MD80 CAPT DID NOT FLY CTLR ASSIGNED HDGS.

Narrative

AFTER TKOF FROM DCA TO THE NW; WE WERE TRACKING THE DCA 328 DEG RADIAL. AFTER HAVING BEEN GIVEN A L TURN TO 150 DEGS; I INADVERTENTLY SELECTED A HDG OF 170 DEGS INSTEAD TO INTERCEPT THE OTT 184 DEG RADIAL (BECAUSE THE SELECTION OF 150 DEGS WOULD HAVE COMMANDED A R TURN ON THE AUTOPLT INSTEAD OF THE L TURN WE WERE CLRED TO MAKE). I FAILED TO RESET THE HDG TO 150 DEGS AND WE SUBSEQUENTLY ROLLED OUT ON A 170 DEG HDG (INSTEAD OF 150 DEGS). THE CTLR LATER WONDERED WHY WE WERE FLYING A 170 DEG HDG INSTEAD OF 150 DEGS (WHICH WOULD NOT INTERCEPT THE OTT 184 DEG RADIAL). HE THEN TURNED US L TO 090 DEGS TO INTERCEPT. HE SEEMED ANNOYED AT OUR MISTAKE. I HAVE LEARNED THAT A TURN ON THE AUTOPLT OF NEAR 180 DEGS CAN CAUSE A PROB LIKE THIS IF I DON'T ESTABLISH THE CORRECT HDG SOON AFTER TURNING SOMEWHAT. THERE WAS NO CONFLICT WITH TFC; AND WE EVENTUALLY INTERCEPTED OUR RADIAL AND CONTINUED OUR CLB TO ALT. THE CTLR SWITCHED US TO A NEW FREQ AND NOTHING MORE WAS SAID. I'M NEW TO THE MD80 AND LEARNED A VALUABLE LESSON HERE.