2024-12 · NASA ASRS report 2190786
B737 NG flight crew reported the First Officer continuing the takeoff after the Captain's seat rolled back during the takeoff roll at approximately 120 kts.
At approximately 120kts during t/o roll; my seat slid backwards on its track. I took my hands off the thrust levers but did inadvertently hold onto the yoke and pull back slightly..the nose came off the ground..I was able to put it back down as I gave the FO control of the aircraft. He put his hands on the thrust levers also. I was able to put my seat back in position at which point I took control of the throttles again..I made normal PM callouts of V1 and rotate (~157 & 167 kts). The FO remained as PF until ~10;000ft and then we switched roles. It was a startling sequence to both of us.My seat operation was completely normal during taxi-out including setting the parking brake several times before takeoff.I was assigned a XA:00 short call status following a Window of Circadian Low (WOCL) flight the day before. Because of the WOCL flight; crew scheduling was not able/legal to call me until XC:00 on this XA:00 short call which they did. I had declined a request to waive this WOCL--legal to assign protection from scheduling. I had a XB:20 wakeup for the previous pairing the day before the incident. These factors did not affect how we handled the situation but fatigue was present.
Everything about the preflight; pushback; and taxi out was normal and routine. The CA was the pilot flying and I was the pilot monitoring. It was VMC with great visibility; dry; and very light winds (I don't recall the exact speed but it was single digit knots).Initially we were cleared to lineup and wait on runway 28L. We were within a few thousand pounds of MTOGW and configured for a flaps 5; bleeds on; derated thrust takeoff; I don't recall the speeds but I believe V1 was upper 150s and rotate was lower 160s. Once cleared for takeoff; all procedures and callouts were executed appropriately. Shortly after the '100 knots' callout; around 115 to 120 knots; the CA's chair slid all the way back and the CA was unable to keep his hands securely on the controls of the airplane. When sliding back he bumped the control column back slightly; I did not notice any impact to the throttles. The plane started to move slightly right of centerline. In that moment I was ready to either take control of the aircraft or for him to reject the takeoff; and in that moment the CA declared 'YOU HAVE THE AIRCRAFT'. I grabbed the yoke and put my hands on the throttles momentarily as the CA went to pull his seat forward. I gently guided the airplane back to centerline as I observed our airspeed to continue to accelerate at a normal rate. With the CA hastily back in position he took the throttle back from my hand and verbalized 'my throttle' and reiterated that I am the PF and for me to just continue the takeoff and departure and he would assume the PM duties; which I acknowledged and silently agreed in the moment was the most prudent path forward. The CA; now acting as the PM; then made the V1 and ROTATE callouts normally. The rotation; liftoff; and departure were all normal; and we transferred aircraft control back to the CA and I went back to the PM role. The rest of the flight went uneventfully. Once at cruise we discussed the situation to assess what exactly happened and what we might have done better. The CA stated that because he saw me vigilant and ready at the controls; and the fact we were already in the high speed regime and he was not in a safe position to reject the takeoff anyway; that he felt it was best for me to take aircraft control and continue the takeoff. Neither of us were sure if the throttles had been unintentionally; momentarily retarded as the CA slid back; but after I had taken control of the aircraft we agreed that it was accelerating normally although neither of us explicitly verified the takeoff power was set correctly and verbalized it. We agreed that attempting a high speed abort in that situation under the pretense of 'unsafe to fly' would have been a much more dangerous alternative; and although we could have executed the scenario better than we did; we thought we were more correct to do what we did and ultimately successful. The CA repeatedly tested his chair to ensure it was locked in place and could find no issues with his seat; it seemed to be in good working order. We concluded it must just have not been originally locked into a set position and it was in a 'between' position (if that makes sense); and as we accelerated on the takeoff roll; the force was enough to break the friction in the mechanism and send him backward.We called back to the flight attendants and spoke to the lead to inform him what had happened and to see what he had perceived in the back of the aircraft. He stated that he felt a very noticeable 'bump' and in that instant thought that we might have been rejecting the takeoff; but then we clearly didn't and he was curious what was going on and was glad we could inform him. The CA and I agreed that what was perceived as a bump was very likely when the CA knocked back the yoke as he slid backward in his chair.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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