Incident Overview
A pilot flying an unspecified aircraft cancelled their IFR flight plan after being cleared for the localizer approach to Texarkana Airport, indicating an intention to proceed VFR to Nashville, Arkansas. Shortly thereafter, the pilot reported being in clouds, having lost vacuum pressure, and that the turn coordinator was inoperative. The pilot stated they were on the verge of vertigo.
Controllers's Response
An air traffic controller attempted to vector the pilot back to Texarkana, but noted the pilot was having difficulty maintaining a heading. The aircraft subsequently broke up in flight.
Aircraft Damage
Examination of the wreckage revealed the left wing spar was twisted upward and aft, the right wing spar was bent slightly downward and aft, and the vertical stabilizer spar was bent aft.
Vacuum Pump Examination
Laboratory examination of the vacuum pump determined that the drive shaft had sheared in torsion, the rotor had broken due to overstress, and the vanes were worn. The condition of the pump indicated failure consistent with the reported loss of vacuum.
Turn Coordinator Status
The turn coordinator, which exhibited an electrical impedance of 10,000 ohms, was found to be inoperative. However, investigators could not determine whether the unit had failed prior to the accident flight or during the flight.