B747 Undifferentiated or Other Model
Flight Crew Last 90 Days 200; Flight Crew Total 14000; Flight Crew Type 4000
Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Aircraft; Company Policy
This report is not specific to the flight listed above; but to all flights I've flown in the last month; indeed; all 747 flights in the last month. Perhaps all Sabre Flights in the last month. Information was issued to the pilots of this fleet in our preflight paperwork in January 2013. This bulletin incorrectly describes the anomaly related to the Sabre Takeoff Performance Wind Direction/Speed calculations. The Note in the bulletin states that if the wind direction/speed is left blank; the takeoff performance data winds are based on the latest hourly observation and are accurate. This is incorrect; and has been incorrect since the issuance of this bulletin. I reported to our fleet the exact anomaly: the hourly data winds reported on the Sabre Takeoff Performance calculations; when left blank; are also subject to the anomaly that is stated on the bulletin relating to manually inserted winds. The magnetic variation at the airport is being applied to the hourly observation and is being applied to the Sabre Takeoff Performance Data on ACARS. For example; if hourly reported winds are 070/05. If the wind direction/speed is left blank as suggested by the bulletin; the Sabre Takeoff Performance Data will return a Takeoff Data message with wind of 053/05 [17 degrees declination]; returning incorrect thrust setting and V speed data to the flight crew. Worldwide; hourly reported winds are reported in 10 degree increments. Upon further study; and multiple opportunities to validate the calculations; Sabre is indeed applying the difference between true and magnetic headings in its calculations. When the wind direction speed is left blank; it is returning erroneous data. I have validated the difference between declinations in Sabre reported winds at [several airports.] This is especially concerning because there are many circumstances in which tailwind data is NOT being calculated; and therefore there are flights departing airports worldwide utilizing incorrect power settings and incorrect V speeds. Indeed; when this anomaly was discovered and investigated after takeoff; we had taken off with an incorrect power setting and V speeds as a result of this anomaly. Two weeks after initially reporting this anomaly; another anomaly has been recognized and previously reported. The Landing Performance Data is subject to the same exact anomaly. Landing Performance Data is not accurate and incorrect runway length requirements are being communicated to the flight crew. As a note which was also communicated: This anomaly can be fixed by the flight crew utilizing some simple common sense; the ONLY way to get accurate wind data out of the ACARS for Sabre Takeoff and Landing Data is to apply the declination between True and Magnetic to the winds and manually input the corrected winds into the ACARS. For example; today; on taxi out; winds were reported 080/05. ACARS Sabre Data (with wind data left blank) returned computed data with winds as 063/05. (Again; the declination at 17 degrees difference between True and Magnetic). For a west declination of 8 degrees; subtract the declination of 8 degrees from the reported winds and insert this number into the wind/speed location in the Takeoff or Landing Data request. Example; reported winds; 030/10. Insert 022/10 and the message will return 030/10 data. A manually inserted wind of 097/05 returned accurate Takeoff data for the winds as reported by tower; actual tailwinds greater than what was reported in the blank Takeoff Data message. One may reasonably ask: What makes the writer think that Sabre is correctly adjusting the Takeoff Data based on the wind input by the writer? It was validated by these means: checking the crosswind component of the returned ACARS data. When the Runway heading and wind direction are matched; the crosswind component disappears. BOTTOM LINE: Why does it take more than a month to simply correctly communicate the real performance problems to our pilots? I can imagine that there are IT department delays on implementing the corrections; but I find it quite ridiculous that we put our crews in jeopardy this way. Somewhere; right now (unless something has changed since I've been on my layover) there is a crew (and most likely all other fleets using Sabre) taking off or landing with incorrect thrust settings and V speed settings.
Air Carrier First Officer reports that the Sabre software used by his company is incorrectly attempting to convert reported winds to magnetic by applying the local declination; when the reported winds are already magnetic.