FLC OF AN MLG FAILED TO MAINTAIN ASSIGNED ALT DUE TO A MISUNDERSTANDING OF APCH CLRNC GIVEN BY ATC.

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I WAS THE CAPT ON FLT FROM MCI TO ICT. IT WAS A VFR NIGHT AND WE WERE ON A RADAR VECTOR FOR THE ILS FINAL TO RWY 19R. THERE WERE NUMEROUS SMALL ACFT FLYING THAT NIGHT; DUE TO THE NICE WX; SO WE WERE GIVEN A 240 DEG HDG AND A DSND AND MAINTAIN 4000 FT. IT WAS AT THIS TIME (240 DEG HDG; LEVEL AT 4000 FT) THAT THE LOC CAME ALIVE; THE CTLR ASKED US IF WE HAD THE ARPT IN SIGHT. WE ACKNOWLEDGED THAT WE DID AND HE SAID 'PROCEED VIA YOUR OWN NAV FOR THE STRAIGHT-IN APCH.' HE NEVER TOLD US TO MAINTAIN 4000 FT OR TO INTERCEPT AND TRACK INBOUND ON THE LOC IN WHICH WE WOULD HAVE MAINTAIN 4000 FT. HIS TERMINOLOGY WAS SUCH THAT WE BOTH FELT WE WERE CLRED FOR THE VISUAL STRAIGHT- IN VIA OUR OWN NAV. ONCE WE WERE ON THE LOC WITH GS INTERCEPT WE COMMENCED OUR APCH. AT APPROX 3700 FT I GOT A TCASII WARNING OF TFC AT 3600 FT. I GOT A DO NOT DSND. AT THIS POINT I DID HAVE THE TARGET ACFT VISUALLY AND KNEW HE POSED NO THREAT BUT I STILL FOLLOWED THE TCASII COMMAND AND LEVELED THE ACFT AT 3600 FT. THE CTLR THEN ASKED WHAT IS YOUR ALT? WE TOLD HIM 3600 FT; HE SAID MAINTAIN 3500 FT AND THEN TOLD US WE WERE NOT CLRED TO DSND OUT OF 4000 FT. THAT WAS AN OUTRIGHT LIE. HE TOLD US TO PROCEED VIA OUR OWN NAV FOR THE STRAIGHT-IN APCH; IF HE WANTED US TO STAY AT 4000 FT HE SHOULD HAVE STATED THAT OR TOLD US TO TRACK INBOUND ON THE LOC. I AM SICK OF THE FAA ALLOWING CTLRS TO GIVE VAGUE OR MISLEADING CLRNCS AND THEN BACKING THEM AND VIOLATING PLTS. CTLRS SHOULD BE HELD ACCOUNTABLE FOR ALTS THEY WANT ACFT TO BE AT AND SHOULD STATE IT IN PLAIN ENGLISH! IF HE CLRS ME VIA MY OWN NAV; I TAKE THAT TO BE BOTH LONGITUDINAL AND VERT UNLESS STATED OTHERWISE ESPECIALLY WHEN HE SAYS I'M CLRED FOR THE STRAIGHT-IN. VAGUE TERMINOLOGY GETS MORE PLTS IN TROUBLE THAN ANY OTHER THING AND WE CONTINUE TO ALLOW CTLRS TO USE AND GET AWAY WITH THIS WITHOUT CONSEQUENCE WHILE PLTS CONTINUE TO BE UNFAIRLY VIOLATED BECAUSE WE ARE NOT MIND READERS.