Air carrier crew reported the auto throttles had disengaged due to an incorrect OAT FMC entry and resulted in an incorrect takeoff power setting and an extended takeoff roll.
Synopsis
Air carrier crew reported the auto throttles had disengaged due to an incorrect OAT FMC entry and resulted in an incorrect takeoff power setting and an extended takeoff roll.
Narrative
While pushing back off the gate ACRS message alert OAT disagree" and "Takeoff Speeds Deleted" was received. There was no annunciation that the Autothrottle disengaged (I assume this is where it happened). I told the Captain that I would just run new numbers after we started the engine.. New numbers came with the same flap setting (15) and airspeeds within 1 knots of V1; Vr and the same V2 as previous takeoff data. The before Takeoff checklist was initiated at the beginning of taxi to Runway XXR.On Runway XXR; Tower cleared us to take off. I was the Pilot Flying. I released the parking brake and set approx 40% thrust. When the engines stabilized; I advanced the throttles to approx 80%; pressed the TOGA button and called "Check Thrust". I noticed that the throttles didn't move as I would have expected and looked over to the instrument panel. The Captain stated thrust set 95.7% (TO data stated 95.6%). I Initially referenced the upper display; which showed a lower setting (approx 85%); but then looked down to the lower instrument display and saw 95.7% and looked back outside to the runway. I remember questioning what I saw to myself but assumed the Captain was looking at the correct % and I was not and that the throttles must have been close to calculated take off thrust when I set them. We crossed the 28s and I saw the Runway XXL edge and overrun approaching. The Captain called rotate and I felt the need to increase my typical rotation rate as we approached the edge and overrun. I made a comment to the Captain about how much runway we used. He then noticed that the Autothrottles were not engaged. He engaged them and an uneventful departure ensued. We then debriefed the incident at Altitude.When we set Takeoff thrust I failed to reference the FMAs (Flight Mode Annunciator) and I fell into a confirmation bias that the Captain was looking at the correct Takeoff Thrust indication. I did not back him up appropriately."
Second reporter narrative
Bottom line -- takeoff power was never set correctly and as a result the takeoff run was longer than it should have been. Details -- after push back very shortly after we started taxiing we received an OAT Disagree" message on the FMC which dumped the takeoff speeds. The FO sent for new takeoff data; printed the new Time Deferral; and accepted the new takeoff data. Flap setting did not change and the V1 and VR speeds changed by 1 knot each. V2 did not change. What we did not notice was that the auto throttle very likely disengaged at that time. Delayed engine start and taxi to Runway XXL at ZZZ were normal. Soon thereafter were were cleared for takeoff on [Runway] XXL. The FO/PF manually brought the power up and pushed TOGA. I believed at the time the the AT (Autothrottles) had advanced the power levers a bit; but the FO later said that he manually advanced them a bit and then called check thrust. I was watching the thrust lever movements and when I checked thrust my eye was drawn to a number that was very close to what the proper N1 should have been; but just a bit low so I advanced the power levers a bit and called thrust set. The critical error on my part was that my eye had been drawn to N2 rather than N1; and the actual N1 value was very likely less than it should have been because of the lack of AT engagement and my error in referencing N2 rather than N1. In retrospect; I noticed that the acceleration was less than typical; but our range of reduced takeoff power settings and variations in weight did not lead me to conclude at the time that the power was not set appropriately. As we progressed toward the end of the runway; both the FO and I noticed that the we were using more runway than expected. I pushed the power up some more and we rotated at Vr to a 6.5 degree pitch angle. I would estimate that we became airborne in the last 1;000 feet of the runway."
More incidents for this aircraft family →
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.