Narrative:

Preparing to taxi out; the WX was reported mild: wind 260 degrees at 19 KTS; 10 KM; 2000 ft broken; qnh 999 MB; temperature 7 degrees; dewpoint 0 degrees. An alternate noise abatement departure was required and briefed with a derated-2 thrust and relatively light weight of 116.9 pounds. The SID as cleared was briefed; an automatic switch to departure control; along with autoplt engagement pratt-engine based engagement procedures and the altimetry change for a transition altitude of 8000 ft. However; during taxi to takeoff; the ship's on board radar showed significant returns in the vicinity of the airport and the departure corridor. Upon turing onto the runway; as we were cleared for takeoff; the ship's radar showed what appeared to be 2 significant precipitation waves or possibly squall lines ahead on the departure track. The crew also noticed a sudden rise in surface wind speed at their location on the runway; and that the new wind was not along the runway heading. Within the wind gusts there was occurring significant precipitation. The crew informed the tower that the flight would not take off at this time due to the passing squall lines; would delay until the squall lines had passed; and would be willing to vacate the runway if needed. Tower acknowledged the flight's report; cancelled takeoff clearance and said that the flight should remain in position on this runway; since landing flts are arriving on another runway. That runway is lined up with the wind more closely than this runway (which was being used only for departures) and several arriving flts continued to a landing. However; no PIREPS of extreme turbulence were made on tower frequency by these arriving flts nor were any passed to our flight by ATC. The squall like WX continued and appeared on ship's radar to be moving rapidly from nnw across the departure corridor and the winds remained high. The flight held in position for a considerable time; between approximately 15-20 mins. During this time the ship's radar showed the squall lines to have moved off to the south and west of the departure corridor. Precipitation had decreased considerably and wind gusts appeared to have decreased markedly according to our own outside observations. The crew decided to set maximum rated thrust; however; to have the advantage of thrust available and decrease takeoff roll. The departure corridor now appeared safe for departure and the crew; based upon all available data and experience; accepted takeoff clearance. Takeoff roll; liftoff and initial climb were normal; and light rain and steady winds were encountered. However; with a light aircraft weight and maximum thrust; a relatively high nose attitude was directed by the flight director. Then unexpectedly; above 1000 ft extreme turbulence was experienced. As the flight approached 1500 ft AGL for the transition from takeoff to VNAV modes; the nose attitude was a little high and the pilot monitoring recommended that the PF decrease the nose attitude from about 29 degrees; back down towards 20 degrees. Nonetheless; even as the PF did lower the nose slightly; and VNAV mode was selected; the flight encountered extreme turbulence and a very brief momentary transitory stall warning indication event occurred. At this point the pilot monitoring decided that the most prudent thing to do was to take temporary control of the aircraft; lower the pitch attitude to about 22 degrees and push the power control levers to the full power position. During this time period the flight continued in extreme turbulence; and the pilot monitoring -- now PF -- held full power and about 22 degrees of pitch and continued a steady climb and transition to an area above and out of and past this area. As the area of extreme turbulence was exited; the crew resumed normal departure confign and navigation procedures and the pilot monitoring -- now PF -- returned control of the flight to the other flight crew member. The flight proceeded to destination without any further remarkable events. During the cruise portion of the flight; the crew held a discussion on windshear-like; extreme turbulence encounter procedures. If any lesson can be gained by this event from this relatively prudent captain's viewpoint; it is to exhibit even greater caution and rely on the ship's radar system less to determine possible areas of turbulence ahead on the flight path. Even though the flight crew delayeddep until it appeared on ship's radar that the squall areas had transited past the departure corridor; at night there is just not enough visual reference to see very far ahead into the sky; evidently; to make a prudent determination. Also; the ship's radar equipment; while excellent at displaying precipitation; is apparently not as excellent at displaying areas of extreme turbulence. In retrospect; it might have been more prudent to consider a further delay or even a block turn-back; in this circumstance; and even more so had it been known or expected that extreme turbulence was occurring at and above 1000 ft. Also; I would comment that the windshear recovery procedures which are taught in our training; such as in the windshear demonstration on takeoff; are very useful even when a short and accelerated stall is encountered due to extreme turbulence; even if that event occurred at an altitude above 1000 ft.

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Original NASA ASRS Text

Title: A B757 ENCOUNTERED SEVERE TURBULENCE ON DEP WITH A STALL WARNING DUE TO THE HIGH PITCH ATTITUDE OF THE LIGHT ACFT DURING THE TURBULENCE ONSET.

Narrative: PREPARING TO TAXI OUT; THE WX WAS RPTED MILD: WIND 260 DEGS AT 19 KTS; 10 KM; 2000 FT BROKEN; QNH 999 MB; TEMP 7 DEGS; DEWPOINT 0 DEGS. AN ALTERNATE NOISE ABATEMENT DEP WAS REQUIRED AND BRIEFED WITH A DERATED-2 THRUST AND RELATIVELY LIGHT WT OF 116.9 LBS. THE SID AS CLRED WAS BRIEFED; AN AUTOMATIC SWITCH TO DEP CTL; ALONG WITH AUTOPLT ENGAGEMENT PRATT-ENG BASED ENGAGEMENT PROCS AND THE ALTIMETRY CHANGE FOR A TRANSITION ALT OF 8000 FT. HOWEVER; DURING TAXI TO TKOF; THE SHIP'S ON BOARD RADAR SHOWED SIGNIFICANT RETURNS IN THE VICINITY OF THE ARPT AND THE DEP CORRIDOR. UPON TURING ONTO THE RWY; AS WE WERE CLRED FOR TKOF; THE SHIP'S RADAR SHOWED WHAT APPEARED TO BE 2 SIGNIFICANT PRECIP WAVES OR POSSIBLY SQUALL LINES AHEAD ON THE DEP TRACK. THE CREW ALSO NOTICED A SUDDEN RISE IN SURFACE WIND SPD AT THEIR LOCATION ON THE RWY; AND THAT THE NEW WIND WAS NOT ALONG THE RWY HDG. WITHIN THE WIND GUSTS THERE WAS OCCURRING SIGNIFICANT PRECIP. THE CREW INFORMED THE TWR THAT THE FLT WOULD NOT TAKE OFF AT THIS TIME DUE TO THE PASSING SQUALL LINES; WOULD DELAY UNTIL THE SQUALL LINES HAD PASSED; AND WOULD BE WILLING TO VACATE THE RWY IF NEEDED. TWR ACKNOWLEDGED THE FLT'S RPT; CANCELLED TKOF CLRNC AND SAID THAT THE FLT SHOULD REMAIN IN POS ON THIS RWY; SINCE LNDG FLTS ARE ARRIVING ON ANOTHER RWY. THAT RWY IS LINED UP WITH THE WIND MORE CLOSELY THAN THIS RWY (WHICH WAS BEING USED ONLY FOR DEPS) AND SEVERAL ARRIVING FLTS CONTINUED TO A LNDG. HOWEVER; NO PIREPS OF EXTREME TURB WERE MADE ON TWR FREQ BY THESE ARRIVING FLTS NOR WERE ANY PASSED TO OUR FLT BY ATC. THE SQUALL LIKE WX CONTINUED AND APPEARED ON SHIP'S RADAR TO BE MOVING RAPIDLY FROM NNW ACROSS THE DEP CORRIDOR AND THE WINDS REMAINED HIGH. THE FLT HELD IN POS FOR A CONSIDERABLE TIME; BTWN APPROX 15-20 MINS. DURING THIS TIME THE SHIP'S RADAR SHOWED THE SQUALL LINES TO HAVE MOVED OFF TO THE S AND W OF THE DEP CORRIDOR. PRECIP HAD DECREASED CONSIDERABLY AND WIND GUSTS APPEARED TO HAVE DECREASED MARKEDLY ACCORDING TO OUR OWN OUTSIDE OBSERVATIONS. THE CREW DECIDED TO SET MAX RATED THRUST; HOWEVER; TO HAVE THE ADVANTAGE OF THRUST AVAILABLE AND DECREASE TKOF ROLL. THE DEP CORRIDOR NOW APPEARED SAFE FOR DEP AND THE CREW; BASED UPON ALL AVAILABLE DATA AND EXPERIENCE; ACCEPTED TKOF CLRNC. TKOF ROLL; LIFTOFF AND INITIAL CLB WERE NORMAL; AND LIGHT RAIN AND STEADY WINDS WERE ENCOUNTERED. HOWEVER; WITH A LIGHT ACFT WT AND MAX THRUST; A RELATIVELY HIGH NOSE ATTITUDE WAS DIRECTED BY THE FLT DIRECTOR. THEN UNEXPECTEDLY; ABOVE 1000 FT EXTREME TURB WAS EXPERIENCED. AS THE FLT APCHED 1500 FT AGL FOR THE TRANSITION FROM TKOF TO VNAV MODES; THE NOSE ATTITUDE WAS A LITTLE HIGH AND THE PLT MONITORING RECOMMENDED THAT THE PF DECREASE THE NOSE ATTITUDE FROM ABOUT 29 DEGS; BACK DOWN TOWARDS 20 DEGS. NONETHELESS; EVEN AS THE PF DID LOWER THE NOSE SLIGHTLY; AND VNAV MODE WAS SELECTED; THE FLT ENCOUNTERED EXTREME TURB AND A VERY BRIEF MOMENTARY TRANSITORY STALL WARNING INDICATION EVENT OCCURRED. AT THIS POINT THE PLT MONITORING DECIDED THAT THE MOST PRUDENT THING TO DO WAS TO TAKE TEMPORARY CTL OF THE ACFT; LOWER THE PITCH ATTITUDE TO ABOUT 22 DEGS AND PUSH THE PWR CTL LEVERS TO THE FULL PWR POS. DURING THIS TIME PERIOD THE FLT CONTINUED IN EXTREME TURB; AND THE PLT MONITORING -- NOW PF -- HELD FULL PWR AND ABOUT 22 DEGS OF PITCH AND CONTINUED A STEADY CLB AND TRANSITION TO AN AREA ABOVE AND OUT OF AND PAST THIS AREA. AS THE AREA OF EXTREME TURB WAS EXITED; THE CREW RESUMED NORMAL DEP CONFIGN AND NAV PROCS AND THE PLT MONITORING -- NOW PF -- RETURNED CTL OF THE FLT TO THE OTHER FLT CREW MEMBER. THE FLT PROCEEDED TO DEST WITHOUT ANY FURTHER REMARKABLE EVENTS. DURING THE CRUISE PORTION OF THE FLT; THE CREW HELD A DISCUSSION ON WINDSHEAR-LIKE; EXTREME TURB ENCOUNTER PROCS. IF ANY LESSON CAN BE GAINED BY THIS EVENT FROM THIS RELATIVELY PRUDENT CAPT'S VIEWPOINT; IT IS TO EXHIBIT EVEN GREATER CAUTION AND RELY ON THE SHIP'S RADAR SYS LESS TO DETERMINE POSSIBLE AREAS OF TURB AHEAD ON THE FLT PATH. EVEN THOUGH THE FLT CREW DELAYEDDEP UNTIL IT APPEARED ON SHIP'S RADAR THAT THE SQUALL AREAS HAD TRANSITED PAST THE DEP CORRIDOR; AT NIGHT THERE IS JUST NOT ENOUGH VISUAL REF TO SEE VERY FAR AHEAD INTO THE SKY; EVIDENTLY; TO MAKE A PRUDENT DETERMINATION. ALSO; THE SHIP'S RADAR EQUIP; WHILE EXCELLENT AT DISPLAYING PRECIP; IS APPARENTLY NOT AS EXCELLENT AT DISPLAYING AREAS OF EXTREME TURB. IN RETROSPECT; IT MIGHT HAVE BEEN MORE PRUDENT TO CONSIDER A FURTHER DELAY OR EVEN A BLOCK TURN-BACK; IN THIS CIRCUMSTANCE; AND EVEN MORE SO HAD IT BEEN KNOWN OR EXPECTED THAT EXTREME TURB WAS OCCURRING AT AND ABOVE 1000 FT. ALSO; I WOULD COMMENT THAT THE WINDSHEAR RECOVERY PROCS WHICH ARE TAUGHT IN OUR TRAINING; SUCH AS IN THE WINDSHEAR DEMO ON TKOF; ARE VERY USEFUL EVEN WHEN A SHORT AND ACCELERATED STALL IS ENCOUNTERED DUE TO EXTREME TURB; EVEN IF THAT EVENT OCCURRED AT AN ALT ABOVE 1000 FT.

Data retrieved from NASA's ASRS site as of January 2009 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.