NTSB Identification: CHI96IA109.
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Scheduled 14 CFR NORTHWEST AIRLINES
Incident occurred Monday, March 18, 1996 in DETROIT, MI
Probable Cause Approval Date: 04/24/1998
Aircraft: Airbus Industrie A320-211, registration: N340NW
Injuries: 110 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 captain reported that the crew leveled at flight level 370 and received an elevator aileron computer (ELAC) number two pitch fault message. The message cleared itself. A few minutes later they received servo fault message. The 'pitch jumped +/- 100 feet.' The crew descended to flight level 350. During the level off they received an ELAC number one pitch fault message. The crew declared an emergency and landed uneventfully. The aircraft maintenance log revealed a similar occurrence on the previous flight. Investigation revealed an intermittent fault in the elevator servo controller electrovalve coil and a defective diode in the electronic module for one of the stabilizer actuators. The defective diode produced an intermittent loss of electrical motor power during transient, closed loop control of the actuator.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: a defective diode in the number two stabilizer actuator that produced an intermittent loss of electrical motor power during transient, closed loop control of the actuator. A factor was the intermittent open circuit in the elevator servo controller electrovalve coil. Full narrative available
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