Narrative:

Takeoff conditions: rwy 4L; newark 2 departure; initially capped at 3;000 feet MSL; low ceilings; -rasn; engine anti-ice on; and wind shear warnings reported as +/- 5 kts by aircraft in the vicinity.after being deiced/anti-iced and approaching the hold short position; tower told us of the wind shear activity that was not previously reported on ATIS. We subsequently delayed our takeoff in order to reconfigure the aircraft utilizing wind shear precautions (flaps 20; full thrust; utilization of vr maximum; etc). On takeoff the aircraft initially performed very well considering our weight; resulting in an increased pitch attitude to keep from nearing flaps 20 limit speed. Once VNAV was selected at 818 feet; the system went right into altitude cap and the throttles immediately began to retard towards idle; presumably due to our impending level off at 3;000 feet. At the same time; we were switched to departure; given a subsequent climb to 5;000 feet; and given a westerly heading. The pitch was reduced in order to clean up and a turn to the west was initiated when several things simultaneously happened while still below 3;000 feet: 1. With the throttles near idle and still needing to climb; our airspeed was rapidly decreasing despite our continuing efforts to lower pitch.2. We believe we also encounter a loss shear of about 15 kts.at this point we encountered stick shaker and I shoved the throttles to the firewall. During this time due to my distraction; I overshot my intended heading to the point that we were headed in a southwesterly direction before we could get the aircraft accelerating; cleaned up; and climbing again. Our efforts to correct back to course was initiated before ATC queried us about our heading. Additionally we did lose a little altitude during the recovery process.later near top of climb something similar to this happed where the throttles commanded a speed 20 kts greater than planned as we approached FL320. As VNAV speed attempted to trade airspeed for altitude; VNAV path displayed on our fmas and the throttles again began to retard. Manual intervention was again required to keep the airspeed from getting dangerously slow as we struggled to climb to FL360; another 4;000 feet. At this point we decided to write up the system.lessons learned: although not required; flch instead of VNAV would have been a better option for our full thrust takeoff in a 752 with a planned level off of 3;000 feet.

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Original NASA ASRS Text

Title: B757 flight crew reported speed and heading deviations occurred while departing in wind shear conditions.

Narrative: Takeoff conditions: Rwy 4L; Newark 2 departure; initially capped at 3;000 feet MSL; low ceilings; -RASN; engine anti-ice on; and wind shear warnings reported as +/- 5 kts by aircraft in the vicinity.After being deiced/anti-iced and approaching the hold short position; Tower told us of the wind shear activity that was not previously reported on ATIS. We subsequently delayed our takeoff in order to reconfigure the aircraft utilizing wind shear precautions (flaps 20; full thrust; utilization of VR MAX; etc). On takeoff the aircraft initially performed very well considering our weight; resulting in an increased pitch attitude to keep from nearing flaps 20 limit speed. Once VNAV was selected at 818 feet; the system went right into ALT CAP and the throttles immediately began to retard towards idle; presumably due to our impending level off at 3;000 feet. At the same time; we were switched to departure; given a subsequent climb to 5;000 feet; and given a westerly heading. The pitch was reduced in order to clean up and a turn to the west was initiated when several things simultaneously happened while still below 3;000 feet: 1. With the throttles near idle and still needing to climb; our airspeed was rapidly decreasing despite our continuing efforts to lower pitch.2. We believe we also encounter a loss shear of about 15 kts.At this point we encountered stick shaker and I shoved the throttles to the firewall. During this time due to my distraction; I overshot my intended heading to the point that we were headed in a southwesterly direction before we could get the aircraft accelerating; cleaned up; and climbing again. Our efforts to correct back to course was initiated before ATC queried us about our heading. Additionally we did lose a little altitude during the recovery process.Later near top of climb something similar to this happed where the throttles commanded a speed 20 kts greater than planned as we approached FL320. As VNAV SPEED attempted to trade airspeed for altitude; VNAV PATH displayed on our FMAs and the throttles again began to retard. Manual intervention was again required to keep the airspeed from getting dangerously slow as we struggled to climb to FL360; another 4;000 feet. At this point we decided to write up the system.Lessons learned: although not required; FLCH instead of VNAV would have been a better option for our full thrust takeoff in a 752 with a planned level off of 3;000 feet.

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.