What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: DURING CLIMB OUT, CAPTAIN'S PRIMARY FLIGHT DISPLAY ILLUMINATED ON AND OFF WITH SPEED LIMIT, THEN CA'S HORIZONTAL BAR ON FLIGHT DIRECTOR DISAPPEARED AND CAME BACK DURING THE FLIGHT. ALSO, THE MINIMUM SPEED RED AND BLACK BAR SHOWED ON THE CA'S PRIMARY FLIGHT DISPLAY AS IF IT WOULD STALL. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT ORD. REMOVE AND REPALCED CAPTAIN (AOA)-ANGLE OF ATTACK VANE. PER AMM 34-21-05. OPERATIONAL CHECK GOOD, NO ACTIVE FAULTS.