What was found
ON CLIMBOUT (JUST AFTER LIFT OFF) WE LOST LNAV/VNAV AND FLIGHT DIRECTOR ON BOTH CA + FO DISPLAY. AROUND 1000FT WE LOST AUTHOTHROTTLE. AFTER A FEW TRIES WE REGAINED LNAV ONLY. WE LEVELED 10000 REGAINED A/T THEN LOST IT A SECOND TIME AND WAS UNABLE TO GET IT BACK. WE DECIDED TO RETURN TO LAS AND DECLARE AN EMERGENCY. WE HAD A SMOOTH APPROACH AND NORMAL LANDING. WE DID NOT LAND OVERWEIGHT. WE NEVER GOT THE VNAV BACK. AIRPORT EMERGENCY VEHICLES WERE PRESENT AT LANDING AND FOLLOWED US TO THE GATE.<[01] R&R?D LEFT ADIRU PER AMM 34-21-01 AND R&R?D TAT PROBE PER AMM 34-21-06