It translates simply as 'God is great'.
The documents recovered from that mass murderer Attas car in Boston contained the instruction to his accomplices of 9-11 to 'shout the words ALLAH AKHBAR' as you take over the aircraft, as these words strike terror into the hearts of the infidels'.
Seems like the CSA hijacker had similiar ideas.
Now, how the f**k did he get on board with a weapon!!