TAF SAEZ 302200Z 3100/3124 08005KT 8000 SCT020 BKN050
TX21/3118Z TN10/3109Z
BECMG 3103/3106 VRB03KT 4000 BR SCT010
PROB30 TEMPO 3108/3111 0900 BCFG SCT008
BECMG 3113/3116 35006KT 9999 SCT030=
This would have been the TAF at take off (not briefing) Landing time is about 11:00 UTC (13 hour flight)
Remember that LHR CAT I required vis is 550m and the TAF is giving patches of fog (as explained previously) in a slowly strengthening northerly wind of 900m I can't remember off the top of my head what the CAT I rvr is but 900m ain't too bad. Prob 30 does NOT have to be taken into account for the purposes of fuel planning but judging from the fact they could hold for 25 minutes they certainly did take it into account. LH, long range often does not have the luxury of hours of holding fuel purely due to max take off weight limitations.
TAF SAEZ 301600Z 3018/3118 35005KT 9999 SCT030 SCT040
TX22/3118Z TN12/3110Z
BECMG 3101/3103 VRB02KT 9999 SCT040
TEMPO 3107/3111 3000 BR SCT025
PROB30 3108/3111 0900 BCFG SCT010
BECMG 3111/3113 9999 SCT040
BECMG 3116/3118 36005KT=
This would have been the TAF used for briefing. Again, Prob 30 900m in fog patches, improving. Not a problem. The aircraft would have been loaded to max t/o weight I'm assuming and the max available fuel loaded as well. I've flown this route several times and there is often no/little available weight for fuel (1 or 2 tonnes=20 minutes less the burn needed to cart it to Argentina = 10 minutes extra!)
Both of these TAF's show that the forecast was inaccurate/inadequate and the crew based their fuel decision on a forecast that showed and acceptable weather pattern at arrival.
25 minutes holding after a max range flight was pretty good and definately showed that they had loaded contingency to the max, all IMHO of course.
These guys were just plain unlucky that the fog stirred up unexpectedly (see the forecasts) to 100m or so at the time they were there!