B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Workload
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Human Factors; Procedure; Weather
Many distractions initially in preflight planning and pre block out ground operations due to significant weather issues; system wide company computer outages; maintenance procedures; and runway change. While dealing with maintenance; I happened to note that ATC was reporting wind shear advisories by ground equipment; however no PIREPs and nothing on any ATIS changes. Nevertheless; I elected to use and thoroughly briefed wind shear performance parameters and procedures.Takeoff data calculations dictated flaps 20 setting. Multiple maintenance issues caused well over an hour delay from that discussion until block out. After block out; during before takeoff checklist; First Officer (FO) set flaps 5 rather than flaps 20 out of habit pattern and I checked that flaps were indeed set to 5 without confirming vs the MCDU the required takeoff flap setting. Takeoff was normal at 134 KIAS rotation speed with no wind shear noted. After takeoff; the FO recognized that we used the wrong flap setting. Concerned about a possible tail strike due to the wrong setting (No other indications); he recalculated the takeoff data for the non-wind shear setting of flaps 5 which resulted in a rotation speed of 144 KIAS so our rotation speed was 10 knots slow. I was using the HUD for takeoff and never approached nor exceeded the tail strike advisory cue. Post flight inspection by the crew revealed no tail strike indications.
B757 flight crew selected unplanned flaps setting thereby increasing risk of a tail strike during takeoff. No damage to aircraft occurred.