Following departure from Omaha, hydraulic difficulties were experienced. The flight continued to Denver, using flight manual procedures. Upon arrival near Denver, the ejectors were extended hydraulically, but the hydraulic pressure dropped to zero when an attempt was made to extend flaps to 25 degrees. The hydraulic system selector was then placed in the no. 3 position (flap and gear downlock) and the approach was continued. After touchdown the throttles were placed in the idle reverse thrust position and power was applied. An uncontrollable deviation from the runway occurred and the aircraft crashed into a new taxiway construction. The undercarriage was torn off and the DC-8 caught fire and burned. PROBABLE CAUSE: “The Board determines the probable cause of this accident was the asymmetric thrust which, during a hydraulic emergency, resulted from failure of the thrust reversers on engines nos. 1 and 2 when reverse thrust was selected. A contributing factor was the failure of the first officer to monitor the thrust reverse indicator lights when applying reverse thrust.”