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B777 flight crew reported a greater than planned fuel burn on an international flight resulting in a diversion. Further investigation revealed the drag factor in the flight planning software was incorrect.
| Attributes | |
| ACN | 1447950 |
| Time | |
| Date | 201705 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZZ.Airport |
| State Reference | FO |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B777 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Route In Use | Oceanic |
| Flight Plan | IFR |
| Person 1 | |
| Function | Captain Pilot Flying |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Total 5687 Flight Crew Type 2553 |
| Person 2 | |
| Function | Pilot Not Flying First Officer |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 144 Flight Crew Type 224 |
| Events | |
| Anomaly | Deviation - Procedural Published Material / Policy Inflight Event / Encounter Fuel Issue |
Narrative:
I expected a marginal extra fuel burn when I (together with the concurrence of my dispatcher) increased the cost index to 200 from 20 in order to make up some lost time. After two hours enroute on a nearly fourteen hour flight; it became very clear that the overburn was far more than expected. In the next four hours we flew the flight plan exactly as published (cost index; altitude and airspeed) only to find that the overburn continued to be quite large. Each segment of the flight plan produced an additional five hundred pounds of overburn. By the time we were roughly 6 hours into the flight; we were nearly five thousand pounds down on the fuel score. We accomplished the fuel leak procedures (no fuel leak noted) and viewed the output of the engines with our onboard camera (no unusual visuals noted). We elected to make a technical stop in ZZZZ for fuel and had ZZZZ maintenance do all applicable checks. Nothing found. We continued to ZZZZ1 uneventfully.after investigation by flight management; it was discovered that the drag factor the flight planning software used was in error. It was set to 0.4% as opposed to 2.7%
Original NASA ASRS Text
Title: B777 flight crew reported a greater than planned fuel burn on an international flight resulting in a diversion. Further investigation revealed the drag factor in the flight planning software was incorrect.
Narrative: I expected a marginal extra fuel burn when I (together with the concurrence of my dispatcher) increased the Cost index to 200 from 20 in order to make up some lost time. After two hours enroute on a nearly fourteen hour flight; it became very clear that the overburn was far more than expected. In the next four hours we flew the flight plan exactly as published (cost index; altitude and airspeed) only to find that the overburn continued to be quite large. Each segment of the flight plan produced an additional five hundred pounds of overburn. By the time we were roughly 6 hours into the flight; we were nearly five thousand pounds down on the fuel score. We accomplished the fuel leak procedures (no fuel leak noted) and viewed the output of the engines with our onboard camera (no unusual visuals noted). We elected to make a technical stop in ZZZZ for fuel and had ZZZZ maintenance do all applicable checks. Nothing found. We continued to ZZZZ1 uneventfully.After investigation by flight management; it was discovered that the drag factor the flight planning software used was in error. It was set to 0.4% as opposed to 2.7%
Data retrieved from NASA's ASRS site 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.