Narrative:

At the time of pushback; sfo weather was rapidly deteriorating; with the airport in the process of changing runways from 28 to 10. As we taxied off the ramp I brought up local radar and noted a gust front approaching sfo with convective activity and rain. During a stop I showed the rest of the crew this web page and predicted that the runways would be changing again before we departed; and shortly afterward the convective line did pass over sfo with strong winds and rain.after frontal passage as we moved onto taxiway zulu toward 10R; I noted that windsocks at uniform and romeo were gusting with what appeared to be near direct tailwinds. I searched for and located a head/cross/tailwind app on the internet; and when I entered the real-time winds as reported by ground was stunned to see how large the tailwind component was for runway 10R/left. I brought this to the attention of the other crew members; and all of us agreed that we were uncomfortable departing with that large a tailwind component and tried to understand how other aircraft were able to. We requested takeoff data with winds from the ATIS and were given marginally acceptable takeoff data for a dry runway; but when we changed the request to a wet runway we received invalid data; and that we could not depart. We discussed using dry runway data; but all of us agreed that that would not be a legal/safe/smart decision since it was still raining and the runway was obviously wet.I am unable to directly quote the winds; but they were rapidly changing moment to moment. If the ATC tapes are no longer available; there are several websites run by aviation hobbyists record and post on the internet recordings of many ATC facilities; it is quite possible sfo the tower and ground communications during this period are available on one of these sites and wind data from them can be determined and used for this report.by the time we reached #1 for takeoff on runway 10R the winds were gusty and shifting; and aircraft coming off the ramp were being directed to runway 28. After discussing it one more time to make sure; we formally refused takeoff with sfo tower and were directed to runway 28R along with the other aircraft; where we safely departed about 15 minutes later.I have the following questions I would like to have answered; or would like to discuss with someone smarter than me:1) when dealing with a cross/tailwind takeoff; how much gust factor should be entered in the runway data request? Should it be worst case; an average; or a trend?2) the fom states that a wet runway is 'a runway is wet when more than 25 percent of the runway surface area within the reported length and width being used is covered by any visible moisture or dampness; and the runway is not contaminated.' if this is taken literally; then almost any amount of precipitation covering more than 25% of the runway would classify it as wet; and require wet runway takeoff data to be used. True? False? Depends? I understand that dampness from a heavy sfo fog is not the same as dampness from a rain event; but where do we draw the line? With the weather conditions at sfo it is hard to believe that a runway could be considered dry when it was actively raining.3) is it possible to have a head/cross/tailwind app put on our ipads? 2018 marks 21 years of 121 aviation; but I was still taken aback by the large tailwind component when the crosswind was entered for the active runway.finally; lately I've been hearing the term 'mission' more and more often regarding our flights. When I hear 'mission;' I think of A-10s flying in support of troops in contact; not an airline flight. My concern is that other flight crews; in the desire to 'complete the mission;' either became task saturated and were not aware of the airport conditions; or deliberately chose to ignore them and departed in a potentially hazardous environment.the intent of this report is not to snitch on other crews who chose to depart that day in that environment; but to find out if the concerns of our crew were valid; or if we were being overly cautious. And if I'm wrong; I want to be told so I can learn and improve. But I'd rather speak up and be seen as the overly cautious guy than miss the opportunity to speak up and draw attention to a dangerous trend of 'accomplish the mission no matter what!' that needs to be broken before we end up with a serious mishap involving loss of life and aircraft.

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Original NASA ASRS Text

Title: Air carrier First Officer reported that the assigned runway for takeoff had a tailwind component that was out of limits for the aircraft.

Narrative: At the time of pushback; SFO weather was rapidly deteriorating; with the airport in the process of changing runways from 28 to 10. As we taxied off the ramp I brought up local radar and noted a gust front approaching SFO with convective activity and rain. During a stop I showed the rest of the crew this web page and predicted that the runways would be changing again before we departed; and shortly afterward the convective line did pass over SFO with strong winds and rain.After frontal passage as we moved onto taxiway Zulu toward 10R; I noted that windsocks at Uniform and Romeo were gusting with what appeared to be near direct tailwinds. I searched for and located a Head/Cross/Tailwind app on the internet; and when I entered the real-time winds as reported by ground was stunned to see how large the tailwind component was for runway 10R/L. I brought this to the attention of the other crew members; and all of us agreed that we were uncomfortable departing with that large a tailwind component and tried to understand how other aircraft were able to. We requested takeoff data with winds from the ATIS and were given marginally acceptable takeoff data for a dry runway; but when we changed the request to a wet runway we received invalid data; and that we could not depart. We discussed using dry runway data; but all of us agreed that that would not be a legal/safe/smart decision since it was still raining and the runway was obviously wet.I am unable to directly quote the winds; but they were rapidly changing moment to moment. If the ATC tapes are no longer available; there are several websites run by aviation hobbyists record and post on the internet recordings of many ATC facilities; it is quite possible SFO the Tower and Ground communications during this period are available on one of these sites and wind data from them can be determined and used for this report.By the time we reached #1 for takeoff on runway 10R the winds were gusty and shifting; and aircraft coming off the ramp were being directed to runway 28. After discussing it one more time to make sure; we formally refused takeoff with SFO Tower and were directed to runway 28R along with the other aircraft; where we safely departed about 15 minutes later.I have the following questions I would like to have answered; or would like to discuss with someone smarter than me:1) When dealing with a cross/tailwind takeoff; how much gust factor should be entered in the runway data request? Should it be worst case; an average; or a trend?2) The FOM states that a Wet Runway is 'A runway is wet when more than 25 percent of the runway surface area within the reported length and width being used is covered by any visible moisture or dampness; and the runway is not contaminated.' If this is taken literally; then almost any amount of precipitation covering more than 25% of the runway would classify it as wet; and require Wet Runway takeoff data to be used. True? False? Depends? I understand that dampness from a heavy SFO fog is not the same as dampness from a rain event; but where do we draw the line? With the weather conditions at SFO it is hard to believe that a runway could be considered dry when it was actively raining.3) Is it possible to have a Head/Cross/Tailwind app put on our iPads? 2018 marks 21 years of 121 aviation; but I was still taken aback by the large tailwind component when the crosswind was entered for the active runway.Finally; lately I've been hearing the term 'Mission' more and more often regarding our flights. When I hear 'Mission;' I think of A-10s flying in support of troops in contact; not an airline flight. My concern is that other flight crews; in the desire to 'Complete the mission;' either became task saturated and were not aware of the airport conditions; or deliberately chose to ignore them and departed in a potentially hazardous environment.The intent of this report is not to snitch on other crews who chose to depart that day in that environment; but to find out if the concerns of our crew were valid; or if we were being overly cautious. And if I'm wrong; I want to be told so I can learn and improve. But I'd rather speak up and be seen as the overly cautious guy than miss the opportunity to speak up and draw attention to a dangerous trend of 'Accomplish the Mission no matter what!' that needs to be broken before we end up with a serious mishap involving loss of life and aircraft.

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.