Narrative:

While on the takeoff roll, the takeoff warning horn sounded. As the cause could not be immediately determined, the captain aborted the takeoff (though I was the PF, company operations manual calls VOR the captain to retain control of the power levers through takeoff). Pulling off the runway, permission was asked for and received to perform a runup on the ramp to diagnose the problem. During this time, various switches and levers involved with the warning horn were cycled. The warning horn did not sound during the runup, so another takeoff was attempted. The horn sounded again during the takeoff roll, so the takeoff was again aborted, and the aircraft taxied back to the gate for examination by maintenance personnel. During this examination, the ecu mode switch was found to be in the 'norm' position (it must be in the 'top' position for takeoff), the switch was selected to 'top' and the subsequent takeoff and flight were successfully completed. This ecu mode switch is addressed in three checklists: after takeoff (selected to 'norm'), dscnts (selected to 'top') , and originating (selected to 'top'). The originating checklist contains a 'sublist' consisting of various items accomplished as an aircraft is received from another crew (a swap). The positioning of the ecu mode switch is part of this 'sublist'. As we swapped into this aircraft, the required checklists were performed. Our only explanation is that the position of the switch was not 'seen' correctly. Supplemental information from acn 143082. Electronic control unit switch that allows for automatic power up trim of engine in event of failure during takeoff roll. I can only deduce that I must have not noticed the switch position as I did my checks. It was night time and the switch is unlit. Being new to aircraft I just couldn't remember all items that activate horn.

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Original NASA ASRS Text

Title: FLT CREW ABORTED TWO TKOFS BECAUSE OF WARNING HORN, AFTER RETURN TO BLOCKS MAINTENANCE FOUND THE 'ECU' SWITCH IN THE WRONG POSITION FOR TKOF.

Narrative: WHILE ON THE TKOF ROLL, THE TKOF WARNING HORN SOUNDED. AS THE CAUSE COULD NOT BE IMMEDIATELY DETERMINED, THE CAPT ABORTED THE TKOF (THOUGH I WAS THE PF, COMPANY OPS MANUAL CALLS VOR THE CAPT TO RETAIN CTL OF THE PWR LEVERS THROUGH TKOF). PULLING OFF THE RWY, PERMISSION WAS ASKED FOR AND RECEIVED TO PERFORM A RUNUP ON THE RAMP TO DIAGNOSE THE PROB. DURING THIS TIME, VARIOUS SWITCHES AND LEVERS INVOLVED WITH THE WARNING HORN WERE CYCLED. THE WARNING HORN DID NOT SOUND DURING THE RUNUP, SO ANOTHER TKOF WAS ATTEMPTED. THE HORN SOUNDED AGAIN DURING THE TKOF ROLL, SO THE TKOF WAS AGAIN ABORTED, AND THE ACFT TAXIED BACK TO THE GATE FOR EXAMINATION BY MAINT PERSONNEL. DURING THIS EXAMINATION, THE ECU MODE SWITCH WAS FOUND TO BE IN THE 'NORM' POS (IT MUST BE IN THE 'TOP' POS FOR TKOF), THE SWITCH WAS SELECTED TO 'TOP' AND THE SUBSEQUENT TKOF AND FLT WERE SUCCESSFULLY COMPLETED. THIS ECU MODE SWITCH IS ADDRESSED IN THREE CHKLISTS: AFTER TKOF (SELECTED TO 'NORM'), DSCNTS (SELECTED TO 'TOP') , AND ORIGINATING (SELECTED TO 'TOP'). THE ORIGINATING CHKLIST CONTAINS A 'SUBLIST' CONSISTING OF VARIOUS ITEMS ACCOMPLISHED AS AN ACFT IS RECEIVED FROM ANOTHER CREW (A SWAP). THE POSITIONING OF THE ECU MODE SWITCH IS PART OF THIS 'SUBLIST'. AS WE SWAPPED INTO THIS ACFT, THE REQUIRED CHKLISTS WERE PERFORMED. OUR ONLY EXPLANATION IS THAT THE POS OF THE SWITCH WAS NOT 'SEEN' CORRECTLY. SUPPLEMENTAL INFO FROM ACN 143082. ELECTRONIC CTL UNIT SWITCH THAT ALLOWS FOR AUTOMATIC PWR UP TRIM OF ENG IN EVENT OF FAILURE DURING TKOF ROLL. I CAN ONLY DEDUCE THAT I MUST HAVE NOT NOTICED THE SWITCH POS AS I DID MY CHKS. IT WAS NIGHT TIME AND THE SWITCH IS UNLIT. BEING NEW TO ACFT I JUST COULDN'T REMEMBER ALL ITEMS THAT ACTIVATE HORN.

Data retrieved from NASA's ASRS site as of July 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.