FMC UPDATING WHEN LNAV ARMED. FLC CONFUSION.

Narrative

PRIOR TO TKOF COPENHAGEN; CAPT AND I DISCUSSED THE ODIN 1C DEP PROC AND MENTIONED THAT THE KASTRUP VOR WAS AT THE FAR END OF RWY 22R AND THE DME WOULD WIND DOWN BEFORE INCREASING AGAIN TO 2.0 FOR OUR R TURN TO 285 DEG HDG. AFTER TKOF; THE GEAR WAS RAISED AND LNAV ARMED. PASSING ABOUT .5 DME THE CAPT NOTED THE MAGENTA LINE WAS BEHIND THE ACFT AND I SHOULD START MY R TURN TO 285 DEGS. I INITIATED MY TURN SLOWLY; POINTING OUT THAT WE WERE NOT YET 2.0 DME. CONFUSED; I STOPPED MIDWAY IN MY TURN. CAPT CONTACTED DEP CTL AND WAS GIVEN A 260 DEG HDG AND TOLD TO CONTINUE CLB TO 8000 FT. HAVING REALIZED OUR EARLY TURN; HE APOLOGIZED FOR OUR DIVERSION FROM THE DEP PROFILE. THE CTLR STATED HE 'WOULD SPEAK TO THE TWR ABOUT IT.' FURTHER DEP INSTRUCTIONS WERE GIVEN; AND NOTHING ELSE WAS SAID ABOUT THE DEV. LESSON LEARNED: BELIEVE THE RAW DATA (DME) ESPECIALLY JUST AFTER TKOF WHEN THE FMC IS STILL TRYING TO UPDATE ITSELF. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ON DOMESTIC FLT; FLCS GENERALLY DELAY ARMING LNAV UNTIL 2000-3000 FT; WHEREAS IN FOREIGN COUNTRIES THEY ARE INSTRUCTED TO ARM LNAV JUST AFTER TKOF. BUT; RPTR SAYS; FOREIGN SID'S AND STAR'S INVARIABLY CALL FOR QUICKER HDG AND/OR ALT CHANGES THAN DOMESTIC OPS. THUS; WHEN ARMING LNAV IMMEDIATELY AFTER TKOF; IT IS LIKELY THAT THE FMC WILL STILL BE UPDATING AND BE INACCURATE. RPTR FOLLOWS RAW DATA ONLY ON THE INITIAL SID PROC IN ORDER TO GIVE THE FMC TIME TO UPDATE. HE ALSO SAYS THAT FMC'S VARY FROM ACFT TO ACFT; SOME UPDATE QUICKER THAN OTHERS. HOWEVER; ALL WILL BE ACCURATE WITHIN A FEW MI AFTER TKOF.