Narrative:

This could be a serious issue. I believe there is a problem with our opc when it calculates crosswind and tailwind data for takeoffs and lndgs. This problem occurs due to the fact it calculates wind components from the runway number and not the runway heading. In most cases these are about the same and it wouldn't present a problem. But consider the following example with actual opc output: mco runways 17L/right and 18L/right both have a magnetic heading of 184 degrees. Winds: 080 degrees at 36 KTS computes to: a 36 KT crosswind for runway 17L/right? Which is out of limits; and a 35 KT crosswind for runway 18L/right? Which is ok. These winds also compute vref/vapp speeds as: runway 17L/right 131/149 runway 18L/right 131/136. In this case; we are adding an additional 13 KTS to vref for approach speeds to one set of runways that are parallel another set. That doesn't make any sense and might not be the safest thing to do. Another example for the same runways in mco: winds: 280 degrees at 36 KTS computes to: a 12 KT tailwind for runway 17L/right; which is out of limits; and a 6 KT tailwind for runway 18L/right; which is ok. Again; parallel runways and one is out of limits and one is not. I don't think the orlando tower controllers would understand why we can land on the west complex runways and not the east complex runways. This example could also occur in dtw (which is where I saw it this last trip). It is much more pronounced in mco due to the fact that runways 17L/right are 14 degrees off from the actual heading. Because of this anomaly; the opc could be telling crews it is acceptable to land and take off when they are really not allowed to due to fom limitations. Or; crews may be diverting due to winds being out of limits when they could actually land. Neither case would be good. Recommendation: I believe we need to change the opc to calculate wind components from the actual runway heading and not the runway 'number/name.'

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Original NASA ASRS Text

Title: A PLT RPTS THE ONBOARD COMPUTER CALCULATES XWIND COMPONENT FROM RWY NUMBER NOT RWY HDG POTENTIALLY CAUSING OUT OF LIMIT LNDGS.

Narrative: THIS COULD BE A SERIOUS ISSUE. I BELIEVE THERE IS A PROB WITH OUR OPC WHEN IT CALCULATES XWIND AND TAILWIND DATA FOR TKOFS AND LNDGS. THIS PROB OCCURS DUE TO THE FACT IT CALCULATES WIND COMPONENTS FROM THE RWY NUMBER AND NOT THE RWY HDG. IN MOST CASES THESE ARE ABOUT THE SAME AND IT WOULDN'T PRESENT A PROB. BUT CONSIDER THE FOLLOWING EXAMPLE WITH ACTUAL OPC OUTPUT: MCO RWYS 17L/R AND 18L/R BOTH HAVE A MAGNETIC HDG OF 184 DEGS. WINDS: 080 DEGS AT 36 KTS COMPUTES TO: A 36 KT XWIND FOR RWY 17L/R? WHICH IS OUT OF LIMITS; AND A 35 KT XWIND FOR RWY 18L/R? WHICH IS OK. THESE WINDS ALSO COMPUTE VREF/VAPP SPDS AS: RWY 17L/R 131/149 RWY 18L/R 131/136. IN THIS CASE; WE ARE ADDING AN ADDITIONAL 13 KTS TO VREF FOR APCH SPDS TO ONE SET OF RWYS THAT ARE PARALLEL ANOTHER SET. THAT DOESN'T MAKE ANY SENSE AND MIGHT NOT BE THE SAFEST THING TO DO. ANOTHER EXAMPLE FOR THE SAME RWYS IN MCO: WINDS: 280 DEGS AT 36 KTS COMPUTES TO: A 12 KT TAILWIND FOR RWY 17L/R; WHICH IS OUT OF LIMITS; AND A 6 KT TAILWIND FOR RWY 18L/R; WHICH IS OK. AGAIN; PARALLEL RWYS AND ONE IS OUT OF LIMITS AND ONE IS NOT. I DON'T THINK THE ORLANDO TWR CTLRS WOULD UNDERSTAND WHY WE CAN LAND ON THE W COMPLEX RWYS AND NOT THE E COMPLEX RWYS. THIS EXAMPLE COULD ALSO OCCUR IN DTW (WHICH IS WHERE I SAW IT THIS LAST TRIP). IT IS MUCH MORE PRONOUNCED IN MCO DUE TO THE FACT THAT RWYS 17L/R ARE 14 DEGS OFF FROM THE ACTUAL HDG. BECAUSE OF THIS ANOMALY; THE OPC COULD BE TELLING CREWS IT IS ACCEPTABLE TO LAND AND TAKE OFF WHEN THEY ARE REALLY NOT ALLOWED TO DUE TO FOM LIMITATIONS. OR; CREWS MAY BE DIVERTING DUE TO WINDS BEING OUT OF LIMITS WHEN THEY COULD ACTUALLY LAND. NEITHER CASE WOULD BE GOOD. RECOMMENDATION: I BELIEVE WE NEED TO CHANGE THE OPC TO CALCULATE WIND COMPONENTS FROM THE ACTUAL RWY HDG AND NOT THE RWY 'NUMBER/NAME.'

Data retrieved from NASA's ASRS site as of January 2009 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.