NTSB Identification: ATL91FA067.
The docket is stored on NTSB microfiche number 44826.
14 CFR Part 91: General Aviation
Accident occurred Monday, March 18, 1991 in HAMILTON, NC
Probable Cause Approval Date: 12/15/1992
Aircraft: PIPER PA-28-201T, registration: N2871H
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

THE PILOT REPORTED A VACUUM SYSTEM FAILURE AND A PITOT STATIC SYSTEM MALFUNCTION DURING AN INSTRUMENT FLIGHT UNDER INSTRUMENT WEATHER CONDITIONS, BUT HE ELECTED TO CONTINUE THE FLIGHT. THE FLIGHT TRACK AND ALTITUDE WERE ERRATIC. AFTER 28 MINUTES OF FLIGHT, THE PILOT REPORTED THAT HE WAS IN A DIVE. SUBSEQUENTLY, THE RIGHT OUTBOARD WING PANEL, RUDDER AND HORIZONTAL STABILATOR(S) SEPARATED IN FLIGHT. EXAMINATION OF THE AIRPLANE REVEALED THAT THE VACUUM PUMP DRIVE COUPLING SHEARED BECAUSE OF IMPROPER THREAD TREATMENT (SEALANT TAPE) USED DURING INSTALLATION. THE AIRPLANE WAS EQUIPPED WITH A STANDBY VACUUM SYSTEM, WHICH AT HIGHER ALTITUDES, REQUIRED THAT THE PILOT SPOOL THE SYSTEM (REDUCE POWER THEN ADVANCE THE THROTTLE) TO MAINTAIN VACUUM PRESSURE.

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

THE PILOT'S IMPROPER USE OF EQUIPMENT WHICH AFFECTED THE OPERATION OF THE STANDBY VACUUM PUMP, THE PILOT'S LOSS OF AIRCRAFT CONTROL AFTER EXPERIENCING SPATIAL DISORIENTATION, AND HIS EXCEEDING THE DESIGN STRESS LIMITS OF THE AIRCRAFT. FACTORS RELATED TO THE ACCIDENT WERE: THE MECHANIC'S IMPROPER USE OF THREAD COATING MATERIAL, THE PILOT'S OPERATION OF THE AIRCRAFT WITH A KNOWN MALFUNCTION OF THE PRIMARY VACUUM PUMP, AND THE ADVERSE WEATHER CONDITIONS.

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