AN ACR B727 HAD LTSS WITH AN ACR B757 APCHING MIA. ALL 3 CREW MEMBERS INSIST THAT THEY WERE GIVEN 4000 FT VICE THE 10000 FT THAT APCH SAID THAT THEY WERE GIVEN. READBACK HEARBACK.

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WE WERE TOLD TO DSND TO WHAT WE THOUGHT WAS 4000 FT. THE CAPT READ BACK 4000 FT AND SET THAT ALT IN THE ALT ALERTER. DSNDING THROUGH 5400 FT; THE CTLR TOLD US HE HAD GIVEN US 10000 FT AND TO CLB TO 8000 FT THROUGH 5700 FT. THE CTLR TOLD US TO LEVEL OFF AT 6000 FT AND MAKE AN IMMEDIATE L TURN. WE THEN HAD VISUAL CONTACT WITH A B757 THAT PASSED ABOVE US. I BELIEVE FATIGUE PLAYED SOME PART. MY RADIO'S VOLUME WAS ALSO VERY LOW BECAUSE IT WAS VERY LOUD TO THE PLTS IF TURNED UP AT ALL; SO I MAY HAVE MISSED WHAT THE CTLR HAD SAID AND THEREFORE WAS UNABLE TO BACK UP THE PLTS PROPERLY. SUPPLEMENTAL INFO FROM ACN 339690: A B757 TOOK EVASIVE ACTION BY DIVING. ALL 3 CREW MEN WERE EXTREMELY FATIGUED; AND HAD FLOWN ALL NIGHT. WE HAD A MALFUNCTIONING AUTOPLT. RADIO PANEL WAS INADEQUATE! SUPPLEMENTAL INFO FROM ACN 340014: WE ALL FORGOT SPDBRAKE AND HAD DIFFICULTY CLBING FROM 5800 FT TO 6000 FT. WE CALLED MIA TWR ON PHONE LATER. SUPVR SAID WE WERE ASSIGNED 10000 FT; READ BACK 4000 FT; AND CTLR DID NOT CATCH ERRONEOUS READBACK. CAPT AND FO CANNOT UNDERSTAND HOW 'ONE-ZERO THOUSAND FT' OR EVEN '10000 FT' CAN SOUND LIKE '4000 FT.' SO DID NOT HEAR ATC XMISSIONS. AIRPLANE HAS NON STANDARD AUDIO PANEL THAT DOES NOT PERMIT SUFFICIENT LATITUDE IN INDIVIDUAL HEADSET VOLUME ADJUSTMENTS. HAD HE BEEN ABLE TO HEAR; HE MIGHT HAVE BEEN ABLE TO CORRECT PLTS' MISUNDERSTANDING OR CONFIRM '4000 FT.'