A B747 EICAS alerted 'CONFIG STAB' at about 115 KTS on takeoff roll because of the aircraft's light weight and forward trim setting. The Captain deiced to reject the takeoff and found the stabilizer trim at its limit. A tire change was required before the next takeoff.

Narrative

This was the second leg of a charter from ZZZ to ZZZ1 carrying a full load of military personnel. I was the Captain. We had 2 Maintenance personnel and 2 Ramp personnel in addition to our 14 Flight Attendants. We received our final weights and the center of gravity was about 21 percent resulting in a trim setting of approximately 3.5 units. At trim settings this far forward; the 747 will display a second portion of the stabilizer greenband; which is lighter in color. Our trim was set just at the border of the darker section of the band. This often causes a 'STAB GREENBAND' EICAS caution message; but did not today. All normal checklists were accomplished during taxi out and the trim confirmed at 3.5. We were cleared for takeoff. The Tower had cleared a Beechcraft Musketeer to take off in front of us and gave him a turnout to the south. He was drifting left of centerline with the wind and was not starting his turn as we began our takeoff roll. I was concentrating on keeping him in sight as we began the takeoff roll in case there was a flight path conflict after takeoff as we climbed out. This put more of my normal scan outside the airplane. I was the Pilot Flying. Takeoff power was set and the normal 80 KT call was uneventful. Our V1 was 134 and VR was 145 with V2 at 154. Our takeoff weight was approximately 596.0 thousand LBS. I heard the aural warning sound and glanced inside at the upper EICAS screen. I thought I saw a red CONFIG GEAR message on the screen. The aural warning was steady and the EICAS message steady. I glanced at the airspeed indicator and the speed was roughly 10 KTS below V1. The V1 call had not been made by the First Officer. I aborted the takeoff bringing the throttles to idle and selecting reverse thrust. The autobrakes engaged and the airplane began a rapid deceleration. I evaluated the remaining runway; determined we didn't need maximum braking to stop and called for the autobrakes to be turned off while simultaneously reaching for the selector myself. The First Officer got there first and turned off the autobrakes. This occurred between 70 and 90 KTS. The First Officer told the Tower we were aborting and would clear the runway. They asked if we needed assistance and I requested that they roll the fire trucks and we suspected our brakes would be hot. We cleared the runway and stopped on the parallel taxiway. I did not set the parking brake. I held the brakes as gently as possible and after 3 minutes of cooling we shut down the #2 and #3 engine to reduce our thrust. I said I thought I saw CONFIG GEAR but the First Officer said he thought he saw CONFIG STAB. Either message will generate the aural warning; a red warning light and its respective red EICAS message. I looked down at the STAB position indicator and the lighter portion of the greenband had disappeared and only the normal darker portion remained. Our trim setting was right on the edge of the green band. I selected the brake temperatures synoptic on the lower EICAS screen. The temperatures were beginning to rise from zero. Captain asked our weight and the FMC showed 594.5. I guessed our speed at the abort to be about 120-125 KTS based on our V1 and I told him to use the 600.0 weight on the chart. We determined we would have to wait 50 minutes to 1 hour for the brakes to cool. Based on the temperatures and our weight and the numbers; I determined it safe enough to taxi a short distance further down the taxiway and off to a holding area to clear the taxiway for the Tower. The fire trucks followed us; we started the APU; shut down the remaining engines and requested the fire marshal place chocks under the nose gear tires. The fire marshal scanned each wheel and his readings corresponded with our brake temperatures on the screen. The hottest brake was 280 degrees. We observed the brake temperatures and one brake rose to 6 (the scale goes to 9); 3 went to 5; and the rest never went above 4. Peak temperatures did occur as advertised about 15 minutes after the rejected takeoff. We requested stairs from the FBO and when they arrived; our Maintenance personnel went down to check the wheels and tires. The right forward tire on the right body gear was now flat-spotted and frayed and would need changing. I went down and inspected all the tires and concurred with the mechanic's assessment. The brakes were warm but not hot. We requested a belt loader from the FBO and pulled the spare tire we carried and the jack from the flyaway kit in the aft pit. The 2 mechanics and the 2 ramp men changed the tire. By the time the tire was changed; the brakes had all cooled to zero. We surmised that as we approached V1 and the nose began to rise and the strut extended; the lighter portion of the stabilizer greenband disappeared and our trim was set just outside the darker band. This would account for the 'CONFIG STAB' warning. For the next takeoff; the weights and trim came in roughly the same. I directed the First Officer to increase the trim just a bit to get it inside the edge of the darker greenband. He set it at about 3.7 units. During the subsequent takeoff; I also kept a little extra forward pressure on the control column until I started the rotation at VR. I wanted to ensure the nose strut would not extend prematurely. I am very familiar with the issues we have experienced on the B747 at very light weights and low trim settings. The pressure sensor in the nose gear can cause a 'STAB GREENBAND' EICAS message. Aft center of gravities or an over-serviced nose gear strut usually causes this. Our irregular procedure is adequate to deal with these instances when they occur. I had not seen a case where the lighter portion of the greenband would disappear and leave the current trim setting outside the darker greenband. I plan to follow up with engineering and Boeing to see if there have been any other reports of this. The glare on the upper EICAS screen made it difficult to read the warning message clearly. If I had seen 'CONFIG STAB' instead of what I thought I saw (CONFIG GEAR); I may have reacted differently; especially so close to V1 and knowing the STAB trim was at the edge of the normal greenband. The small airplane on climbout ahead of us was a distraction. The steady aural warning and the red EICAS message elevated the severity of the situation and training kicked in; as it should.