Narrative:

First officer was flying aircraft. I (captain) was working the radar and telling first officer what heading to take to avoid buildups. Center previously approved using our own vectoring. We were at 15000' and got into moderate turbulence. I told first officer to make a 30 degree left turn to get out of turbulence. He made a 30 degree left turn, but also about a 30-40 degree bank. I said not so steep a turn, looked up and he was climbing through 15300'. I said, 'look at your altitude.' I pushed forward on the wheel and he said, 'I don't know what's happening.' I took the control at 15500' and descended, at which time the center cleared us to 11000'. We continued our descent. Contributing factors were: 1) first officer disconnected the autoplt. 2) moderate turbulence and moderate rain. 3) one static discharge off the nose of the aircraft. 4) after I took the controls the first officer said, 'I didn't realize the autoplt was in cws. More than one distraction occurring all at once. When back into clear air and still descending I gave the first officer the controls to continue to phl. No further problem, just discussion between the 2 of us. This all took place in about 15 seconds. Supplemental information from acn 93434: it appears that as I rolled the aircraft with cws the altitude hold function was also overridden and the aircraft began to climb. I initially thought it was a result of the turbulence we had begun to encounter, but as the captain called out 'watch your altitude,' and I checked the altitude selected on the MCP, I realized that something was amiss. The aircraft was climbing at approximately 1000 FPM and I could not get it to descend with the descent 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 altitude hold.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of August 2007 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.