During our prolonged flight back from Belize on the last such trip (we got delayed at Washington when the 28V power plug was ripped out of the fuselage by the handling agents along with the port u/c door strut!) we got bad icing IIRC somewhere between Iceland & Greenland, similar story as above, lots of (diminishing) power & the Atlantic coming closer by the second. Not sure at what altitude it happend (blinking low though!) there was a series of very audible thumps as the ice departed wings, intakes & every other exposed bits, plus a collective sigh from those of us in the back & a resumption of the never ending game of bridge
