Narrative:

Aircraft was written up on the previous leg for inoperative vertical speed mode during autopilot use. On departure this leg; tower advised to stay with them for numerous heading changes. Climbing through 1;000 feet AGL; tower advised new heading which we turned to; still in takeoff go around (toga) mode manually flying with autothrottles on; we cleaned aircraft up; continued climb toward 3;000 feet MSL. There were moderate turbulence encounters from there until cruise altitude. Passing 2;500 feet MSL; tower advised us of a new heading which pilot flying (PF) turned to; passing 2;700 feet; tower advised yet another heading and gave new frequency. Passing 2;900 feet; the autothrottles started to retard for the toga speed and altitude acquire que. At 2;950 feet the flight directors started to direct a descent and I noted PF following them I advised 'you are sinking start a climb'. At 2;800 feet we again were in a climb toward 3;000 feet. At 2;900 feet PF engaged autopilot; I noted altitude acquire; cmd B presented autopilot engaged; autothrottles engaged; aircraft overshot 3;000 feet passing 3;100 feet and continued to climb. I advise PF to correct. PF disengaged autopilot and corrected back but not before we reached about 3;275 feet MSL. Back at 3;000 feet; autopilot was engaged with no further issue. ATC did not mention altitude deviation. We both thought this might be related to the previous vertical speed failure writeup; but that was not verified and it appeared the winds there were causing issues with the autothrottles input and FD commands during altitude acquire.

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Original NASA ASRS Text

Title: A B737 Captain reported flight director and autopilot anomalies during altitude capture with an inoperative autoflight mode.

Narrative: Aircraft was written up on the previous leg for inoperative Vertical Speed mode during autopilot use. On departure this leg; Tower advised to stay with them for numerous heading changes. Climbing through 1;000 feet AGL; Tower advised new heading which we turned to; still in Takeoff Go Around (TOGA) mode manually flying with autothrottles on; we cleaned aircraft up; continued climb toward 3;000 feet MSL. There were moderate turbulence encounters from there until cruise altitude. Passing 2;500 feet MSL; Tower advised us of a new heading which Pilot Flying (PF) turned to; passing 2;700 feet; Tower advised yet another heading and gave new frequency. Passing 2;900 feet; the autothrottles started to retard for the TOGA speed and Altitude Acquire Que. At 2;950 feet the flight directors started to direct a descent and I noted PF following them I advised 'you are sinking start a climb'. At 2;800 feet we again were in a climb toward 3;000 feet. At 2;900 feet PF engaged autopilot; I noted Altitude Acquire; CMD B presented autopilot engaged; autothrottles engaged; aircraft overshot 3;000 feet passing 3;100 feet and continued to climb. I advise PF to correct. PF disengaged autopilot and corrected back but not before we reached about 3;275 feet MSL. Back at 3;000 feet; autopilot was engaged with no further issue. ATC did not mention altitude deviation. We both thought this might be related to the previous Vertical Speed failure writeup; but that was not verified and it appeared the winds there were causing issues with the autothrottles input and FD commands during Altitude Acquire.

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.