B737 flight crew reported safely recovering from an upset on initial approach to ORD related to wake turbulence from a preceding aircraft.
Synopsis
B737 flight crew reported safely recovering from an upset on initial approach to ORD related to wake turbulence from a preceding aircraft.
Narrative
While being vectored for the ILS approach to Runway 10C at ORD; and maintaining 4;000 feet on the assigned heading prior to intercepting the localizer; the aircraft experienced an unexpected and abrupt roll movement. The event occurred near the waypoint RRUDA; with a B747 ahead on approach (previously informed by the Controller). The last time I remember; the heavy aircraft was approximately 4 nautical miles in front of us. Suddenly; the aircraft exhibited a noticeable wing drop and a roll the right. Simultaneously; a Roll Command Arrow in red was displayed on the Primary Flight Display. We were momentarily startled but promptly we identified the situation as an upset condition.- We immediately called out 'Upset.'- The Captain who was the pilot flying; took manual control by disconnecting the autopilot and autothrottle.- No pitch input was necessary as the aircraft was in level flight.- Captain countered the roll by applying opposite aileron input to regain wings-level attitude.- Speed and energy state were stable - no thrust adjustments were required.- Once stabilized; automation was re-engaged.- The aircraft continued inbound and intercepted the localizer and glideslope without further issues.
Second reporter narrative
While on radar vectors for an ILS approach to Runway 10C at Chicago O'Hare (ORD); the aircraft was level at 4;000 feet; approaching the waypoint RRUDA; prior to intercepting the localizer.Just before crossing RRUDA; the aircraft experienced an unexpected Upset Condition. A significant roll was observed; reaching approximately 45 degrees of bank; accompanied by a 'Bank Authority' warning.We reacted immediately in accordance with Upset Recovery procedures: 'Upset' was announced verbally; The autopilot was disengaged; The autothrottle was disconnected; The captain (PF) manually recovered the aircraft attitude correctly and within recommended parameters.After stabilized flight was reestablished; the automation was gradually re-engaged; including auto throttle and autopilot.The aircraft then intercepted the ILS for Runway 10C and continued with a normal approach and landing without further events.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.