NTSB Identification: BFO93IA175.
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Scheduled 14 CFR operation of NORTH AMERICAN AIRLINES
Incident occurred Monday, September 13, 1993 in JAMAICA, NY
Probable Cause Approval Date: 10/20/1994
Aircraft: BOEING 757-200ER, registration: N757NA
Injuries: 85 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.

DURING CRUISE FLIGHT, A RUDDER RATIO WARNING LIGHT APPEARED, FOLLOWED BY UNCOMMANDED RIGHT RUDDER MOVEMENT AND LEFT AILERON INPUT. THE AIRPLANE REMAINED UNDER CONTROL AND THE CREW COUNTERACTED THE RUDDER MOVEMENT MANUALLY. THE CAPTAIN ELECTED TO ABORT THE FLIGHT AND LANDED SAFELY AT THE DEPARTURE AIRPORT. THE RUDDER RATIO WARNING WAS DISPLAYED ON TWO SUBSEQUENT FLIGHTS, DESPITE REPEATED ATTEMPTS TO RESOLVE THE DISCREPANCY. AFTER THE FOURTH WARNING WAS DISPLAYED IN ABOUT TWO MONTHS, AN EXAMINATION OF THE LEFT YAW DAMPER MODULE REVEALED A MALFUNCTION IN THE LEFT HYDRAULIC PRESSURE SWITCH. THE UNIT WAS REMOVED AND REPLACED. NO FURTHER INCIDENTS INVOLVING A RUDDER RATIO WARNING WERE REPORTED.

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

THE FAILURE OF THE LEFT HYDRAULIC PRESSURE SWITCH, WHICH CAUSED THE LEFT YAW DAMPER MODULE TO BECOME INOPERATIVE RESULTING IN UNCOMMANDED RUDDER MOVEMENTS DURING FLIGHT.

Full narrative available

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