Narrative:

During takeoff roll above 100 KTS the electric trim began to trim nose up followed shortly by the aural takeoff warning horn. A rejected takeoff was initiated immediately at approximately 125 KTS. V1 was 152 KTS. Rejected takeoff automatic braking was discontinued at 100 KTS and moderate manual braking used to 1500' remaining, at which time light braking was used to the end of the runway. The aircraft was taxied onto the taxiway and stopped. We contacted ground control and requested the fire department trucks come out and standby the aircraft. The rejected takeoff brake cooling chart was consulted and we were found to be in the probable brake fuse plug melt down zone. Initially the fire department reported all gear ok, but shortly thereafter the #4 tire was reported as deflating followed by the #1 tire. The aircraft engines were shut down. Stairs for deplaning the passenger were requested from company operations. All passenger deplaned onto airport busses west/O incident. We didn't think we were braking hard enough to cause wheel fuses to melt, only outboard wheels deflated. These have streamlining hubcaps on them. Question: at large airports, would it be feasible to have appropriate mobile stairs available for immediate response? Supplemental information from acn 109138: when the trim initially started its run-away, I thought it was an automatic speed trim system adjustment and that it would cease with little actual trim movement. The automatic speed trim system is designed to maintain the aircraft in trim while in-flight at high power settings with the flaps down. My experience has been that it is a nuisance as it often trims the aircraft when trimming is not needed. It seems to me that the system is an overly complicated one, designed to add cost to the aircraft purchase price. I do not know if this system malfunctioned to give us our run-away. I feel, however, that it is probable. Regardless, I feel the system's need should be reviewed with an eye toward its deactivation.

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Original NASA ASRS Text

Title: REPORTER ABORTED TKOF DUE TO TKOF WARNING HORN.

Narrative: DURING TKOF ROLL ABOVE 100 KTS THE ELECTRIC TRIM BEGAN TO TRIM NOSE UP FOLLOWED SHORTLY BY THE AURAL TKOF WARNING HORN. A REJECTED TKOF WAS INITIATED IMMEDIATELY AT APPROX 125 KTS. V1 WAS 152 KTS. RTO AUTO BRAKING WAS DISCONTINUED AT 100 KTS AND MODERATE MANUAL BRAKING USED TO 1500' REMAINING, AT WHICH TIME LIGHT BRAKING WAS USED TO THE END OF THE RWY. THE ACFT WAS TAXIED ONTO THE TXWY AND STOPPED. WE CONTACTED GND CTL AND REQUESTED THE FIRE DEPT TRUCKS COME OUT AND STANDBY THE ACFT. THE REJECTED TKOF BRAKE COOLING CHART WAS CONSULTED AND WE WERE FOUND TO BE IN THE PROBABLE BRAKE FUSE PLUG MELT DOWN ZONE. INITIALLY THE FIRE DEPT RPTED ALL GEAR OK, BUT SHORTLY THEREAFTER THE #4 TIRE WAS RPTED AS DEFLATING FOLLOWED BY THE #1 TIRE. THE ACFT ENGS WERE SHUT DOWN. STAIRS FOR DEPLANING THE PAX WERE REQUESTED FROM COMPANY OPS. ALL PAX DEPLANED ONTO ARPT BUSSES W/O INCIDENT. WE DIDN'T THINK WE WERE BRAKING HARD ENOUGH TO CAUSE WHEEL FUSES TO MELT, ONLY OUTBOARD WHEELS DEFLATED. THESE HAVE STREAMLINING HUBCAPS ON THEM. QUESTION: AT LARGE ARPTS, WOULD IT BE FEASIBLE TO HAVE APPROPRIATE MOBILE STAIRS AVAILABLE FOR IMMEDIATE RESPONSE? SUPPLEMENTAL INFO FROM ACN 109138: WHEN THE TRIM INITIALLY STARTED ITS RUN-AWAY, I THOUGHT IT WAS AN AUTOMATIC SPD TRIM SYS ADJUSTMENT AND THAT IT WOULD CEASE WITH LITTLE ACTUAL TRIM MOVEMENT. THE AUTOMATIC SPD TRIM SYS IS DESIGNED TO MAINTAIN THE ACFT IN TRIM WHILE INFLT AT HIGH PWR SETTINGS WITH THE FLAPS DOWN. MY EXPERIENCE HAS BEEN THAT IT IS A NUISANCE AS IT OFTEN TRIMS THE ACFT WHEN TRIMMING IS NOT NEEDED. IT SEEMS TO ME THAT THE SYS IS AN OVERLY COMPLICATED ONE, DESIGNED TO ADD COST TO THE ACFT PURCHASE PRICE. I DO NOT KNOW IF THIS SYS MALFUNCTIONED TO GIVE US OUR RUN-AWAY. I FEEL, HOWEVER, THAT IT IS PROBABLE. REGARDLESS, I FEEL THE SYSTEM'S NEED SHOULD BE REVIEWED WITH AN EYE TOWARD ITS DEACTIVATION.

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.