AD FAA-2006-26726

We are adopting a new airworthiness directive (AD) for certain Boeing Model 747-400F and -400 series airplanes. This AD requires installing drains and drain tubes to eliminate water accumulation in the dripshield above the M826 Card File in the main equipment center. This AD results from a report that water from the dripshield entered the card file and damaged a circuit card, causing the AFT CARGO FIRE MSG message to be illuminated and resulting in an air turn back. We are issuing this AD to prevent water from entering the card file and damaging a circuit card. Failure of one or more of the 15 fuel system circuit cards in the card file could cause loss of fuel management, which could cause unavailability of fuel. Failure of one or more of the 35 fire detection circuit cards could cause a false message of a fire, or no message of a fire when there is a fire.