Narrative:

Flight delayed 2 hours for cargo xfer between osaka bound and narita bound aircraft. Original scheduled departure XA20 new planned departure XC20. Planned takeoff gross weight 500477 pounds. Planned fuel on board: 155500 pounds. Used anti-ice takeoff data due to slush on txwys and runway. Runway 22 data: maximum N1 - - 110.5. ATOG 585500 -- runway limit. ATOG 596300 -- performance limit. Fuel on board, prior to pushback -- 157400. XC28Z -- pushed back. XC35Z -- requested final weights via ACARS, received planned weight manifest via ACARS. XC38Z -- called station via voice regarding final weights, station said stand by. XC39Z -- received final weights via ACARS, negligible weight and trim changes. XC42Z -- liftoff, normal. XC43Z -- secured engine anti-ice. Climb out normal, clear, smooth. Approximately XC50Z received clearance to FL390, checked books and advised ATC FL390 was not acceptable, but FL350 was acceptable cruise level. (Considerations for aircraft weight and temperature were taken into account.) received clearance to FL350. Normal SOP climb, smooth, clear. Approaching FL340, aircraft climb performance slowly began to deteriorate. Reduced rate of climb to maintain normal climb airspeed. Approximately 300-500 FPM climb. Mach slowed to .78, assured maximum N1 for climb on all engines. Continued to reduce rate of climb to approximately 100 FPM approaching FL347. After altitude capture and altitude hold, FL350 with maximum N1 climb mode selected and verified on each engine, speed began to deteriorate rapidly. Airframe buffet developed. Mach .722, sat -52, tat -26 was noted. Gross weight 486000 pounds. Requested lower immediately. Unable lower due to traffic, controller gave off route vector. Told so to shut off second pack and pneumatic supply. He secured pack and pneumatic supply, and streamlined inlet door for minimum drag. Aircraft buffet continued to increase. Initiated slow descent (100- 200 FPM) while awaiting ATC clearance. TCASII showed aircraft at approximately 7-8 O'clock, 5 NM, 2000 ft below. Other aircraft advised visual contact with us. We advised visual contact and leveled at FL347 awaiting lower. Aircraft continued to buffet, initiated slow descent and simultaneously received clearance to FL310. Increased rate of descent and buffet dissipated. Aircraft confign was normal for phase of flight. Stick shaker did not activate and automatic slats did not extend. Leveled at FL310, established normal cruise. Upon review of data, noticed approximately a 16 degree isa temperature change (increase) between FL310 and FL350. At FL310, sat -56. At FL350, sat -52. Cruise charts showed maximum cruise weight 495000 pounds at isa plus 10 and 498500 pounds at isa plus 20. Actual weight was 486000 and isa plus 2. Investigated all possible reasons for problem. Determined that the most probable cause for inadequate performance must be cargo weight miscalculation. Notified dispatch of possible problem and estimated weight of aircraft to be at least 20000 pounds heavier than paperwork indicated. AC15Z -- received message from dispatch via commercial radio that preliminary indications show aircraft to be at least 20000 pounds more than flight plan form. New plan instructed us to delay climb to FL350 until reaching nates intersection. Remained at FL310 due to traffic restrs. Remainder of flight was normal. Supplemental information from acn 395500: takeoff weight 500000 pounds. Upon reaching FL350 gross weight was 486000 pounds. Flight manual maximum weight for FL350 shows 495000 with 300 ft rate of climb. Upon reaching FL350 and in level flight the aircraft continued to decelerate and began to buffet. I strongly believe we weighed at least 520000 pounds on takeoff and the reason that we encountered stall buffet was that upon reaching FL350 we weighed at least 506000 pounds. We asked dispatch to weigh cargo upon arrival in narita. Also notified dispatch of suspected weight error.

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Original NASA ASRS Text

Title: A DC10 IS CLRED TO A HIGHER ALT BY ZAN BUT IS UNABLE TO MAINTAIN THAT ALT AS THE ACFT IS HEAVIER THAN FORECAST FOR THAT FLT PLAN POS. ACFT REACHES A BUFFET AND DSNDS 4000 FT WHERE ACFT HAS ENOUGH PWR FOR THE WT OF THE ACFT TO CRUISE AND MAINTAIN ALT.

Narrative: FLT DELAYED 2 HRS FOR CARGO XFER BTWN OSAKA BOUND AND NARITA BOUND ACFT. ORIGINAL SCHEDULED DEP XA20 NEW PLANNED DEP XC20. PLANNED TKOF GROSS WT 500477 LBS. PLANNED FUEL ON BOARD: 155500 LBS. USED ANTI-ICE TKOF DATA DUE TO SLUSH ON TXWYS AND RWY. RWY 22 DATA: MAX N1 - - 110.5. ATOG 585500 -- RWY LIMIT. ATOG 596300 -- PERFORMANCE LIMIT. FUEL ON BOARD, PRIOR TO PUSHBACK -- 157400. XC28Z -- PUSHED BACK. XC35Z -- REQUESTED FINAL WTS VIA ACARS, RECEIVED PLANNED WT MANIFEST VIA ACARS. XC38Z -- CALLED STATION VIA VOICE REGARDING FINAL WTS, STATION SAID STAND BY. XC39Z -- RECEIVED FINAL WTS VIA ACARS, NEGLIGIBLE WT AND TRIM CHANGES. XC42Z -- LIFTOFF, NORMAL. XC43Z -- SECURED ENG ANTI-ICE. CLBOUT NORMAL, CLR, SMOOTH. APPROX XC50Z RECEIVED CLRNC TO FL390, CHKED BOOKS AND ADVISED ATC FL390 WAS NOT ACCEPTABLE, BUT FL350 WAS ACCEPTABLE CRUISE LEVEL. (CONSIDERATIONS FOR ACFT WT AND TEMP WERE TAKEN INTO ACCOUNT.) RECEIVED CLRNC TO FL350. NORMAL SOP CLB, SMOOTH, CLR. APCHING FL340, ACFT CLB PERFORMANCE SLOWLY BEGAN TO DETERIORATE. REDUCED RATE OF CLB TO MAINTAIN NORMAL CLB AIRSPD. APPROX 300-500 FPM CLB. MACH SLOWED TO .78, ASSURED MAX N1 FOR CLB ON ALL ENGS. CONTINUED TO REDUCE RATE OF CLB TO APPROX 100 FPM APCHING FL347. AFTER ALT CAPTURE AND ALT HOLD, FL350 WITH MAX N1 CLB MODE SELECTED AND VERIFIED ON EACH ENG, SPD BEGAN TO DETERIORATE RAPIDLY. AIRFRAME BUFFET DEVELOPED. MACH .722, SAT -52, TAT -26 WAS NOTED. GROSS WT 486000 LBS. REQUESTED LOWER IMMEDIATELY. UNABLE LOWER DUE TO TFC, CTLR GAVE OFF RTE VECTOR. TOLD SO TO SHUT OFF SECOND PACK AND PNEUMATIC SUPPLY. HE SECURED PACK AND PNEUMATIC SUPPLY, AND STREAMLINED INLET DOOR FOR MINIMUM DRAG. ACFT BUFFET CONTINUED TO INCREASE. INITIATED SLOW DSCNT (100- 200 FPM) WHILE AWAITING ATC CLRNC. TCASII SHOWED ACFT AT APPROX 7-8 O'CLOCK, 5 NM, 2000 FT BELOW. OTHER ACFT ADVISED VISUAL CONTACT WITH US. WE ADVISED VISUAL CONTACT AND LEVELED AT FL347 AWAITING LOWER. ACFT CONTINUED TO BUFFET, INITIATED SLOW DSCNT AND SIMULTANEOUSLY RECEIVED CLRNC TO FL310. INCREASED RATE OF DSCNT AND BUFFET DISSIPATED. ACFT CONFIGN WAS NORMAL FOR PHASE OF FLT. STICK SHAKER DID NOT ACTIVATE AND AUTO SLATS DID NOT EXTEND. LEVELED AT FL310, ESTABLISHED NORMAL CRUISE. UPON REVIEW OF DATA, NOTICED APPROX A 16 DEG ISA TEMP CHANGE (INCREASE) BTWN FL310 AND FL350. AT FL310, SAT -56. AT FL350, SAT -52. CRUISE CHARTS SHOWED MAX CRUISE WT 495000 LBS AT ISA PLUS 10 AND 498500 LBS AT ISA PLUS 20. ACTUAL WT WAS 486000 AND ISA PLUS 2. INVESTIGATED ALL POSSIBLE REASONS FOR PROB. DETERMINED THAT THE MOST PROBABLE CAUSE FOR INADEQUATE PERFORMANCE MUST BE CARGO WT MISCALCULATION. NOTIFIED DISPATCH OF POSSIBLE PROB AND ESTIMATED WT OF ACFT TO BE AT LEAST 20000 LBS HEAVIER THAN PAPERWORK INDICATED. AC15Z -- RECEIVED MESSAGE FROM DISPATCH VIA COMMERCIAL RADIO THAT PRELIMINARY INDICATIONS SHOW ACFT TO BE AT LEAST 20000 LBS MORE THAN FLT PLAN FORM. NEW PLAN INSTRUCTED US TO DELAY CLB TO FL350 UNTIL REACHING NATES INTXN. REMAINED AT FL310 DUE TO TFC RESTRS. REMAINDER OF FLT WAS NORMAL. SUPPLEMENTAL INFO FROM ACN 395500: TKOF WT 500000 LBS. UPON REACHING FL350 GROSS WT WAS 486000 LBS. FLT MANUAL MAX WT FOR FL350 SHOWS 495000 WITH 300 FT RATE OF CLB. UPON REACHING FL350 AND IN LEVEL FLT THE ACFT CONTINUED TO DECELERATE AND BEGAN TO BUFFET. I STRONGLY BELIEVE WE WEIGHED AT LEAST 520000 LBS ON TKOF AND THE REASON THAT WE ENCOUNTERED STALL BUFFET WAS THAT UPON REACHING FL350 WE WEIGHED AT LEAST 506000 LBS. WE ASKED DISPATCH TO WEIGH CARGO UPON ARR IN NARITA. ALSO NOTIFIED DISPATCH OF SUSPECTED WT ERROR.

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.