Narrative:

Departing with heavy rain and strong winds; a line of weather was moving through the area; wet runway. Aircraft are departing with reports of occasional moderate turbulence. Departing runway 28L aircraft are given heading 210 or 290 from tower. We were given heading 290. Late on takeoff I told the first officer my flight director is not working. He said his was not either. After lift-off we were in heavy rain IMC and moderate turbulence. At 1000 ft the first officer is trying to get the flight directors to engage; selecting heading; vertical speed; level change the flight directors were not engaging. At 1500 ft we were momentarily VMC but still with moderate turbulence and we requested a 210 heading and 1500 ft to remain VMC and were given clearance from tower to do so. We leveled off and pulled the throttle back and called for flaps up but we had a flap overspeed. Shortly after; we were able to engage the flight director in heading first then altitude hold and it remained working throughout the flight. We notified dispatch of the overspeed and flight director problem and put it in the logbook upon arrival. While losing flight directors during a critical phase of flight in severe weather may not constitute an emergency; it certainly reduces the level of safety. With the option of maintaining VMC; I feel that increased the level of safety during this critical phase of flight. It is unfortunate that I was not able to reduce power and retract flaps fast enough to avoid an overspeed but with the turbulence and thunderstorms and system problem everything happened very quickly.

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Original NASA ASRS Text

Title: A B737-800 crew exceeded flap speeds and deviated from the departure track when distracted by flight director problems during a departure in difficult weather conditions.

Narrative: Departing with heavy rain and strong winds; a line of weather was moving through the area; wet runway. Aircraft are departing with reports of occasional moderate turbulence. Departing Runway 28L aircraft are given heading 210 or 290 from Tower. We were given heading 290. Late on takeoff I told the First Officer my flight director is not working. He said his was not either. After lift-off we were in heavy rain IMC and moderate turbulence. At 1000 FT the First Officer is trying to get the flight directors to engage; selecting heading; vertical speed; level change the flight directors were not engaging. At 1500 FT we were momentarily VMC but still with moderate turbulence and we requested a 210 heading and 1500 FT to remain VMC and were given clearance from Tower to do so. We leveled off and pulled the throttle back and called for flaps up but we had a flap overspeed. Shortly after; we were able to engage the flight director in heading first then altitude hold and it remained working throughout the flight. We notified Dispatch of the overspeed and Flight Director problem and put it in the logbook upon arrival. While losing flight directors during a critical phase of flight in severe weather may not constitute an emergency; it certainly reduces the level of safety. With the option of maintaining VMC; I feel that increased the level of safety during this critical phase of flight. It is unfortunate that I was not able to reduce power and retract flaps fast enough to avoid an overspeed but with the turbulence and thunderstorms and system problem everything happened very quickly.

Data retrieved from NASA's ASRS site as of April 2012 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.