Narrative:

We were asked to taxi into position and hold, to be ready for immediate takeoff. As we rolled onto the centerline, I released control to the first officer, who would make the takeoff. He advanced the power levers slightly to spool the engines. The tower cleared us for takeoff, so the first officer punched the toga buttons and the autothrottles moved toward takeoff thrust. At the same time the aircraft began to yaw severely to the left. We corrected to the right, but there was a very loud noise and vibration at the same time. As ctlability decreased and the vibration increased, I assumed control of the airplane, closed the power levers and began braking to reject the takeoff. I don't think our speed got much above 20-25 KTS. The noise and vibration continued until the engines spooled down and we were stopped. We taxied clear of the runway and returned to the gate where maintenance found scrubbing on the nose tires and determined they needed to be changed. We were given another airplane and continued our pattern. I was not surprised to hear of nose wheel scrubbing due to the yawing motion of the aircraft. My questions were what caused: 1) the yaw, 2) the noise, and 3) the vibration? I have thought that possibly the engines did not spool up evenly, and on a wet runway, that began to skid the nose wheels. I am writing to you so hopefully, along with other data, we can all learn how to better manage the cfm engines and be wary of: 1) wet runways, 2) immediate takeoff clrncs, and 3) the use of autothrottle in conjunction with engines that may or may not spool up evenly. Company procedure calls for setting approximately 40% N1 before going to takeoff thrust to allow for uneven engine spool prior to setting takeoff. This usually works, however it does not totally eliminate the problem of uneven power on takeoff. It seems, at this point, to be simply a characteristic of these engines. Callback conversation with reporter revealed the following: reporter states: rudder trim was centered. Rudder on this aircraft has approximately 30% effect on the nose wheel. With full rudder the nose wheel turns that direction approximately 30%. As the aircraft started left, both first officer and I fed in full right rudder--this may have caused the nose wheels to move right from direction of movement and start the nose wheel scrubbing on the wet pavement.

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Original NASA ASRS Text

Title: TKOF ABORTED IN MLG ACCOUNT VIBRATION.

Narrative: WE WERE ASKED TO TAXI INTO POS AND HOLD, TO BE READY FOR IMMEDIATE TKOF. AS WE ROLLED ONTO THE CENTERLINE, I RELEASED CTL TO THE F/O, WHO WOULD MAKE THE TKOF. HE ADVANCED THE PWR LEVERS SLIGHTLY TO SPOOL THE ENGS. THE TWR CLRED US FOR TKOF, SO THE F/O PUNCHED THE TOGA BUTTONS AND THE AUTOTHROTTLES MOVED TOWARD TKOF THRUST. AT THE SAME TIME THE ACFT BEGAN TO YAW SEVERELY TO THE LEFT. WE CORRECTED TO THE RIGHT, BUT THERE WAS A VERY LOUD NOISE AND VIBRATION AT THE SAME TIME. AS CTLABILITY DECREASED AND THE VIBRATION INCREASED, I ASSUMED CONTROL OF THE AIRPLANE, CLOSED THE PWR LEVERS AND BEGAN BRAKING TO REJECT THE TKOF. I DON'T THINK OUR SPD GOT MUCH ABOVE 20-25 KTS. THE NOISE AND VIBRATION CONTINUED UNTIL THE ENGS SPOOLED DOWN AND WE WERE STOPPED. WE TAXIED CLR OF THE RWY AND RETURNED TO THE GATE WHERE MAINT FOUND SCRUBBING ON THE NOSE TIRES AND DETERMINED THEY NEEDED TO BE CHANGED. WE WERE GIVEN ANOTHER AIRPLANE AND CONTINUED OUR PATTERN. I WAS NOT SURPRISED TO HEAR OF NOSE WHEEL SCRUBBING DUE TO THE YAWING MOTION OF THE ACFT. MY QUESTIONS WERE WHAT CAUSED: 1) THE YAW, 2) THE NOISE, AND 3) THE VIBRATION? I HAVE THOUGHT THAT POSSIBLY THE ENGS DID NOT SPOOL UP EVENLY, AND ON A WET RWY, THAT BEGAN TO SKID THE NOSE WHEELS. I AM WRITING TO YOU SO HOPEFULLY, ALONG WITH OTHER DATA, WE CAN ALL LEARN HOW TO BETTER MANAGE THE CFM ENGS AND BE WARY OF: 1) WET RWYS, 2) IMMEDIATE TKOF CLRNCS, AND 3) THE USE OF AUTOTHROTTLE IN CONJUNCTION WITH ENGS THAT MAY OR MAY NOT SPOOL UP EVENLY. COMPANY PROC CALLS FOR SETTING APPROX 40% N1 BEFORE GOING TO TKOF THRUST TO ALLOW FOR UNEVEN ENG SPOOL PRIOR TO SETTING TKOF. THIS USUALLY WORKS, HOWEVER IT DOES NOT TOTALLY ELIMINATE THE PROB OF UNEVEN PWR ON TKOF. IT SEEMS, AT THIS POINT, TO BE SIMPLY A CHARACTERISTIC OF THESE ENGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES: RUDDER TRIM WAS CENTERED. RUDDER ON THIS ACFT HAS APPROX 30% EFFECT ON THE NOSE WHEEL. WITH FULL RUDDER THE NOSE WHEEL TURNS THAT DIRECTION APPROX 30%. AS THE ACFT STARTED LEFT, BOTH F/O AND I FED IN FULL RIGHT RUDDER--THIS MAY HAVE CAUSED THE NOSE WHEELS TO MOVE RIGHT FROM DIRECTION OF MOVEMENT AND START THE NOSE WHEEL SCRUBBING ON THE WET PAVEMENT.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.