I'm pretty sure it was intended to help prevent accidents like the SQ one in TPE. The problem is that some countries, notably China, use different (outdated?) GPS datums to the FMC database, causing spurious FMC Runway disagree messages. Consequently, some airlines are in the practice of inhibiting GPS updating during take-off to avoid the spurious messages.
Last edited by BuzzBox; 21st September 2012 at 06:45.