Narrative:

Last day of a 4 day trip. I was making the takeoff. Trip was an initial first officer upgrade line operating experience. Captain had delayed takeoff due to thunderstorms in the vicinity of lga and reports of moderate turbulence shortly after takeoff by departing aircraft. Thunderstorms moved away from the field and departing aircraft reported better conditions after takeoff (occasional light turbulence). We received a 4 min takeoff delay due to in trail restriction. At the time we were cleared for takeoff there was no precipitation, winds 260/4, no LLWS warnings. Aircraft weight was 167000 pounds, 8000 pounds below runway limit weight and maximum takeoff weight. We began our takeoff roll on runway 31, I was flying with the captain handling the throttles per our company policy. Engine runup and initial aircraft acceleration were normal. Captain called V1 then there was a longer than normal delay for the vr call (we did not attain vr and it was not called). Captain then called, 'I've got it,' and firewalled the throttled. I called, 'you got it,' and transitioned to the non flying role. I checked the airspeed which was below V1 and that all engines were running. The aircraft then remained V1 and lifted off slightly above vr in the last 500' of runway. After verifying a stable climb rate and airspeed we cleaned up the aircraft, reduced thrust below red line, and advised tower that we encountered windshear, overtemped the engines and were returning to the airport. We were handed off to departure, got vectors to ILS final while we dumped 7000 pounds of fuel. (We elected to land immediately since we did not know if any damage had been done to the engines when we overtemped them.) we completed the appropriate checklists and made an overweight landing (maximum landing weight 150M, our weight 157M). After landing we made a passenger announcement, had the emergency equipment check for hot brakes, and taxied to the gate. I felt we took ample precautions to avoid windshear and probably encountered a very localized, short-lived microburst (no other aircraft took off within 5 mins of us, no other aircraft reported any shear indications). Once the shear was encountered the captain felt there was inadequate stopping room (I agree) and elected to continue the takeoff. Maximum thrust was used and probably was what enabled us to get airborne prior to the end of the runway. The only way I feel this could have been avoided is with better low level wind shear detection equipment. Note: it also raises some interesting questions about non engine, performance related problems between V1 and vr. Note: captain said airspeed loss was 20-25 KTS.

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Original NASA ASRS Text

Title: ACR LGT ENCOUNTERED LOW LEVEL WIND SHEAR AT V1. ENGINE EGT OVERTEMPED TO ATTAIN AND MAINTAIN FLYING SPEED. DUMPED FUEL RETURN LAND.

Narrative: LAST DAY OF A 4 DAY TRIP. I WAS MAKING THE TKOF. TRIP WAS AN INITIAL F/O UPGRADE LINE OPERATING EXPERIENCE. CAPT HAD DELAYED TKOF DUE TO TSTMS IN THE VICINITY OF LGA AND RPTS OF MODERATE TURB SHORTLY AFTER TKOF BY DEPARTING ACFT. TSTMS MOVED AWAY FROM THE FIELD AND DEPARTING ACFT RPTED BETTER CONDITIONS AFTER TKOF (OCCASIONAL LIGHT TURB). WE RECEIVED A 4 MIN TKOF DELAY DUE TO IN TRAIL RESTRICTION. AT THE TIME WE WERE CLRED FOR TKOF THERE WAS NO PRECIP, WINDS 260/4, NO LLWS WARNINGS. ACFT WT WAS 167000 LBS, 8000 LBS BELOW RWY LIMIT WT AND MAX TKOF WT. WE BEGAN OUR TKOF ROLL ON RWY 31, I WAS FLYING WITH THE CAPT HANDLING THE THROTTLES PER OUR COMPANY POLICY. ENG RUNUP AND INITIAL ACFT ACCELERATION WERE NORMAL. CAPT CALLED V1 THEN THERE WAS A LONGER THAN NORMAL DELAY FOR THE VR CALL (WE DID NOT ATTAIN VR AND IT WAS NOT CALLED). CAPT THEN CALLED, 'I'VE GOT IT,' AND FIREWALLED THE THROTTLED. I CALLED, 'YOU GOT IT,' AND TRANSITIONED TO THE NON FLYING ROLE. I CHKED THE AIRSPD WHICH WAS BELOW V1 AND THAT ALL ENGS WERE RUNNING. THE ACFT THEN REMAINED V1 AND LIFTED OFF SLIGHTLY ABOVE VR IN THE LAST 500' OF RWY. AFTER VERIFYING A STABLE CLB RATE AND AIRSPD WE CLEANED UP THE ACFT, REDUCED THRUST BELOW RED LINE, AND ADVISED TWR THAT WE ENCOUNTERED WINDSHEAR, OVERTEMPED THE ENGS AND WERE RETURNING TO THE ARPT. WE WERE HANDED OFF TO DEP, GOT VECTORS TO ILS FINAL WHILE WE DUMPED 7000 LBS OF FUEL. (WE ELECTED TO LAND IMMEDIATELY SINCE WE DID NOT KNOW IF ANY DAMAGE HAD BEEN DONE TO THE ENGS WHEN WE OVERTEMPED THEM.) WE COMPLETED THE APPROPRIATE CHKLISTS AND MADE AN OVERWEIGHT LNDG (MAX LNDG WT 150M, OUR WT 157M). AFTER LNDG WE MADE A PAX ANNOUNCEMENT, HAD THE EMER EQUIP CHK FOR HOT BRAKES, AND TAXIED TO THE GATE. I FELT WE TOOK AMPLE PRECAUTIONS TO AVOID WINDSHEAR AND PROBABLY ENCOUNTERED A VERY LOCALIZED, SHORT-LIVED MICROBURST (NO OTHER ACFT TOOK OFF WITHIN 5 MINS OF US, NO OTHER ACFT RPTED ANY SHEAR INDICATIONS). ONCE THE SHEAR WAS ENCOUNTERED THE CAPT FELT THERE WAS INADEQUATE STOPPING ROOM (I AGREE) AND ELECTED TO CONTINUE THE TKOF. MAX THRUST WAS USED AND PROBABLY WAS WHAT ENABLED US TO GET AIRBORNE PRIOR TO THE END OF THE RWY. THE ONLY WAY I FEEL THIS COULD HAVE BEEN AVOIDED IS WITH BETTER LOW LEVEL WIND SHEAR DETECTION EQUIP. NOTE: IT ALSO RAISES SOME INTERESTING QUESTIONS ABOUT NON ENGINE, PERFORMANCE RELATED PROBS BTWN V1 AND VR. NOTE: CAPT SAID AIRSPD LOSS WAS 20-25 KTS.

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.