Narrative:

Caribbean flight en route to sju. Aircraft was too heavy to climb to FL370 and FL290 was only other available altitude en route on widebody transport X. First 2 hours of flight encountered a very smooth ride without any necessary deviations for adverse WX. At approximately PM00Z, I visually could see some cumulus tops out on the horizon which prompted me to turn on radar set. WX appears to hug close to centerline of airway approximately 100-110 NM ahead of aircraft present position. The returns become more distinctive as we get about 20 NM further south. I turned on the seat belt sign although we're still in calm air. I then built in a 13 NM westerly (R13) deviation line to judge how much maneuverability we would need to evade the returns with the most potent feedback. 13 NM was more than needed. I then relinquished control of aircraft to the captain and went into the forward lav to relieve myself. Upon exiting the lav, I informed the first class flight attendant that I felt it may get rough within 10 mins and to please pass the word and ensure the passengers, etc are secure. Time now is XX32Z. Upon return to flight deck I resumed control of aircraft and informed the captain about what precautionary measures I had just taken. He didn't seem to think this WX was anything to be concerned about and I responded that 'I'd rather be safe than sorry.' he concurred with my statement although I felt he thought I was being overly conservative. I began our deviation westerly as the line now encroaching our path of flight. I maneuvered the aircraft as much as 8.0 NM west of track and as little as 4.0 NM. At this time I'm now slowing aircraft to .78 mach for possible turbulence penetration and changing my radar range from 30 NM to 15 NM and also varying the gain switch on radar control panel from 4 clicks down to automatic gain. I'm painting a significant return approximately 15-22 NM to our east with red on color feedback and another return at 1-1:30 position which appears to show moderate precipitation. My strategy was to maneuver the aircraft in a side heading which would have bisected the gap between the 2 returns in the least vulnerable airspaceaccording to my radar. The captain disagreed. He felt the target at 11 O'clock was bigger and to avoid it by greater distance. I stated that I am painting a significant 'fried egg' at the exact course you are asking me to turn to. He disagreed stating that is low and light precipitation, please turn now, I want to avoid the cell to the left by more than this current heading. Doing as instructed, we're now in thin cirrus, IFR, turning on ignition and anti-ice, I rolled aircraft to his preferrential heading. At XX42Z, we transitioned over the area I was concerned about and the aircraft transitioned from smooth air to an abrupt and immediate 300 ft climb in altitude, kicking off the autoplt and continuing the ascent to 29600 ft. I placed my hands and simultaneously announced I had the aircraft. The climb terminated naturally without any manipulation or control force on the yoke column. The aircraft was wing rocking and vibrating noticeably. I began a very gradual descent back to FL290. Captain stated I was right, he should have listened to me and appeared very shaken. I told him to get hold of himself, it happened, relax and start thinking about the people in the cabin. XY43Z aircraft breaks out into clear, smooth air but I continued slowing aircraft for possible turn off airway in opposite direction for bda. I accomplished a stability check and an engine systems check and aircraft was fine. The flight attendants informed us that they had a dozen or so passenger with injuries/lacerations. Ny commercial radio/ny center approved our diversion to bda and I proceeded to fly to bda at fmo, touching down at YY40Z. This incident/accident was partly due in fact to a 25 year employee in left seat, a 7 year employee in right seat who just checked out as captain on another aircraft but was flying this trip due to crew staff shortage. First officer flew one trip with same captain week prior and felt captain was hyperactive authoritarian and not too receptive to first officer input despite first officer having 4 stripes on his uniform. First officer had more time in type of aircraft than captain at time of incident and felt veryconfident in his ability to interpret information coming from the radar set. Being this was the right seaters last trip as an first officer, rather than argue about change of heading for WX, he just stated his preference of evasion technique and figured 'just 2 more days with napoleon.' I regret not being more emphatic and insistent on what I believed to be the best course of action. Suggest both pilots be more cognizant of the CRM principles and how even a compromise in heading selection may have prevented injuries to those passengers who undid their seat belts after the flight attendants did their last compliance check before the turbulent vertical shear. Supplemental information from acn 187683. Another factor is the radar. I believe that I hit the top of swelling cumulus. Used in automatic gain I have often eyeballed cells which did not paint. To use any other gain setting does not give a baseline of constancy on which to judge the returns. Others have a 'pet' setting but no one really knows what they are using.

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Original NASA ASRS Text

Title: PAX INJURIES NOTED AFTER INFLT ENCOUNTER WITH SEVERE TURB DURING A PENETRATION OF TSTM ACTIVITY.

Narrative: CARIBBEAN FLT ENRTE TO SJU. ACFT WAS TOO HVY TO CLB TO FL370 AND FL290 WAS ONLY OTHER AVAILABLE ALT ENRTE ON WDB X. FIRST 2 HRS OF FLT ENCOUNTERED A VERY SMOOTH RIDE WITHOUT ANY NECESSARY DEVS FOR ADVERSE WX. AT APPROX PM00Z, I VISUALLY COULD SEE SOME CUMULUS TOPS OUT ON THE HORIZON WHICH PROMPTED ME TO TURN ON RADAR SET. WX APPEARS TO HUG CLOSE TO CENTERLINE OF AIRWAY APPROX 100-110 NM AHEAD OF ACFT PRESENT POS. THE RETURNS BECOME MORE DISTINCTIVE AS WE GET ABOUT 20 NM FURTHER S. I TURNED ON THE SEAT BELT SIGN ALTHOUGH WE'RE STILL IN CALM AIR. I THEN BUILT IN A 13 NM WESTERLY (R13) DEV LINE TO JUDGE HOW MUCH MANEUVERABILITY WE WOULD NEED TO EVADE THE RETURNS WITH THE MOST POTENT FEEDBACK. 13 NM WAS MORE THAN NEEDED. I THEN RELINQUISHED CTL OF ACFT TO THE CAPT AND WENT INTO THE FORWARD LAV TO RELIEVE MYSELF. UPON EXITING THE LAV, I INFORMED THE FIRST CLASS FLT ATTENDANT THAT I FELT IT MAY GET ROUGH WITHIN 10 MINS AND TO PLEASE PASS THE WORD AND ENSURE THE PAXS, ETC ARE SECURE. TIME NOW IS XX32Z. UPON RETURN TO FLT DECK I RESUMED CTL OF ACFT AND INFORMED THE CAPT ABOUT WHAT PRECAUTIONARY MEASURES I HAD JUST TAKEN. HE DIDN'T SEEM TO THINK THIS WX WAS ANYTHING TO BE CONCERNED ABOUT AND I RESPONDED THAT 'I'D RATHER BE SAFE THAN SORRY.' HE CONCURRED WITH MY STATEMENT ALTHOUGH I FELT HE THOUGHT I WAS BEING OVERLY CONSERVATIVE. I BEGAN OUR DEV WESTERLY AS THE LINE NOW ENCROACHING OUR PATH OF FLT. I MANEUVERED THE ACFT AS MUCH AS 8.0 NM W OF TRACK AND AS LITTLE AS 4.0 NM. AT THIS TIME I'M NOW SLOWING ACFT TO .78 MACH FOR POSSIBLE TURB PENETRATION AND CHANGING MY RADAR RANGE FROM 30 NM TO 15 NM AND ALSO VARYING THE GAIN SWITCH ON RADAR CTL PANEL FROM 4 CLICKS DOWN TO AUTO GAIN. I'M PAINTING A SIGNIFICANT RETURN APPROX 15-22 NM TO OUR E WITH RED ON COLOR FEEDBACK AND ANOTHER RETURN AT 1-1:30 POS WHICH APPEARS TO SHOW MODERATE PRECIPITATION. MY STRATEGY WAS TO MANEUVER THE ACFT IN A SIDE HDG WHICH WOULD HAVE BISECTED THE GAP BTWN THE 2 RETURNS IN THE LEAST VULNERABLE AIRSPACEACCORDING TO MY RADAR. THE CAPT DISAGREED. HE FELT THE TARGET AT 11 O'CLOCK WAS BIGGER AND TO AVOID IT BY GREATER DISTANCE. I STATED THAT I AM PAINTING A SIGNIFICANT 'FRIED EGG' AT THE EXACT COURSE YOU ARE ASKING ME TO TURN TO. HE DISAGREED STATING THAT IS LOW AND LIGHT PRECIPITATION, PLEASE TURN NOW, I WANT TO AVOID THE CELL TO THE L BY MORE THAN THIS CURRENT HDG. DOING AS INSTRUCTED, WE'RE NOW IN THIN CIRRUS, IFR, TURNING ON IGNITION AND ANTI-ICE, I ROLLED ACFT TO HIS PREFERRENTIAL HDG. AT XX42Z, WE TRANSITIONED OVER THE AREA I WAS CONCERNED ABOUT AND THE ACFT TRANSITIONED FROM SMOOTH AIR TO AN ABRUPT AND IMMEDIATE 300 FT CLB IN ALT, KICKING OFF THE AUTOPLT AND CONTINUING THE ASCENT TO 29600 FT. I PLACED MY HANDS AND SIMULTANEOUSLY ANNOUNCED I HAD THE ACFT. THE CLB TERMINATED NATURALLY WITHOUT ANY MANIPULATION OR CTL FORCE ON THE YOKE COLUMN. THE ACFT WAS WING ROCKING AND VIBRATING NOTICEABLY. I BEGAN A VERY GRADUAL DSCNT BACK TO FL290. CAPT STATED I WAS RIGHT, HE SHOULD HAVE LISTENED TO ME AND APPEARED VERY SHAKEN. I TOLD HIM TO GET HOLD OF HIMSELF, IT HAPPENED, RELAX AND START THINKING ABOUT THE PEOPLE IN THE CABIN. XY43Z ACFT BREAKS OUT INTO CLR, SMOOTH AIR BUT I CONTINUED SLOWING ACFT FOR POSSIBLE TURN OFF AIRWAY IN OPPOSITE DIRECTION FOR BDA. I ACCOMPLISHED A STABILITY CHK AND AN ENG SYSTEMS CHK AND ACFT WAS FINE. THE FLT ATTENDANTS INFORMED US THAT THEY HAD A DOZEN OR SO PAX WITH INJURIES/LACERATIONS. NY COMMERCIAL RADIO/NY CENTER APPROVED OUR DIVERSION TO BDA AND I PROCEEDED TO FLY TO BDA AT FMO, TOUCHING DOWN AT YY40Z. THIS INCIDENT/ACCIDENT WAS PARTLY DUE IN FACT TO A 25 YEAR EMPLOYEE IN L SEAT, A 7 YEAR EMPLOYEE IN R SEAT WHO JUST CHKED OUT AS CAPT ON ANOTHER ACFT BUT WAS FLYING THIS TRIP DUE TO CREW STAFF SHORTAGE. FO FLEW ONE TRIP WITH SAME CAPT WEEK PRIOR AND FELT CAPT WAS HYPERACTIVE AUTHORITARIAN AND NOT TOO RECEPTIVE TO FO INPUT DESPITE FO HAVING 4 STRIPES ON HIS UNIFORM. FO HAD MORE TIME IN TYPE OF ACFT THAN CAPT AT TIME OF INCIDENT AND FELT VERYCONFIDENT IN HIS ABILITY TO INTERPRET INFO COMING FROM THE RADAR SET. BEING THIS WAS THE R SEATERS LAST TRIP AS AN FO, RATHER THAN ARGUE ABOUT CHANGE OF HDG FOR WX, HE JUST STATED HIS PREFERENCE OF EVASION TECHNIQUE AND FIGURED 'JUST 2 MORE DAYS WITH NAPOLEON.' I REGRET NOT BEING MORE EMPHATIC AND INSISTENT ON WHAT I BELIEVED TO BE THE BEST COURSE OF ACTION. SUGGEST BOTH PLTS BE MORE COGNIZANT OF THE CRM PRINCIPLES AND HOW EVEN A COMPROMISE IN HDG SELECTION MAY HAVE PREVENTED INJURIES TO THOSE PAXS WHO UNDID THEIR SEAT BELTS AFTER THE FLT ATTENDANTS DID THEIR LAST COMPLIANCE CHK BEFORE THE TURBULENT VERT SHEAR. SUPPLEMENTAL INFO FROM ACN 187683. ANOTHER FACTOR IS THE RADAR. I BELIEVE THAT I HIT THE TOP OF SWELLING CUMULUS. USED IN AUTO GAIN I HAVE OFTEN EYEBALLED CELLS WHICH DID NOT PAINT. TO USE ANY OTHER GAIN SETTING DOES NOT GIVE A BASELINE OF CONSTANCY ON WHICH TO JUDGE THE RETURNS. OTHERS HAVE A 'PET' SETTING BUT NO ONE REALLY KNOWS WHAT THEY ARE USING.

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.