exceed this speed except in smooth air and then only with caution."