B747 flight crew reported engine control system malfunction resulted in engine surging and a rejected takeoff.
Synopsis
B747 flight crew reported engine control system malfunction resulted in engine surging and a rejected takeoff.
Narrative
During the takeoff roll on flight from ZZZZ to ZZZ; while performing my duties as Relief Pilot; I observed abnormal fluctuations in the N1 parameter of engine number 4 when setting takeoff thrust. The N1 was fluctuating between 106% and 96%.In response to this situation; the Captain and First Officer attempted to stabilize the power; but were unsuccessful. The oscillation persisted and was accompanied by a left and right yawing sensation in the aircraft.The Captain executed a Rejected Takeoff (RTO). The aircraft was brought to a stop on the runway and subsequently vacated. We then came to a stop on the taxiway as per ATC instructions.The Engine number 4 EEC (Electronic Engine Control) was in DMI (Deferred Maintenance); when the thrust was set and adjusted to Take off thrust 104.4 that was the assumed temperature power obtained from the OPT (Onboard Performance Tool) (38C) the engine suddenly start to fluctuated between 106 to 96 N1 the Captain executed the RTO prior V1.Document this event in the Aircraft Technical Log.
Second reporter narrative
During take off; I set the thrust to 70% N1 and all the engines in N1's were symmetry. I called for set the thrust; the F/O ( non-flying pilot) started to set the thrust manually. Once the take off was set (105.4% N1) the F/O immediately said that engine 4 was oscillating. He immediately started to adjust the thrust setting on engine 4 again; but the oscillation continued. The oscillation was from 106% N1 to 94% N1. At that moment I did not feel any YAW movement. I thought it was spurious indication. We tried to stabilized the power but it was impossible. The F/O said that engine #4 continued oscillating again. At that moment I felt a strong YAW movement to the right and then to the left. The V1 speed was getting closer and I felt it was unsafe to continue the take off; due to the YAW movement of the aircraft. I made the decision to reject the take off. The auto brakes worked perfectly. F/O called ATC and requested assistance; as per company procedures. Cause: Engine #4 Electronic Engine Control System Suggestion: Better troubleshooting of systems and replace equipment sooner
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.