Narrative:

I was in a late model medium large transport on a flight from dal to abq. On taxi-out, the first officer figured the assumed temperature for a reduced thrust takeoff and typed it into the computer. I had noticed that the N1 that the CDU had presented (about 83.5%) seemed to be a little low for a relatively heavy aircraft (about 117000#) and I asked him to check the assumed temperature. He did this and pronounced it to be correct. I assumed it was me that just could not get used to what a remarkable performer the aircraft was. Cleared for takeoff, we set the prescribed N1 and started to roll. Normally, we have to hurry to get the power set before we pass 80 KIAS. This time, we set it and still had to wait for the speed call. 1/2-way down the runway, I was becoming more aware of our lack of acceleration. I pushed the thrust levers up to about 90%. We accelerated and rotated in the last 1000' of the runway and climbed out at about 1500 FPM, well below the high rates we are accustomed to. When we reached our cruise level, I got the load sheet and the performance manual out and went over what we had. I discovered that the first officer had become confused over the columns of temperatures (see the enclosed sample airport analysis) and had entered the temperature under 'maximum assume temperature degree F.' instead of entering 98 degrees F, he had entered 146 degrees. With the lightest of loads, our maximum reduction should have been limited to 141 degrees F. Outside air temperature was 74 degrees F. The computer had accepted it and we had, in effect, self-induced an unsafe takeoff with less than climb power set on a very heavy aircraft. I set the correct data in the CDU, and it showed we should have set an N1 of 91.5%. This was 8% above what we set for takeoff and above what I set midway down the runway. How did this happen and why didn't I instinctively know it was wrong? Nobody checks the first officer. He is just supposed to do it right. On the -200 the captain has the totalizer to double-check the speeds. He knows that the maximum reduction is .12 EPR. This equates to about 12000 pounds from the maximum ATOG. We have a given ballpark of parameters which double-checks a first officer who makes a glaring error. We know what a significant reduction is and we know if it is plausible. This can't happen on a 200! The CDU will accept anything in figuring reduced takeoff N1. It will not accept certain data if incorrect and perhaps it could be programmed to consider more input when accepting an assumed temperature. Some parameters that could be considered are: the difference between the outside air temperature and the assumed temperature, the difference between the maximum 0 fuel weight and the actual 0 fuel weight. It should not accept such a glaring error. The CDU will often give takeoff N1's well below climb thrust. Is this prudent? Could we not use climb thrust as the maximum amount of reduction allowed? It would serve as 1 more check on the system. Poor procedures. I was shocked to learn that other capts have experienced this error in some form or other. Many have adjusted their techniques to prevent another. Some will not accept a reduced thrust takeoff if the actual aircraft weight is over 110000#. Others will limit the maximum assumed temperature to 120 degrees F. Either technique would have prevented me from having the low power setting. We need to recognize and realize that any person could make this error. We need to back him up, either with the help of a more selective CDU or with different techniques and procedures. I hope this report helps to do that.

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Original NASA ASRS Text

Title: ACR MLG STARTED TKOF ROLL WITH POWER SET TOO LOW FOR ACFT GROSS WEIGHT. FLT CREW HAD USED WRONG ASSUMED TEMPERATURE WHEN USING THE CDU TO COMPUTE MAXIMUM REDUCED THRUST.

Narrative: I WAS IN A LATE MODEL MLG ON A FLT FROM DAL TO ABQ. ON TAXI-OUT, THE F/O FIGURED THE ASSUMED TEMP FOR A REDUCED THRUST TKOF AND TYPED IT INTO THE COMPUTER. I HAD NOTICED THAT THE N1 THAT THE CDU HAD PRESENTED (ABOUT 83.5%) SEEMED TO BE A LITTLE LOW FOR A RELATIVELY HEAVY ACFT (ABOUT 117000#) AND I ASKED HIM TO CHK THE ASSUMED TEMP. HE DID THIS AND PRONOUNCED IT TO BE CORRECT. I ASSUMED IT WAS ME THAT JUST COULD NOT GET USED TO WHAT A REMARKABLE PERFORMER THE ACFT WAS. CLRED FOR TKOF, WE SET THE PRESCRIBED N1 AND STARTED TO ROLL. NORMALLY, WE HAVE TO HURRY TO GET THE PWR SET BEFORE WE PASS 80 KIAS. THIS TIME, WE SET IT AND STILL HAD TO WAIT FOR THE SPD CALL. 1/2-WAY DOWN THE RWY, I WAS BECOMING MORE AWARE OF OUR LACK OF ACCELERATION. I PUSHED THE THRUST LEVERS UP TO ABOUT 90%. WE ACCELERATED AND ROTATED IN THE LAST 1000' OF THE RWY AND CLBED OUT AT ABOUT 1500 FPM, WELL BELOW THE HIGH RATES WE ARE ACCUSTOMED TO. WHEN WE REACHED OUR CRUISE LEVEL, I GOT THE LOAD SHEET AND THE PERFORMANCE MANUAL OUT AND WENT OVER WHAT WE HAD. I DISCOVERED THAT THE F/O HAD BECOME CONFUSED OVER THE COLUMNS OF TEMPS (SEE THE ENCLOSED SAMPLE ARPT ANALYSIS) AND HAD ENTERED THE TEMP UNDER 'MAX ASSUME TEMP DEG F.' INSTEAD OF ENTERING 98 DEGS F, HE HAD ENTERED 146 DEGS. WITH THE LIGHTEST OF LOADS, OUR MAX REDUCTION SHOULD HAVE BEEN LIMITED TO 141 DEGS F. OUTSIDE AIR TEMP WAS 74 DEGS F. THE COMPUTER HAD ACCEPTED IT AND WE HAD, IN EFFECT, SELF-INDUCED AN UNSAFE TKOF WITH LESS THAN CLB PWR SET ON A VERY HEAVY ACFT. I SET THE CORRECT DATA IN THE CDU, AND IT SHOWED WE SHOULD HAVE SET AN N1 OF 91.5%. THIS WAS 8% ABOVE WHAT WE SET FOR TKOF AND ABOVE WHAT I SET MIDWAY DOWN THE RWY. HOW DID THIS HAPPEN AND WHY DIDN'T I INSTINCTIVELY KNOW IT WAS WRONG? NOBODY CHKS THE F/O. HE IS JUST SUPPOSED TO DO IT RIGHT. ON THE -200 THE CAPT HAS THE TOTALIZER TO DOUBLE-CHK THE SPDS. HE KNOWS THAT THE MAX REDUCTION IS .12 EPR. THIS EQUATES TO ABOUT 12000 LBS FROM THE MAX ATOG. WE HAVE A GIVEN BALLPARK OF PARAMETERS WHICH DOUBLE-CHKS A F/O WHO MAKES A GLARING ERROR. WE KNOW WHAT A SIGNIFICANT REDUCTION IS AND WE KNOW IF IT IS PLAUSIBLE. THIS CAN'T HAPPEN ON A 200! THE CDU WILL ACCEPT ANYTHING IN FIGURING REDUCED TKOF N1. IT WILL NOT ACCEPT CERTAIN DATA IF INCORRECT AND PERHAPS IT COULD BE PROGRAMMED TO CONSIDER MORE INPUT WHEN ACCEPTING AN ASSUMED TEMP. SOME PARAMETERS THAT COULD BE CONSIDERED ARE: THE DIFFERENCE BTWN THE OUTSIDE AIR TEMP AND THE ASSUMED TEMP, THE DIFFERENCE BTWN THE MAX 0 FUEL WT AND THE ACTUAL 0 FUEL WT. IT SHOULD NOT ACCEPT SUCH A GLARING ERROR. THE CDU WILL OFTEN GIVE TKOF N1'S WELL BELOW CLB THRUST. IS THIS PRUDENT? COULD WE NOT USE CLB THRUST AS THE MAX AMOUNT OF REDUCTION ALLOWED? IT WOULD SERVE AS 1 MORE CHK ON THE SYS. POOR PROCS. I WAS SHOCKED TO LEARN THAT OTHER CAPTS HAVE EXPERIENCED THIS ERROR IN SOME FORM OR OTHER. MANY HAVE ADJUSTED THEIR TECHNIQUES TO PREVENT ANOTHER. SOME WILL NOT ACCEPT A REDUCED THRUST TKOF IF THE ACTUAL ACFT WEIGHT IS OVER 110000#. OTHERS WILL LIMIT THE MAX ASSUMED TEMP TO 120 DEGS F. EITHER TECHNIQUE WOULD HAVE PREVENTED ME FROM HAVING THE LOW PWR SETTING. WE NEED TO RECOGNIZE AND REALIZE THAT ANY PERSON COULD MAKE THIS ERROR. WE NEED TO BACK HIM UP, EITHER WITH THE HELP OF A MORE SELECTIVE CDU OR WITH DIFFERENT TECHNIQUES AND PROCS. I HOPE THIS RPT HELPS TO DO THAT.

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.