Narrative:

Departing runway 31L at intersection kk at jfk with approximately 11000 ft of runway available. We planned on a reduced temperature takeoff using the noise sensitive climb profile on departure with flaps 20 degrees. Previously; our company allowed us to use a maximum derate of 20% from maximum power setting. Now with our onboard performance system we can further derate power up to 25% using runway specific data and inputting current WX conditions. At jfk conditions were: wind 240 degrees at 7 KTS; temperature 26 degrees C; and barometric pressure 30.03. Our old procedure allowing a 20% reduction provided a maximum allowable takeoff gross weight of 356300 KG; our actual weight was 346000 KG; thus we had a 10300 KG pad. By using the onboard performance system we further reduced our power setting 5% more to a derated temperature of 52 degrees C; providing a maximum allowable takeoff gross weight of 347946 KG at intersection kk; and an approximately pad of 1800 KG. The intent of this lower power takeoff is to significantly reduce engine wear. The takeoff itself seemed somewhat slower in accelerating such that we rotated the aircraft with 2000 ft of runway remaining; and the initial climb out was shallower such that we may have set off a noise monitor on the climb out. Conclusion: I will more closely evaluate when to use the maximum derate thrust setting. If it is a noise sensitive airport I would not opt for this low of a thrust setting; nor if there is an altitude constraint on the climb out.

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Original NASA ASRS Text

Title: B747 CAPTAIN IS CONCERNED THAT THE NEW ONBOARD PERFORMANCE COMPUTER POWER SETTING MAY NOT HAVE COMPLIED WITH JFK NOISE ABATEMENT PROCEDURES.

Narrative: DEPARTING RWY 31L AT INTXN KK AT JFK WITH APPROX 11000 FT OF RWY AVAILABLE. WE PLANNED ON A REDUCED TEMP TKOF USING THE NOISE SENSITIVE CLB PROFILE ON DEP WITH FLAPS 20 DEGS. PREVIOUSLY; OUR COMPANY ALLOWED US TO USE A MAX DERATE OF 20% FROM MAX PWR SETTING. NOW WITH OUR ONBOARD PERFORMANCE SYS WE CAN FURTHER DERATE PWR UP TO 25% USING RWY SPECIFIC DATA AND INPUTTING CURRENT WX CONDITIONS. AT JFK CONDITIONS WERE: WIND 240 DEGS AT 7 KTS; TEMP 26 DEGS C; AND BAROMETRIC PRESSURE 30.03. OUR OLD PROC ALLOWING A 20% REDUCTION PROVIDED A MAX ALLOWABLE TKOF GROSS WT OF 356300 KG; OUR ACTUAL WT WAS 346000 KG; THUS WE HAD A 10300 KG PAD. BY USING THE ONBOARD PERFORMANCE SYS WE FURTHER REDUCED OUR PWR SETTING 5% MORE TO A DERATED TEMP OF 52 DEGS C; PROVIDING A MAX ALLOWABLE TKOF GROSS WT OF 347946 KG AT INTXN KK; AND AN APPROX PAD OF 1800 KG. THE INTENT OF THIS LOWER PWR TKOF IS TO SIGNIFICANTLY REDUCE ENG WEAR. THE TKOF ITSELF SEEMED SOMEWHAT SLOWER IN ACCELERATING SUCH THAT WE ROTATED THE ACFT WITH 2000 FT OF RWY REMAINING; AND THE INITIAL CLBOUT WAS SHALLOWER SUCH THAT WE MAY HAVE SET OFF A NOISE MONITOR ON THE CLBOUT. CONCLUSION: I WILL MORE CLOSELY EVALUATE WHEN TO USE THE MAX DERATE THRUST SETTING. IF IT IS A NOISE SENSITIVE ARPT I WOULD NOT OPT FOR THIS LOW OF A THRUST SETTING; NOR IF THERE IS AN ALT CONSTRAINT ON THE CLBOUT.

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.