B737-300
Flight Crew Last 90 Days 416
Human-Machine Interface; Troubleshooting
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Rejected Takeoff; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed
Aircraft
All checklists/procedures were properly done prior to takeoff. We then aborted the takeoff due to the Takeoff Warning Horn sounding. Horn did not sound until approximately three to five seconds after takeoff power was set (88.4% N1). The Captain aborted takeoff at approximately 75 KIAS and cleared the runway. We ran the rejected takeoff and Takeoff Configuration Warning Horn Checklists and calculated brake cooling. Horn sounded again when Captain did a throttleburst.We discussed possible problems/solutions. He ran the stab trim forward 'about a dot' and redid the throttleburst with no horn. I mentioned that it was still in the green band on my side before he ran it forward; but apparently 'my side' indicated a higher setting (i.e. 5.2 vs. 4.9). The Captain then notified Dispatch and we told ATC we could take off again after the cooling period. We ensured the aircraft was properly reconfigured for takeoff (i.e. rejected takeoff re-selected) and the Captain made several more throttlebursts. The second takeoff was uneventful.
Brake cooling was 16 minutes. A subsequent throttleburst check gave an immediate Takeoff Warning Horn. Flaps were checked at 1; speedbrake handle down detent; and the trim checked in the green at 4.9 units. However; I noticed the First Officer's trim pointer indicated closer to 5.1 units; so I trimmed the First officer's side to 4.9 (Captain's side now 4.8); and moving the thrust lever forward now produced no horn. Had I checked across the center console to view the First Officer's trim pointer I would have set the trim conservatively with the disparate pointer closest to the edge of the green band further towards the center of the green. If the pointers aren't matching; I'd notify Maintenance to recalibrate.
A B737-300 rejected their takeoff upon receipt of a takeoff warning horn determined to be the result of the Captain's trim indication being in the green band; but not the First Officer's. By electing the most conservative of the two displays a subsequent takeoff was uneventful.