B737-300
Flight Crew Last 90 Days 196
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Rejected Takeoff; Flight Crew Became Reoriented
Aircraft; Human Factors
The Captain gave me control of the aircraft as we centered on the runway. I powered up to >40% and hit TO/GA. We received the autopilot disconnect horn and discontinued the takeoff and cleared the runway. We had a child guest in the cockpit during preflight and made the assumption that the child had pushed the autopilot button; which was then disconnected when TO/GA was pushed. Flew to destination where the Captain contacted Dispatch and Maintenance and the Chief on Duty. Told there was no discrepancy. Made an entry in the logbook.
After passing control of the aircraft to the First Officer for his takeoff; he added power and pressed the TO/GA button. The autopilot disconnect horn immediately went off so I took control of the aircraft and we rejected the takeoff at 5 to 10 knots. The horn was silenced by pressing the autopilot disconnect thumb switch. After exiting the runway; we discussed the situation and decided there was no aircraft discrepancy as we could not duplicate the event on the taxiway. My assumption is that the autopilot was inadvertently turned on while on the ground and pushing the TO/GA button disconnected it; therefore the horn. We departed uneventfully. Upon landing; we talked to Dispatch; Maintenance Control; and the Chief Pilot on Duty. It was agreed that even though there was no discrepancy; we should make an entry in the logbook.
B737-300 flight crew experiences an autopilot disconnect horn after the TO/GA button is pushed during takeoff. The takeoff is rejected and troubleshooting indicates that the autopilot must have been engaged at some time during preflight and not detected until the TO/GA button was pushed. A child visitor to the cockpit may have pushed the button during preflight.