Narrative:

I was the pilot monitoring (pm) for takeoff. Shortly after initiating the takeoff roll; my sliding window rolled back. When this happened; the window caught my headset wire and twisted the headset on my head. I turned to check the wire was free; and was then readjusting it; when suddenly my first officer (first officer) asked me something about my window. I was not sure; (due to noise and headset position) but I believe it was something to the effect of if I was closing the window. I responded no. He immediately announced and conducted a rejected takeoff. I was quite surprised he didn't simply continue the takeoff as the window could easily have been closed once safely airborne. Nonetheless; I felt it was prudent; under the circumstances; to simply take control of the aircraft and complete the rejected takeoff. The reject was uneventful; and we cleared the runway as requested by tower. After arriving at a designated stopping point; I reviewed the rejected takeoff procedure in the QRH. We also looked at brake cooling requirements in the [flight computer]. On this note; I asked my first officer (since I did not see it myself) what speed he initiated the reject at. He said 75 knots. I believed it was actually at a slightly higher airspeed; and therefore checked the [flight computer] for speeds of 85 and 90 knots. 85 knots showed 0 brake cooling time required. 90 knots showed nine minutes required; which by then; we had. I then checked minimum takeoff fuel; which was not a problem. I informed dispatch of what had occurred; and of our intention to continue. The reply via ACARS was 'ok.' we re-accomplished both the before push and before takeoff checklists and departed without further incident.preventative measures: two big lessons learned here are as follows: first; I should have announced loudly and clearly 'continue.' yes it was a bit noisy; and my headset was twisted on my head as a result of the window knocking the wire; however; I could easily have communicated in a loud enough voice to be heard. In all honesty; while I am aware that for any anomaly (particularly above 80 knots) this communication is required; due to the distraction with my headset; and the fact it didn't even cross my mind he would decide to reject; I did not say 'continue.' second; I must; in the future; be more 'assertive' when checking my window during pre-flight. As a matter of explanation; I do (and believe I did in this case check the window). However; as I have observed by many; my technique has never been to bang on the handle with the side of my fist. Generally; I have always; (unless it appeared the window was not correctly closed for whatever reason) simply tapped on the handle while visually determining it is closed. In this case; there seemed no visual indication the window was not properly closed; yet it obviously was not completely locked in place. I will be much more cognizant of this possibility in the future and intend to check it by physically grasping the handle and checking to see it is secure in the locked position.

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Original NASA ASRS Text

Title: B737-800 flight crew reported rejecting the takeoff when the Captain's side window opened.

Narrative: I was the Pilot Monitoring (PM) for takeoff. Shortly after initiating the takeoff roll; my sliding window rolled back. When this happened; the window caught my headset wire and twisted the headset on my head. I turned to check the wire was free; and was then readjusting it; when suddenly my First Officer (FO) asked me something about my window. I was not sure; (due to noise and headset position) but I believe it was something to the effect of if I was closing the window. I responded no. He immediately announced and conducted a rejected takeoff. I was quite surprised he didn't simply continue the takeoff as the window could easily have been closed once safely airborne. Nonetheless; I felt it was prudent; under the circumstances; to simply take control of the aircraft and complete the rejected takeoff. The reject was uneventful; and we cleared the runway as requested by Tower. After arriving at a designated stopping point; I reviewed the rejected takeoff procedure in the QRH. We also looked at brake cooling requirements in the [flight computer]. On this note; I asked my FO (since I did not see it myself) what speed he initiated the reject at. He said 75 knots. I believed it was actually at a slightly higher airspeed; and therefore checked the [flight computer] for speeds of 85 and 90 knots. 85 knots showed 0 brake cooling time required. 90 knots showed nine minutes required; which by then; we had. I then checked minimum takeoff fuel; which was not a problem. I informed Dispatch of what had occurred; and of our intention to continue. The reply via ACARS was 'Ok.' We re-accomplished both the Before Push and Before Takeoff Checklists and departed without further incident.Preventative Measures: Two big lessons learned here are as follows: First; I should have announced loudly and clearly 'Continue.' Yes it was a bit noisy; and my headset was twisted on my head as a result of the window knocking the wire; however; I could easily have communicated in a loud enough voice to be heard. In all honesty; while I am aware that for any anomaly (particularly above 80 knots) this communication is required; due to the distraction with my headset; and the fact it didn't even cross my mind he would decide to reject; I did not say 'Continue.' Second; I must; in the future; be more 'assertive' when checking my window during pre-flight. As a matter of explanation; I do (and believe I did in this case check the window). However; as I have observed by many; my technique has never been to bang on the handle with the side of my fist. Generally; I have always; (unless it appeared the window was not correctly closed for whatever reason) simply tapped on the handle while visually determining it is closed. In this case; there seemed no visual indication the window was not properly closed; yet it obviously was not completely locked in place. I will be much more cognizant of this possibility in the future and intend to check it by physically grasping the handle and checking to see it is secure in the locked position.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.