MD88 FLC FAILS TO MAINTAIN SPD RESTR FOR SPACING.

Narrative

OUR MD88 WAS ENRTE FROM CINCINNATI TO DETROIT. ON CLBOUT PASSING ABOUT 12000 FT; THE CTLR TOLD US TO MAINTAIN 280 KTS FOR SPACING. I PUT 280 KTS IN THE FMS CLB PAGE AND THE ACFT VV1 INCREASED TO LOSE THE AIRSPD. WE WERE TO CRUISE AT ONLY 21000 FT AND WHEN WE REACHED THE ALT; WE HAD SWITCHED CTLRS AND I WRONGFULLY ASSUMED THEY NO LONGER NEEDED THE SPD UNTIL THE NEW CTLR (ZID) ASKED US TO TURN 20 DEGS L FOR SPACING. I CHKED THE AIRSPD AND FOUND THE ACFT ACCELERATING TOWARDS 320 KTS BECAUSE I HAD NOT ENTERED 280 KTS IN THE CRUISE PAGE OF THE FMS. THE FMS WENT TO 'ECON CRUISE' UPON LEVEL OFF AND WE ACCELERATED PAST 280 KTS. I ASKED THE CTLR IF HE STILL NEEDED THE SPD AND HE SAID OF COURSE HE DID. WE SLOWED BACK TO 280 KTS AGAIN AND WERE SUBSEQUENTLY CLRED BACK ON COURSE. UNDOUBTEDLY I CAUSED THE PROB BY PUTTING THE SPD ONLY IN THE FMS CLB PAGE ASSUMING IT WOULD BE DELETED BY THE TIME WE GOT TO CRUISE. SINCE WE WERE ONLY AT FL210; CRUISE CAME SOONER THAN NORMAL AND WE STILL WERE RESTR. THE CTLR DID A GOOD JOB RECOGNIZING OUR DECREASING SEPARATION AND GIVING US THE SPACING VECTOR. IN THE FUTURE; I SHOULD PUT THE RESTR IN THE AIRSPD OVERRIDE PORTION OF THE FMS AND NOT JUST ON THE CLB PAGE; OR IF I DO USE THE CLB PAGE; I SHOULD ALSO INPUT THE SPD INTO THE CRUISE PAGE.