FO LOST POSITIVE CONTROL OF THE ACFT AND CLIMBED ABOVE ASSIGNED ALT.

Narrative

F/O WAS FLYING ACFT. I (CAPT) WAS WORKING THE RADAR AND TELLING F/O WHAT HDG TO TAKE TO AVOID BUILDUPS. CENTER PREVIOUSLY APPROVED USING OUR OWN VECTORING. WE WERE AT 15000' AND GOT INTO MODERATE TURB. I TOLD F/O TO MAKE A 30 DEG LEFT TURN TO GET OUT OF TURB. HE MADE A 30 DEG LEFT TURN; BUT ALSO ABOUT A 30-40 DEG BANK. I SAID NOT SO STEEP A TURN; LOOKED UP AND HE WAS CLBING THROUGH 15300'. I SAID; 'LOOK AT YOUR ALT.' I PUSHED FORWARD ON THE WHEEL AND HE SAID; 'I DON'T KNOW WHAT'S HAPPENING.' I TOOK THE CONTROL AT 15500' AND DSNDED; AT WHICH TIME THE CENTER CLRED US TO 11000'. WE CONTINUED OUR DSCNT. CONTRIBUTING FACTORS WERE: 1) F/O DISCONNECTED THE AUTOPLT. 2) MODERATE TURB AND MODERATE RAIN. 3) ONE STATIC DISCHARGE OFF THE NOSE OF THE ACFT. 4) AFTER I TOOK THE CONTROLS THE F/O SAID; 'I DIDN'T REALIZE THE AUTOPLT WAS IN CWS. MORE THAN ONE DISTR OCCURRING ALL AT ONCE. WHEN BACK INTO CLEAR AIR AND STILL DSNDING I GAVE THE F/O THE CONTROLS TO CONTINUE TO PHL. NO FURTHER PROB; JUST DISCUSSION BTWN THE 2 OF US. THIS ALL TOOK PLACE IN ABOUT 15 SECS. SUPPLEMENTAL INFO FROM ACN 93434: IT APPEARS THAT AS I ROLLED THE ACFT WITH CWS THE ALT HOLD FUNCTION WAS ALSO OVERRIDDEN AND THE ACFT BEGAN TO CLB. I INITIALLY THOUGHT IT WAS A RESULT OF THE TURB WE HAD BEGUN TO ENCOUNTER; BUT AS THE CAPT CALLED OUT 'WATCH YOUR ALT;' AND I CHKED THE ALT SELECTED ON THE MCP; I REALIZED THAT SOMETHING WAS AMISS. THE ACFT WAS CLBING AT APPROX 1000 FPM AND I COULD NOT GET IT TO DSND WITH THE DSCNT MODE OF THE AUTOPLT. AT 15500' I DISCONNECTED THE AUTOPLT BUT JUST BEFORE I DID SO I NOTICED ON THE AUTOPLT ANNUNCIATOR THAT THE PITCH MODE WAS IN CONTROL WHEEL PITCH; NOT ALT HOLD.