SMA X CLB TO OCCUPIED ALT HAD LTSS FROM SMT Y. SYS ERROR.

Narrative

SMA X DEPARTED LBE ARPT; SWBOUND; ASSIGNED RWY HDG AND CLBING TO 4000 FT. SMT Y WAS NWBOUND; LEVEL AT 5000 FT; DEVIATING AROUND WX. SHORTLY AFTER X WAS RADAR IDENTED; HE REQUESTED DIRECT MGW. THE CTLR ISSUED DIRECT MGW AND STATED 'MAINTAIN 5000 FT.' THIS ALT ERROR WAS MISSED WHEN THE PLT READ BACK 'DIRECT MGW; 5000 FT.' THE DATA BLOCK ASSOCIATED WITH X DISPLAYED AN INTERIM ALT OF 4000 FT. FOR THIS REASON; THE CONFLICT ALERT WAS NOT ACTIVATED UNTIL SEPARATION WAS LOST. JUST BEFORE THIS TIME; X BEGAN TO QUESTION HIS CLRNC TO 5000 FT. THE CTLR TOOK IMMEDIATE ACTION BY REASSIGNING 4000 FT. HOWEVER; SEPARATION WAS LOST. RECOMMENDATION: ERROR WAS THE RESULT OF THE CTLR TRANSPOSING ASSIGNED ALTS. ACFT WAS TOLD TO 'MAINTAIN 5000;' NOT 'CLB AND MAINTAIN 5000 FT.' ACFT READ BACK '5000 FT;' THEN COMMENCED TO CLB AND MAINTAIN 5000 FT. CTLR ERRED; THINKING HE ASSIGNED THE ACFT TO MAINTAIN 4000 FT. THE INFO IN THE DATA BLOCK AND POSTED ON THE STRIP REINFORCED THIS BELIEF. SOLUTION: SAY WHAT YOU INTEND TO SAY. BE SURE TO 'HEAR' WHAT IS SAID WHEN LISTENING TO READBACKS.