overspeeding a CF6

[HF8903]

while hoppin cross the pond many moons ago
i saw something i had never really thought about happening..I was on board a 747-200
with autothrottle...the S/O and i where chatting when i looked up to the gauges
and noticed engine 2 N1'ing 107 while the others 100...the engineer hopped out of his seat to set it back. Im curious to know how the engine could creep up like that,it made me think of a dc-10 many years back that had its engine explode while it N1'ed 112...but that was because of a pulled CB. Could the autothrottle need recalibration?

[gas path]

CF6-50 max n1 125% before the engine had to be pulled and 119.5% before maintenance action was necessary (approx 4300 and 4070 rpm!). Auto throttle servo is a linear actuator attached to the throttle clutch pack commanded by the autothrottle computor, the servo drives all 4 T/L together, so if one T/L was displaced relative to the other 3 they would still move together but from the different null points.
That 10 disc failure was due to poor manufacturing process I think.
The difference in N1 could be due to a tired engine or MEC (main engine control)

[This message has been edited by gas path (edited 06 January 2001).]

[HF8903]

Many thanks,so much to learn,so little time!