LanFranc -
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Flying a 747 at weight 377 tonnes at 249 KIAS clean
will get it to STALL Have you flown a 747...? I flew them from 1989 until 2008. In USA as well.
I would advise YOU to be careful with "opinions" expressed here.
I do not express opinions. I describe what are 747 procedures.
US ATC cannot waive 200/250 speed limits, but read post nš 11 above for exceptions.
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Happy contrails.