Incident Overview
During an instrument flight in instrument meteorological conditions, the pilot reported a vacuum system failure and a pitot-static system malfunction. Despite these failures, the pilot elected to continue the flight.
Flight Sequence
The flight track and altitude were erratic throughout the flight. After 28 minutes, the pilot reported that the airplane was in a dive. Shortly thereafter, the right outboard wing panel, rudder, and horizontal stabilator(s) separated from the airplane in flight.
Examination Findings
Post-accident examination of the airplane revealed that the vacuum pump drive coupling had sheared. The shearing was caused by improper thread treatment—specifically, the use of sealant tape during installation. The airplane was equipped with a standby vacuum system, which at higher altitudes required the pilot to manually spool the system by reducing power then advancing the throttle to maintain vacuum pressure.