NTSB Identification: CHI88IA141.
The docket is stored on NTSB microfiche number 39107.
Scheduled 14 CFR
Incident occurred Wednesday, June 22, 1988 in CHICAGO, IL
Probable Cause Approval Date: 06/11/1990
Aircraft: SWEARINGEN SA226-TC, registration: N329BA
Injuries: 6 Uninjured.

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

THE PILOT REPORTED THAT HE FELT A VIBRATIOIN IN THE YOKE DURING THE TAKEOFF GROUND ROLL, AND ELECTED TO ABORT THE TAKEOFF. THE PILOT STATED THAT AS THE AIRCRAFT RETURNED TO THE GATE, THE ELEVATOR CONTROLS 'SEIZED' COMPLETELY. POST-INCIDENT INVESTIGATION REVEALED THAT A BEARING IN THE SAS SERVO MOTOR ASSEMBLY HAD FAILED, ALLOWING THE MOTOR TO SEIZE, AND JAMMING THE ELEVATOR CONTROLS. THE SYSTEM IS DESIGNED WITH A SLIP CLUTCH TO ALLOW SAS ASSEMBLY OVERRIDE WITH A FORCED OF 70 TO 86 POUNDS APPLIED AT THE YOKE. AN OPERATIONAL TEST OF THE CLUTCH INDICATED THAT OVERRIDE WOULD HAVE BEEN POSSIBLE IF THE CIRCUMSTANCES HAD DEMANDED IT. THE MOST RECENT SCHEDULED INSPECTION OF THE SAS ASSEMBLY OCCURRED JUNE 5, 1988, WITH NO NOTED DISCREPENCIES. AN OPERATIONAL FLIGHT TEST OF THE SAS SYSTEM WAS PERFORMED ON JUNE 15, 1988 WITH SATISFACTORY RESULTS.

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

FAILURE OF THE FRONT MOTOR BEARING IN THE SAS SERVO MOTOR ASSEMBLY, AND THE RESULTANT 'JAMMING' OF THE ELEVATOR CONTROL CABLES. THE PILOT ABORTED THE TAKEOFF AS A RESULT OF THE VIBRATION IN THE YOKE.

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