CAPT OF AN MLG TURNED THE WRONG WAY WHEN GIVEN A HEADING CHANGE BY ATC AND THEN SUBSEQUENTLY LOST ALT WHEN HE ROLLED BACK INTO A STEEP BANK TURN IN THE OPPOSITE DIRECTION. IN THE MEANTIME THE FO TURNED OFF THE XPONDER MOMENTARILY WHEN HE NOTICED THE CAPT HAD LOST 500 FT ALT.

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LEVEL AT 9000 FT OVER CLEVELAND ARPT. CTLR ISSUED SEVERAL TURNS TO US FOR VECTORS; SOME BEING 210-270 DEGS OF TURN. CTLR ISSUED INSTRUCTION TO TURN 'R HDG 020 DEGS.' CAPT WAS FLYING ACFT ON AUTOPLT. HE INITIATED TURN TO THE L (HE THOUGHT CTLR HAD SAID 320 DEGS). I TOLD HIM ATC WANTED R TURN TO 020 DEGS. HE THEN DISCONNECTED AUTOPLT AND INITIATED R TURN. HE OVERBANKED (TO APPROX 45 DEGS) AND STARTED DSNDING. I SAID; 'WATCH YOUR ALT!' HE QUICKLY REALIZED WHAT WAS HAPPENING AND ARRESTED THE DSCNT AT 8500 FT AND CLBED BACK UP TO 9000 FT; AND ROLLED OUT OF THE BANK ON PROPER HDG OF 020 DEGS. AT THE MOMENT I REALIZED HE WAS LOSING ALT I TURNED THE XPONDER OFF; AND THEN TURNED IT BACK ONCE AT 9000 FT. THE CTLR NEVER SAID ANYTHING ABOUT THE ALTDEV; AND THE REST OF THE FLT WAS UNEVENTFUL. CONTRIBUTING FACTORS: THE CONSTANT HEADING CHANGES BY ATC BROUGHT SOME FRUSTRATION WHICH CAUSED THE CAPT TO SWITCH OFF AUTOPLT AND THEN POSSIBLE LACK OF ATTN TO 'SCAN.' (WE SHOULD HAVE KEPT AUTOPLT ON.) AS I REFLECTED ON MY ACTION (IE; TURNING OFF XPONDER); I'M NOT SURE THAT WAS A GOOD IDEA; MAINLY BECAUSE IT ALSO RENDERS TCASII INOP; AS WELL AS ALT ENCODING.