B757 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 215; Flight Crew Type 719
Distraction; Situational Awareness; Time Pressure; Workload
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Weather / Turbulence
General None Reported / Taken
Weather; Human Factors
Pushed back on time. Gate hold procedures in effect due to rapidly approaching storms/gust front from North and East. 15 minute delay in moving airplane from push back position. Dispatch advised extensive delays as some departure fixes blocked by weather. Asked Ground Control for sequence and were told 'unknown' so elected to shut down right engine. Less than one minute later; told to taxi 'number 4 for departure'.Began restart of right engine. Observed gusty winds; blowing debris; approaching squall line/gust front and reset TMC (Thrust Management Computer) for TO/GA (Takeoff/Go-around) power. Reprogrammed FMC (Flight Management Computer) V-speeds to use reduced thrust V-speeds with max thrust. After engine start complete; delayed engine start checklist complete; and takeoff checklist complete; briefed windshear precautions and FM (Flight Manual) responses. Discussed use of increased VR. Very time-compressed. Felt some pressure to get out before weather arrived. But all three of us felt we had addressed threat thoroughly via brief and procedures. Asked ATC for full length on Runway 22R. A330 cleared for takeoff. Winds had shifted from ATIS...LLWS (Low Level Wind Shear) advisory with 15 kt gain on final issued to [the A330]. We requested new ATIS to ensure reading winds properly. Observed wind sock. Verified performance in FMC. We knew that we were good to 10 knots TW (tailwind).767 cleared for takeoff. We finished final items. Similar winds as [the A330] but LLWS advisory cancelled. We agreed to keep full thrust; increased VR.Cleared for takeoff. Heard winds from Tower as 330/22G30. Thought we were dealing with mostly crosswind. Observed windsock as we took runway; thought it was showing about 10 knots. Ran engines up while holding brakes to ensure max performance. Released brakes as throttles advanced under autothrottles.Winds were gusty on takeoff roll. Rapid; precise rudder required. Aircraft acceleration normal. Runway Limit weight VR of 165 easily reached. No airspeed hang-up/decay observed. Lifted off with greater than 3;000 feet remaining. Encountered moderate/severe turbulence at 500 feet AGL but airplane had 180+ knots IAS and was climbing rapidly.On climbout; Dispatch informed us that Tower reported winds were 340/22G30 and we took off with a 22 knot TW component. Quick math = 60 degrees off; so gust was 15 knots TW component. Dispatch discussion revealed that those winds were true; and with 13 degrees magnetic variation; we had closer to a 45 degree off wind; yielding a 22 knot TW component. With checklist completion; briefing; and late engine start; we did not hear those winds as being as much of a TW component as they were when examined by a computer.We were watching weather closely; examining performance; updating ACARS; briefing and instituting windshear precautions; but because of task loading; all three of us missed the shift in wind direction and did not re-calculate takeoff performance. The winds shifted from 270 to 340; to 350 in about three minutes; as [other carriers departed]; then we took off.In flight; we requested a new set of runway data messages with our actual meteorology and aircraft parameters. We had sufficient performance available for a 15 knot TW component; which is the FM limit. The aircraft performed well with winds that are reported to have exceeded that limit.The acceptance of the winds by the two aircraft in front of us was a factor in my not examining the wind direction shift more closely. The true vs. magnetic value of winds was a factor. If the reported winds were magnetic; we were OK; but since they were true; we had an exceedance of allowable TW. In the heat of taking the runway; I didn't even consider that detail.
Departing Newark we had gusting winds which we calculated a strong crosswind component and tailwind component around 10 knots. We took wind shear precautions such as using max thrust and the full runway. After airborne we were notified by Dispatch that he believed we departed with a 20 knot tailwind. By our calculations in flight after the event I could not compute a tailwind that was over 15 knots; which would have made us legal. I'm not sure what the dispatcher was using to calculate his numbers.
B757 flight crew reported departing with a tailwind component that exceeded limits; citing time pressure and rapidly changing weather conditions as contributing factors.