What was found
(CAN) AFTER BEING AIRBORNE FOR ABOUT 30 MINUTES, CAPTAIN HAD AN INDICATION OF HYDR ISO VALVE, VERIFICATION REVEALED HE HAD LOST ALL THE HYDR FLUID FROM THE NR 1 SIDE. AN EMERGENCY WAS DECLARED AND THE ACFT RETURNED TO BASE. INVESTIGATION BY MX FOUND HYDR TUBE PN DSC 346-1 HAD CHAFED THROUGH UNDER THE CLAMP P/N DSC 337SS10-3. A FLEET CAMPAIGN DIRECTIVE HAS BEEN LAUNCHED TO VERIFY THE REST OF THE ACFT IN OUR FLEET.