Date: 201504
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Rejected Takeoff
Contributing factors: Equipment / Tooling; Aircraft
Primary problem: Aircraft

Narrative: Preflight normal. Pushed off the gate on time. Taxi out normal. Accomplished Flight Attendant (FA) notification; throttle burst; and Before Takeoff Check.  Cleared for takeoff.... Gave throttles to the First Officer (FO) for his takeoff; lined us up on the roll and handed over aircraft control. He pushed up the throttles; I set the final N1s. FO made the comment that the yoke felt different (I had flown the first leg with no control issues; the winds had been blowing on arrival so I just took note of the comment).  At approximately 110 knots we started to hear a weak Takeoff Warning horn. It took a couple of seconds to figure out what it was due to the lack of volume. At this point I elected to abort at approximately 115 knots. The autobrakes immediately kicked in. I started to brake but backed off and let the autobrakes bring us to a stop. The reject was carried out with minimum thrust reversers. The FO alerted Tower and I told the FAs and Passengers to remain seated. The FO stated that he saw the scoreboard showing CW Pitch and Steering and the 'AP A' light was noticed during the reject. I immediately tried to clear the runway because another carrier was landing behind us; and after being sent around they told Tower they did not have the gas for a go-around.  I pushed up the power but we didn't move. We tried many options but in the end it was because the brakes had locked. We were offered and took fire support due to high brake energy. They measured the temperature at 250.... B FA said that he tweaked his back due to the shoulder strap and would be calling scheduling to be replaced.The volume of the Takeoff Warning horn needs to be louder and the outboard armrests need to be lockable in the up position. During the abort I lost my headset and got yanked because the armrest came down and took out the headset. Tough to hear Tower and talk to everyone in the heat of the battle.


Second narrative: Between 100 to 120 knots; I saw the Takeoff Configuration light and heard the associated Warning Horn. The Captain commenced the Rejected Takeoff procedures and the RTO autobrake system engaged. As I checked our airspeed we were quickly decelerating through 80 knots and I noticed the FMA CWS pitch and roll modes were annunciated. The A CMD autopilot light was also illuminated. At no time had I selected the autopilot; and at the gate and the light was extinguished. We came to a stop and noticed the Stab Trim had gone to zero; but was at five at pushback.


Synopsis: B737 flight crew rejected takeoff at approximately 110 knots due to Takeoff Configuration Warning Horn. Volume of the Warning Horn was noted as weak.