I assume it is just map shift you are talking about. As far as I know on aircraft that use an IRS/INS, over time away from any nav radio sources i.e. over the pacific/atlantic the IRS assumed position can drift away marginally from actual position. On the 767 at leasst, if the nav radio's are set to auto, and there is a suitable VOR/DME, the FMC will update it's position with regards to that.
I know the 767 can suffer from map shift as it has no GPS, therefore I assume the 757 can have map shift occur...777 has GPS also, so guess it doesn't have a problem..I don't know if the 747-400 has a GPS hooked up to the FMC or not as standard.
However I could be talking complete rubbish also, as I am only a wannabe..
Cheers,
Tom.
[ 02 September 2001: Message edited by: tom775257 ]