Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types
Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
When inbound to RKSI and just checking into ICN approach control.  We were filed for the KARBU 1P arrival and ATIS was saying landing Runway 33R and 34; and this arrival is for those runways as well.  ATC on initial contact clears us for KARBU 1N which is for Runway 15 and 16 and he said information X current.  So [the first officer] pulled up new ATIS while I was changing over to KARBU 1 N arrival; all while being over KARBU.  KARBU 1P goes 267 degrees to NOTIN then 231 degrees to SI 857; which is what was in the FMC and we were filed for.  So while I was pulling up KARBU 1N which is KARBU 267 degrees to EGOBA then 266 degrees to SEL; we had a dual FMC failure; autopilot disconnected; auto throttle disconnected; all sorts of EICAS messages and FMC saying timed out standby.  Once we had FMC coming back and could pass along to ATC that we had an FMC navigation problem we did.  Then ATC preceded to put us on a vector and so never flew the arrival and he then said landing Runway 33R.  I believe we were off course due to what was planned and in the FMC and would have had us left of course; due to not being able to get the FMC to change the arrival due to the failure.  After shutdown we wrote up the [FMC] and I spoke with maintenance.
While descending on the karbu1p arrival into RKSI; the controller gave us new arrival instructions. The pilot monitoring was loading the new arrival into the CDU when we experienced a dual CDU failure. At that point we were unable to comply with the controllers instructions. After what seemed like an eternity; the pilot monitoring was able to explain our situation and he issued us a heading. We then were able to recover CDU operation and landed normally.
A B747 flight crew experiences a dual FMC failure while attempting to enter a new arrival per ATC instructions during descent into RKSI. Radar vectors are requested from ATC and received with normal FMC operation regained later in the descent.