SDR 510022783 | Boeing 747-438 Hydraulic power system—hydraulic line failed. During approach, following gear down selection, HYD QTY LOW 4 and HYD PRESS SYS 4 EICAS msgs flagged, with complete loss of No. 4 hydraulic system. The NNC was completed and the landing was uneventful. Preliminary engineering investigation found that a temporary repair fitted to a No. 4 system hydraulic line in the aft cargo area had failed. The temporary repair had been fitted during the preceding transit to address a minor hydraulic leak.