Narrative:

We were level at FL310 in cruise portion of flight. WX radar was on and we had been deviating along course throughout the flight due to thunderstorm activity. About 160 mi out, we noted a developing line of trw northwest of memphis, directly along our route of flight. We were in the clear, and as we got closer we discussed options of going between 2 cells or attempting to go around the end of the line of storms. Both visually and on radar it looked as if there was a hole of sufficient size to pass through between 2 cells. We decided on that course of action, but the closer we got, both visually and on radar, the hole began to close as the cells grew together to form a nearly solid line. Just as we entered the cirrus blow off from one of the cells, the captain abandoned the plan to attempt to go between the cells and initiated a sharp turn away from the line of storms (turn reversal of approximately 150 degrees to parallel line of trw). In order to turn more quickly, he disengaged the autoplt and banked sharply (approximately 60 degrees) in order to avoid the cell, get out of the cirrus and get back into the clear. Because of the altitude and steep bank angle used in the turn, we began to lose altitude. The altitude alert warning sounded as we lost altitude, at which time I told the captain to 'roll it out,' and, 'pull it up.' at lowest point just prior to recovery back to a wings level climb, I noted a loss of 700' from assigned altitude (30300' indicated). Center was notified of course change for trw avoidance during the turn. Shortly after leveling off back at FL310, center issued climb instructions to FL330. No mention of or query was made by the center controller of our altitude deviation. Human performance considerations. Both of us failed to recognize the fast rate at which the cells were building and growing together. An earlier decision to abandon our initial plan and opt to go around the line would have avoided the last minute abrupt turn reversal. The captain was very concerned that we not enter the cell, thus the sharpness of the turn used to avoid the area.

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Original NASA ASRS Text

Title: FLT CREW OF MLG AT FL310 MADE AN ABRUPT REVERSAL OF 150 DEGREES TO AVOID OVERHANG OF TRW. ADVISED CENTER AFTER TURN AND ALT RECOVERY.

Narrative: WE WERE LEVEL AT FL310 IN CRUISE PORTION OF FLT. WX RADAR WAS ON AND WE HAD BEEN DEVIATING ALONG COURSE THROUGHOUT THE FLT DUE TO TSTM ACTIVITY. ABOUT 160 MI OUT, WE NOTED A DEVELOPING LINE OF TRW NW OF MEMPHIS, DIRECTLY ALONG OUR RTE OF FLT. WE WERE IN THE CLR, AND AS WE GOT CLOSER WE DISCUSSED OPTIONS OF GOING BTWN 2 CELLS OR ATTEMPTING TO GO AROUND THE END OF THE LINE OF STORMS. BOTH VISUALLY AND ON RADAR IT LOOKED AS IF THERE WAS A HOLE OF SUFFICIENT SIZE TO PASS THROUGH BTWN 2 CELLS. WE DECIDED ON THAT COURSE OF ACTION, BUT THE CLOSER WE GOT, BOTH VISUALLY AND ON RADAR, THE HOLE BEGAN TO CLOSE AS THE CELLS GREW TOGETHER TO FORM A NEARLY SOLID LINE. JUST AS WE ENTERED THE CIRRUS BLOW OFF FROM ONE OF THE CELLS, THE CAPT ABANDONED THE PLAN TO ATTEMPT TO GO BTWN THE CELLS AND INITIATED A SHARP TURN AWAY FROM THE LINE OF STORMS (TURN REVERSAL OF APPROX 150 DEGS TO PARALLEL LINE OF TRW). IN ORDER TO TURN MORE QUICKLY, HE DISENGAGED THE AUTOPLT AND BANKED SHARPLY (APPROX 60 DEGS) IN ORDER TO AVOID THE CELL, GET OUT OF THE CIRRUS AND GET BACK INTO THE CLR. BECAUSE OF THE ALT AND STEEP BANK ANGLE USED IN THE TURN, WE BEGAN TO LOSE ALT. THE ALT ALERT WARNING SOUNDED AS WE LOST ALT, AT WHICH TIME I TOLD THE CAPT TO 'ROLL IT OUT,' AND, 'PULL IT UP.' AT LOWEST POINT JUST PRIOR TO RECOVERY BACK TO A WINGS LEVEL CLB, I NOTED A LOSS OF 700' FROM ASSIGNED ALT (30300' INDICATED). CENTER WAS NOTIFIED OF COURSE CHANGE FOR TRW AVOIDANCE DURING THE TURN. SHORTLY AFTER LEVELING OFF BACK AT FL310, CENTER ISSUED CLB INSTRUCTIONS TO FL330. NO MENTION OF OR QUERY WAS MADE BY THE CENTER CTLR OF OUR ALT DEVIATION. HUMAN PERFORMANCE CONSIDERATIONS. BOTH OF US FAILED TO RECOGNIZE THE FAST RATE AT WHICH THE CELLS WERE BUILDING AND GROWING TOGETHER. AN EARLIER DECISION TO ABANDON OUR INITIAL PLAN AND OPT TO GO AROUND THE LINE WOULD HAVE AVOIDED THE LAST MINUTE ABRUPT TURN REVERSAL. THE CAPT WAS VERY CONCERNED THAT WE NOT ENTER THE CELL, THUS THE SHARPNESS OF THE TURN USED TO AVOID THE AREA.

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.