Narrative:

After passing fmn VOR at FL280 and upon entering an area of showers, we requested and received a climb to FL310 and then to FL350. Gross weight was 126500 pounds and the pms (performance management system) computer indicated a climb capability to FL355 and that this was the optimum altitude for our gross weight and conditions. Engine and wing anti-ice were on during the climb. Aircraft was being flown on autoplt in the 'perf' mode (pms was controling the autoplt). Passing FL320 denver center requested that we be level at FL350 in 6 mins. Aircraft was climbing less than 500 FPM so 'maximum climb' was selected on the pms. Maximum climb mach was .645 and aircraft climbed faster as airspeed bled down from mach .76 to mach .645. Aircraft broke out of WX at FL340 and engine/wing anti-ice and tail de-ice was cycled and turned off. IAS at level off at FL350 was 230 KTS. With climb power selected (mct was less than cl), aircraft would not accelerate and began to gradually lose airspeed. An immediate descent was requested. Denver initially denied the request because of conflicting traffic 2000' below us. We again requested an immediate descent and were given a clearance to FL310 and a turn away from the traffic at FL330. Descent to FL310 was continued with no further problems. Upon landing, a discrepancy was entered into the aircraft logbook describing the above events and requesting that a check be made of the aircraft weight, cargo weight, and distribution to determine why the aircraft would not accelerate at the assumed weight in the pms computer based on the ZFW given to us in the load closeout. Since we had checked our altitude charts, pms computer entries, and passenger count, we determined that we should have been able to hold FL350 at weights up to 130000 pounds.

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Original NASA ASRS Text

Title: FLT REQUESTED FL350 FOR SMOOTHER RIDE. GRANTED BUT UNABLE HOLD AIRSPEED AT FL350 FORCED TO DRIFT DOWN. CENTER GAVE TURN AWAY FROM TRAFFIC AND GAVE TRAFFIC BELOW A TURN TO ACCOMODATE SECOND REQUEST FOR FL310.

Narrative: AFTER PASSING FMN VOR AT FL280 AND UPON ENTERING AN AREA OF SHOWERS, WE REQUESTED AND RECEIVED A CLB TO FL310 AND THEN TO FL350. GROSS WEIGHT WAS 126500 LBS AND THE PMS (PERFORMANCE MGMNT SYS) COMPUTER INDICATED A CLB CAPABILITY TO FL355 AND THAT THIS WAS THE OPTIMUM ALT FOR OUR GROSS WEIGHT AND CONDITIONS. ENG AND WING ANTI-ICE WERE ON DURING THE CLB. ACFT WAS BEING FLOWN ON AUTOPLT IN THE 'PERF' MODE (PMS WAS CTLING THE AUTOPLT). PASSING FL320 DENVER CTR REQUESTED THAT WE BE LEVEL AT FL350 IN 6 MINS. ACFT WAS CLBING LESS THAN 500 FPM SO 'MAX CLB' WAS SELECTED ON THE PMS. MAX CLB MACH WAS .645 AND ACFT CLBED FASTER AS AIRSPD BLED DOWN FROM MACH .76 TO MACH .645. ACFT BROKE OUT OF WX AT FL340 AND ENG/WING ANTI-ICE AND TAIL DE-ICE WAS CYCLED AND TURNED OFF. IAS AT LEVEL OFF AT FL350 WAS 230 KTS. WITH CLB PWR SELECTED (MCT WAS LESS THAN CL), ACFT WOULD NOT ACCELERATE AND BEGAN TO GRADUALLY LOSE AIRSPD. AN IMMEDIATE DSNT WAS REQUESTED. DENVER INITIALLY DENIED THE REQUEST BECAUSE OF CONFLICTING TFC 2000' BELOW US. WE AGAIN REQUESTED AN IMMEDIATE DSNT AND WERE GIVEN A CLRNC TO FL310 AND A TURN AWAY FROM THE TFC AT FL330. DSNT TO FL310 WAS CONTINUED WITH NO FURTHER PROBS. UPON LNDG, A DISCREPANCY WAS ENTERED INTO THE ACFT LOGBOOK DESCRIBING THE ABOVE EVENTS AND REQUESTING THAT A CHK BE MADE OF THE ACFT WEIGHT, CARGO WEIGHT, AND DISTRIBUTION TO DETERMINE WHY THE ACFT WOULD NOT ACCELERATE AT THE ASSUMED WEIGHT IN THE PMS COMPUTER BASED ON THE ZFW GIVEN TO US IN THE LOAD CLOSEOUT. SINCE WE HAD CHKED OUR ALT CHARTS, PMS COMPUTER ENTRIES, AND PAX COUNT, WE DETERMINED THAT WE SHOULD HAVE BEEN ABLE TO HOLD FL350 AT WEIGHTS UP TO 130000 LBS.

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.