Narrative:

En route lax-fra at FL330, cleared by ATC from over las to direct green bay VORTAC. Approximately 15 NM east of denver, noted a line of thunderstorms crossing our intended path, distance approximately 100 NM. Approximately 50 NM southwest of line, I began a 90 degree right turn to heading 135 degrees with ATC approval. Flew this heading approximately 75 NM to break in line where other aircraft were successfully penetrating. Began 90 degree left turn to penetrate through break in line of thunderstorms. Passenger had, several mins before, been instructed by cockpit/cabin PA announcement to fasten seat belts, as were flight attendants over cockpit/cabin intercom to put everything away and fasten seat belts, etc. 3/4 way through this 90 degree turn, moderate turbulence commenced and mach dropped off from .84 to .81. Autoplt let aircraft descend 250 ft to maintain mach, then disconnected itself. Captain had been conducting the turn using 'control wheel steering' mode of autoplt in which the autoplt maintains the aircraft's altitude while the pilot manually controls bank angle. Captain took pitch control of aircraft also when altitude hold function disconnected itself, and slowly applied back pressure to arrest descent, not wishing to lose anymore speed in what became then light to moderate turbulence. As a result, then aircraft descended to 450 ft low (32550 ft) before level off and climb back to FL330 was affected. It is assumed that the altitude deviation was noted by ATC although center made no comment. Several passenger were shaken up or slightly injured due to their having failed to fasten their seat belts. 2 flight attendants were also injured. One cut on the ankle by 1 of 2 serving carts that had not been properly stowed in the aft galley area. This type of altitude deviation is not rare to aircraft equipped with 'soft' autoplts that are programmed to sacrifice altitude to maintain mach speed. Flcs must be extremely vigilant and in this case, ready to disconnect them before altdevs become excessive. Cabin crews must be much more vigilant of non cooperation by passenger when the seat belt sign is illuminated, not wishing to awaken or disturb the passenger is no excuse. As for serving carts -- I have always felt that there should be ways to design them to make them less cumbersome and less dangerous aboard passenger aircraft under any kind of flight conditions, not just bad WX. Until they can be, I'd like to see them banned from commercial aircraft.

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Original NASA ASRS Text

Title: WDB ACFT HAS ALTDEV DUE WX, TSTM ACTIVITY.

Narrative: ENRTE LAX-FRA AT FL330, CLRED BY ATC FROM OVER LAS TO DIRECT GREEN BAY VORTAC. APPROX 15 NM E OF DENVER, NOTED A LINE OF TSTMS XING OUR INTENDED PATH, DISTANCE APPROX 100 NM. APPROX 50 NM SW OF LINE, I BEGAN A 90 DEG R TURN TO HDG 135 DEGS WITH ATC APPROVAL. FLEW THIS HDG APPROX 75 NM TO BREAK IN LINE WHERE OTHER ACFT WERE SUCCESSFULLY PENETRATING. BEGAN 90 DEG L TURN TO PENETRATE THROUGH BREAK IN LINE OF TSTMS. PAX HAD, SEVERAL MINS BEFORE, BEEN INSTRUCTED BY COCKPIT/CABIN PA ANNOUNCEMENT TO FASTEN SEAT BELTS, AS WERE FLT ATTENDANTS OVER COCKPIT/CABIN INTERCOM TO PUT EVERYTHING AWAY AND FASTEN SEAT BELTS, ETC. 3/4 WAY THROUGH THIS 90 DEG TURN, MODERATE TURB COMMENCED AND MACH DROPPED OFF FROM .84 TO .81. AUTOPLT LET ACFT DSND 250 FT TO MAINTAIN MACH, THEN DISCONNECTED ITSELF. CAPT HAD BEEN CONDUCTING THE TURN USING 'CTL WHEEL STEERING' MODE OF AUTOPLT IN WHICH THE AUTOPLT MAINTAINS THE ACFT'S ALT WHILE THE PLT MANUALLY CTLS BANK ANGLE. CAPT TOOK PITCH CTL OF ACFT ALSO WHEN ALT HOLD FUNCTION DISCONNECTED ITSELF, AND SLOWLY APPLIED BACK PRESSURE TO ARREST DSCNT, NOT WISHING TO LOSE ANYMORE SPD IN WHAT BECAME THEN LIGHT TO MODERATE TURB. AS A RESULT, THEN ACFT DSNDED TO 450 FT LOW (32550 FT) BEFORE LEVEL OFF AND CLB BACK TO FL330 WAS AFFECTED. IT IS ASSUMED THAT THE ALTDEV WAS NOTED BY ATC ALTHOUGH CTR MADE NO COMMENT. SEVERAL PAX WERE SHAKEN UP OR SLIGHTLY INJURED DUE TO THEIR HAVING FAILED TO FASTEN THEIR SEAT BELTS. 2 FLT ATTENDANTS WERE ALSO INJURED. ONE CUT ON THE ANKLE BY 1 OF 2 SERVING CARTS THAT HAD NOT BEEN PROPERLY STOWED IN THE AFT GALLEY AREA. THIS TYPE OF ALTDEV IS NOT RARE TO ACFT EQUIPPED WITH 'SOFT' AUTOPLTS THAT ARE PROGRAMMED TO SACRIFICE ALT TO MAINTAIN MACH SPD. FLCS MUST BE EXTREMELY VIGILANT AND IN THIS CASE, READY TO DISCONNECT THEM BEFORE ALTDEVS BECOME EXCESSIVE. CABIN CREWS MUST BE MUCH MORE VIGILANT OF NON COOPERATION BY PAX WHEN THE SEAT BELT SIGN IS ILLUMINATED, NOT WISHING TO AWAKEN OR DISTURB THE PAX IS NO EXCUSE. AS FOR SERVING CARTS -- I HAVE ALWAYS FELT THAT THERE SHOULD BE WAYS TO DESIGN THEM TO MAKE THEM LESS CUMBERSOME AND LESS DANGEROUS ABOARD PAX ACFT UNDER ANY KIND OF FLT CONDITIONS, NOT JUST BAD WX. UNTIL THEY CAN BE, I'D LIKE TO SEE THEM BANNED FROM COMMERCIAL ACFT.

Data retrieved from NASA's ASRS site as of July 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.