NTSB Identification: LAX94LA259.
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Accident occurred Saturday, June 18, 1994 in SALINAS, CA
Probable Cause Approval Date: 05/10/1995
Aircraft: MASCARI DISCOVERY S-12, registration: N999
Injuries: 1 Serious.

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

THE EXPERIMENTAL HOMEBUILT DISCOVERY S-12 AIRAILE INADVERTENTLY BECAME AIRBORNE DURING HIGH-SPEED TAXI TESTS. THE MECHANIC CONDUCTING THE TAXI TESTS WAS NOT A CERTIFICATED PILOT. HE CONTACTED THE TOWER AND INFORMED THEM OF HIS SUPRISE FLIGHT. WITHIN MOMENTS THE ENGINE FAILED, AND A FORCED LANDING WAS MADE IN A NEARBY FIELD. THE AIRPLANE COLLIDED WITH A STANDPIPE. WITNESSES REPORTED THAT THE PROPELLER, MUFFLER, AND REDUCTION GEARBOX HAD SEPARATED BEFORE THE AIRPLANE STRUCK THE STANDPIPE. EXAMINATION REVEALED THAT THE MUFFLER FRACTURED AT A FACTORY WELD; THE FRACTURE EXHIBITED EVIDENCE OF OXIDATION. THE MUFFLER THEN SEPARATED AS A RESULT OF NORMAL VIBRATION DURING OPERATION OF THE ENGINE. THE PROPELLER WAS DAMAGED AFTER THE MUFFLER STRUCK IT. THE DAMAGED PROPELLER WAS THEN OUT OF BALANCE, RESULTING IN THE REDUCTION GEARBOX SEPARATING FROM THE ENGINE.

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

THE FAILURE OF THE MUFFLER ASSEMBLY DUE TO PREEXISTING CRACKING IN THE OXIDIZED AREA OF THE WELD, WITH SUBSEQUENT DAMAGE AND SEPARATION OF THE PROPELLER AND REDUCTION GEAR BOX. A RELATED FACTOR WAS THE EXCESSIVE TAXISPEED WHICH RESULTED IN THE AIRPLANE BECOMING INADVERTENTLY AIRBORNE.

Full narrative available

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