What happened
After receiving clearance for a localizer approach to the Texarkara Airport, the pilot cancelled his IFR flight plan, stating an intention to proceed under VFR toward Nashville, Arkansas. Shortly after this change, the pilot reported that he had entered clouds and experienced a loss of vacuum. The pilot further indicated that the turn coordinator was inoperative and that he was experiencing the onset of vertigo.
Air traffic control attempted to provide vectors to return the aircraft to Texarkana, but the controller observed that the pilot was struggling to maintain a specific heading. During the flight, the aircraft underwent a structural breakup.
The investigation
Post-accident examination of the wreckage revealed significant structural damage: the left wing spar was found twisted upward and aft, the right wing spar was bent slightly downward and aft, and the vertical stabilizer spar was bent aft.
A laboratory examination of the vacuum pump was conducted, which revealed that the drive shaft had sheared in torsion, the rotor had broken due to overstress, and the vanes were worn. Investigators also noted an inoperative turn coordinator with an electrical impedance of 10,000 ohms, though it could not be determined if this component failed prior to or during the accident flight.