B747-200
Situational Awareness; Training / Qualification
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance
Aircraft; Human Factors; Procedure
After being airborne a couple of hours we noticed an unusual rate of fuel being burned and a higher thrust required to maintain our cruise speed of .84M at our planned weight. When we reached our planned cruise altitude of FL380 our EPR setting was above 1.48 to maintain .84M which should have been lower at our 'planned weight'. We descended to FL360 and still our thrust required to maintain .84M was high. At our planned weight it should have required 1.22 EPR; it instead required 1.37. Our fuel deficit continued to increase so we suspected that there was an error in what our actual weight was. Based on performance requirements we estimated that we were actually 100;000 LBS heavier based on the power/fuel flow required to maintain speed per the OPS. Because the airplane had burned fuel on schedule on the previous two legs flown by this crew we ruled out a performance issue with the aircraft's powerplants; thus reinforcing our suspicion.We relayed this information to Dispatch and the worked out a new flight plan and fuel burn calculations that we would be arriving with approximately 29.0 FOB [Fuel On Board] and; if a diversion was necessary; at our alternate with only 14.0. We continued on our flight and repeatedly requested updates on our destination weather while keeping Dispatch in the loop on our fuel situation. Our main concern was that fuel would be a serious problem if we had to go to our alternate. Our fuel deficit continued to worsen so that by the time we arrived at our destination we landed with just 22.8 FOB. Our planned fuel burn was 135.9 and our actual fuel burn had been about 168.0. We calculated our landing performance card based on our suspected 100;000 LBS heavier weight and the aircraft performed normally; maintaining a proper 3.5 degree pitch attitude on the ILS approach with the amended bug settings. The weather was approximately 400-500 broken with visibility 1.5 miles on arrival. We were originally supposed to land with 41.1 FOB if our weight was correct. The individual responsible for overseeing the weighing of the freight and making sure that the information is accurately recorded should be more diligent. The error of not accurately recording the weights affects aircraft performance and can cause an unsafe operation.
A B747-200 flight crew noted their fuel burn and thrust required to maintain flight planned altitudes and cruise Mach were excessive and suspected the flight plan and fuel required had been based on faulty load planning data.