LTSS BTWN COMMUTER AND MIL TRANSPORT AFTER UNCOORD PENETRATION OF ADW ATA AIRSPACE. OPERATIONAL ERROR.

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ON APCH INTO DCA ABOUT 15 MI OUT AND APCHING VICINITY OF ANDREWS AFB. DCA APCH CLRED US FROM 6000 FT TO 2000 FT. MY CAPT ACKNOWLEDGED DSCNT AND I STARTED DOWN AT 1000 FPM. THERE WAS ANOTHER COMPANY FLT (Z) WITH A SIMILAR CALL SIGN THAT THIS CTLR HAD PREVIOUSLY CLRED TO 2000 FT. WHEN LEVEL AT 2000 FT WE WERE ASKED 'OUR CALL SIGN; WHAT DO YOU BELIEVE YOUR LAST ASSIGNED ALT WAS?' MY CAPT REPLIED WITH ASSERTION ' OUR CALL SIGN; WE'RE AT 2000 FT AS ASSIGNED;' OR SIMILAR WORDS TO THAT EFFECT. THE CTLR SAID; 'TURN R TO 320.' I SAW AN AIR FORCE TRANSPORT JET Y GO UNDER AND R OF US (ON APCH TO ANDREWS) ABOUT LEVEL 1000 FT BELOW OUR FLT PATH. BOTH OF US HEARD 2000 FT AS AN ASSIGNED ALT FOR OUR ACFT X. I BELIEVE THE CTLR WANTED US AT 3000 FT; NOT 2000 FT; BUT HAD 2000 FT ON HIS MIND; AS HE HAD CLRED COMPANY FLT; Z; TO 2000 FT PREVIOUSLY. IN ANY CASE THE READBACK ACKNOWLEDGEMENT; THE LAST CHANCE TO CORRECT A MISUNDERSTANDING; WAS HEARD AND ACCEPTED WITHOUT COMMENT BY OUR CTLR. MY CAPT ASKED IF HE SHOULD CALL IN THE GND AND THE CTLR SAID 'NO PROBLEM.' I THINK THERE MAY BE A PROBLEM OR I WOULDN'T BE SENDING THIS IN.