AN A320 PIC TURNS L TO 230 DEGS AFTER TKOF FROM ORD RWY 32R AFTER HIS FO MISTAKENLY READS BACK 'L HDG 230' VICE 'TURN L 320 DEGS' TO TWR CTLR.

Narrative

AFTER TKOF; ATC GAVE US A 3 INSTRUCTION CLRNC: TURN L 320 DEGS; CLB TO 13000 FT; AND CONTACT ORD ON XYZ FREQ. I WAS PF AND NEW CAPT ON THE A320. FO READ BACK ALL CORRECT EXCEPT THE HDG; WHICH HE REPEATED AS 230 DEGS; AND DIALED INTO THE HDG SELECTOR. I WAS IN A HIGH WORKLOAD PHASE AND MISSED THE ATC ASSIGNED HDG OF 320 DEGS. THE FO WAS SURE OF HIS CLRNC READBACK; SO I DECIDED TO FOLLOW THE FLT DIRECTOR/EFIS TO A HDG OF 230 DEGS. TURNING THROUGH ABOUT HDG 270-280 DEGS; ATC SAID VERIFY YOU'RE INTO A TURN OF 320 DEGS; WHICH I QUICKLY DID. WE WERE NOT TOLD OF ANY TFC CONFLICT. WHEN A RADIO CALL IS MISSED; IT'S SO EASY TO JUST GO WITH WHAT THE OTHER PLT HEARD; RATHER THAN GET A VERIFICATION FROM ATC. THIS WORKS 99-100% OF THE TIME; BUT IS FOOLISH AND I KNOW BETTER. AT BUSY ARPTS LIKE ORD IT COULD BE LETHAL. CONTRIBUTING FACTORS FOR THIS ARE MY NEW ASSIGNMENT TO THIS ACFT; OUR COMPANY POLICY OF SAYING OUT LOUD FMA CHANGES BELOW 300 FT ASL (VERY DISTRACTING TO ATC RADIO CALLS); LESS THAN 4-5 HRS SLEEP BEFORE OUR EARLY DEP.