NTSB Identification: DEN08IA030.
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Incident occurred Saturday, September 22, 2007 in Emporia, KS
Probable Cause Approval Date: 04/30/2008
Aircraft: Beech C90A, registration: N871KS
Injuries: 8 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

While in cruise flight at 12,000 feet mean sea level, the airplane suddenly began "shuddering with a severe high frequency vibration." The pilot stated that the "vibration was in the entire airframe, not specifically the flight controls, so I had no clue where it was coming from." The pilot reduced the power on the left engine; however, the vibration continued. The pilot reduced the power on the right engine, and the vibration stopped. The pilot then shutdown and secured the right engine. Within a couple minutes of securing the right engine, the vibration "returned just as bad as before." The pilot then elected to divert to a nearby airport. The pilot lowered the landing gear during the approach, and the vibration stopped again. The airplane landed uneventfully. During a post flight inspection, the pilot observed the right elevator trim tab push rod was broken. The clevis which connected to the trim tab surface was "pinched due to an overtorqued bolt and nut." Metallurgical examination of the broken rod revealed a fatigue crack that propagated through at least 95 percent of the thread cross section. Maintenance records revealed the right elevator trim tab push-pull tube bolts and bushings were removed and replaced. At the time of the incident, the airframe had accumulated 101.5 flight hours since the inspection, and no additional maintenance to the right elevator trim system was noted in the maintenance records.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

The improper installation of the right elevator trim tab attachment hardware by maintenance personnel which resulted in excessive wear, fatigue, and the failure of the push-pull tube.

Full narrative available

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