This is the date of the "new" Oceanic flight in LA X, as evidenced by the sonogram picture of Aaron that Claire is seen holding towards the end of the episode.
It also happens to be the date that Desmond turned the failsafe key in "Live Together, Die Alone".
Perhaps the turbulence that the LA X Oceanic flight encountered was the beginings of the Locke failing to push the buttom, and so it was Desmond that saved the "new" flight.