What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO DFW DUE TO THE FIGHT CREW REPORTING THAT AFTER TAKE OFF MANAGE SPEED REVERTED TO SELECTED SPEED. SWITCHING AUTO PILOTS ALSO DID NOT SOLVE THE ISSUE. ALL PAGES OF THE FLIGHT MANAGEMENT SYSTEM WERE NOT GIVING ANY PREDICTIONS. THE AIRCRAFT LANDED SAFELY AT DFW WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE #1 FLIGHT MANAGEMENT AND GUIDANCE COMPUTER (FMGC) PER AMM 22-97-00. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.