Narrative:

We pushed back at oak. Shortly after pushback the ground crew advised the captain that we were cleared to start. While the captain accomplished the start, I copied the weight and balance numbers from operations. I noticed that the takeoff weight seemed low. It was 20000 pounds below our maximum release weight. However, when I added the zero fuel weight and fuel together it was the same takeoff weight that I had been given. I consulted the quick reference performance manual and determined that we could use 20 KTS reduced power with the maximum allowable reduction for assumed temperature. I entered the takeoff speeds into the FMC and I completed the takeoff briefing. We then completed the taxi and takeoff check. It was my leg and I began what seemed at first to be a normal takeoff. As we accelerated through V1 and vr, everything was normal. As I began to rotate, the nose felt heavy. As the rotation continued through 9 degrees, I began to have to push instead of pull to slow down the rotation. As the aircraft lifted off, we felt and heard a thud. The tail had struck the ground. We continued the takeoff and climb out but returned immediately to oak. The approach and landing were normal. Upon our return examination of the aircraft showed 2 antennas on the aft belly broken off and 3 scraped areas on the aft belly skin ahead of the tailskid. All of the damage turned out to be superficial. After checking the aircraft I went to operations where I learned that the takeoff weights we had been given were 18000 pounds less than the actual takeoff weight. Operations had made a mistake in the weight and balance computations. In retrospect, I believe the following to be contributing factors: 1) we use manual computations for our weight and balance. This leads to possible mistakes such as this incident. 2) we currently have no procedure for the flight crew to xchk the zero fuel weight against our load -- we merely add the zero fuel weight we are given to the fuel as a xchk. 3) from pushback to takeoff was only 6 mins. Perhaps if we had taken more time we might have noticed the large difference between our release weight and actual takeoff weight and investigated further.

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Original NASA ASRS Text

Title: B737-400 ACFT FLC NOTICED PRIOR TO TAXI THAT FINAL TKOF WT WAS LOW, BUT WHEN RPTR FO ADDED THE FUEL TO THE ZERO FUEL WT, IT CAME OUT THE SAME. NEW WT AND SPDS WERE ENTERED INTO THE FMC. ON ROTATION IN TKOF ROLL, RPTR FO PF NOTED THE NOSE SEEMED HVY, THEN HAD TO PUSH BECAUSE OF THE RAPID ROTATION. TAIL STRIKE OCCURRED AND FLC RETURN LAND, AND FOUND DAMAGE TO UNDERSIDE OF ACFT.

Narrative: WE PUSHED BACK AT OAK. SHORTLY AFTER PUSHBACK THE GND CREW ADVISED THE CAPT THAT WE WERE CLRED TO START. WHILE THE CAPT ACCOMPLISHED THE START, I COPIED THE WT AND BAL NUMBERS FROM OPS. I NOTICED THAT THE TKOF WT SEEMED LOW. IT WAS 20000 LBS BELOW OUR MAX RELEASE WT. HOWEVER, WHEN I ADDED THE ZERO FUEL WT AND FUEL TOGETHER IT WAS THE SAME TKOF WT THAT I HAD BEEN GIVEN. I CONSULTED THE QUICK REF PERFORMANCE MANUAL AND DETERMINED THAT WE COULD USE 20 KTS REDUCED PWR WITH THE MAX ALLOWABLE REDUCTION FOR ASSUMED TEMP. I ENTERED THE TKOF SPDS INTO THE FMC AND I COMPLETED THE TKOF BRIEFING. WE THEN COMPLETED THE TAXI AND TKOF CHK. IT WAS MY LEG AND I BEGAN WHAT SEEMED AT FIRST TO BE A NORMAL TKOF. AS WE ACCELERATED THROUGH V1 AND VR, EVERYTHING WAS NORMAL. AS I BEGAN TO ROTATE, THE NOSE FELT HVY. AS THE ROTATION CONTINUED THROUGH 9 DEGS, I BEGAN TO HAVE TO PUSH INSTEAD OF PULL TO SLOW DOWN THE ROTATION. AS THE ACFT LIFTED OFF, WE FELT AND HEARD A THUD. THE TAIL HAD STRUCK THE GND. WE CONTINUED THE TKOF AND CLBOUT BUT RETURNED IMMEDIATELY TO OAK. THE APCH AND LNDG WERE NORMAL. UPON OUR RETURN EXAM OF THE ACFT SHOWED 2 ANTENNAS ON THE AFT BELLY BROKEN OFF AND 3 SCRAPED AREAS ON THE AFT BELLY SKIN AHEAD OF THE TAILSKID. ALL OF THE DAMAGE TURNED OUT TO BE SUPERFICIAL. AFTER CHKING THE ACFT I WENT TO OPS WHERE I LEARNED THAT THE TKOF WTS WE HAD BEEN GIVEN WERE 18000 LBS LESS THAN THE ACTUAL TKOF WT. OPS HAD MADE A MISTAKE IN THE WT AND BAL COMPUTATIONS. IN RETROSPECT, I BELIEVE THE FOLLOWING TO BE CONTRIBUTING FACTORS: 1) WE USE MANUAL COMPUTATIONS FOR OUR WT AND BAL. THIS LEADS TO POSSIBLE MISTAKES SUCH AS THIS INCIDENT. 2) WE CURRENTLY HAVE NO PROC FOR THE FLC TO XCHK THE ZERO FUEL WT AGAINST OUR LOAD -- WE MERELY ADD THE ZERO FUEL WT WE ARE GIVEN TO THE FUEL AS A XCHK. 3) FROM PUSHBACK TO TKOF WAS ONLY 6 MINS. PERHAPS IF WE HAD TAKEN MORE TIME WE MIGHT HAVE NOTICED THE LARGE DIFFERENCE BTWN OUR RELEASE WT AND ACTUAL TKOF WT AND INVESTIGATED FURTHER.

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.