B737-700 SUFFERS TRACK DEV WHEN THE PF DIVERTS HIS ATTENTION TO COMPLETE A PAX PA ANNOUNCEMENT WITH THE ACFT IN A TURN. PNF ATTENTION DIVERTED TO LOG BOOK ENTRIES.

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WE WERE BEING VECTORED DURING OUR DEP CLB AND HAD BEEN ASSIGNED HEADING 325 DEGS. THE PF HAD THE ACFT IN HDG SEL AND VERT SPD MODES. IN THE TURN; PASSING THROUGH APPROX 300 DEGS; WE ENCOUNTERED MODERATE WAKE TURBULENCE FROM A PRECEDING ACFT. WE DID NOT RECOGNIZE AT THE TIME THAT THE FLT DIRECTOR ROLL MODE CHANGED TO CWS FROM HDG SEL AFTER ENCOUNTERING THE WAKE. IMMEDIATELY AFTER THE WAKE TURBULENCE; THE A FLIGHT ATTENDANT CALLED THE CABIN TO SAY THEY WERE HAVING PROBLEMS WITH PAX IGNORING THE SEATBELT SIGN; WHICH WAS ILLUMINATED. THE PF WENT ON THE PA TO BRIEF THE PAX TO SIT DOWN IMMEDIATELY; BECAUSE WE DID NOT KNOW IF WE WOULD ENCOUNTER MORE WAKE TURBULENCE. NEITHER OF US RECOGNIZED THAT THE ACFT WENT PAST THE ASSIGNED HEADING IN CWS MODE UNTIL ATC ISSUED A CORRECTIVE HEADING AND ADVISED 'NO DELAY' ON OUR CLB THROUGH FL260 FOR TFC. WE COMPLIED WITH ATC INSTRUCTIONS AND WERE CLRED BACK ON COURSE BY ATC AFTER WE COMPLIED WITH THEIR CORRECTION HEADING. TOTAL COURSE DEV WAS ABOUT 70 DEGS. NO TCAS TA'S OR RA'S WERE ISSUED. WHILE CLBING OUT IN ADVERSE WX; THE FLT ATTENDANT CALLED THE FLT DECK TO RPT PEOPLE WOULD NOT REMAIN SEATED. AS THE PF; I TOLD THE PM THAT I WAS 'GOING TO BE OFF' TO ADDRESS THE PAX ABOUT COMPLYING WITH FLT ATTENDANT DIRECTIONS. I USED THE 'CAPT'S AUTHORITY' TO DEVIATE FROM FOM PROCS OF PF MAKING A PA. I SHOULD HAVE CLEARLY STATED; 'YOU HAVE THE ACFT.' WHILE MAKING MY PA; I FAILED TO MONITOR THE PROGRESS OF THE ACFT HEADING CHANGE. I STILL BELIEVE IT IS PROPER FOR THE CAPT TO MAKE PA'S AS THE PM; WHEN IT IS TIME CRITICAL FOR SAFETY. BUT WHEN THE PF MAKES A NECESSARY PA TO THE CABIN; HE SHOULD 'CLEARLY STATE' TO THE PM HE IS NOW THE PF INSTEAD OF STATING; 'I'M GOING TO BE OFF.' HAD I DONE THIS; THIS HEADING DEV WOULD PROBABLY NOT HAVE OCCURRED. CLEAR; CONCISE COMMUNICATION WOULD HAVE PREVENTED THIS EVENT.SUPPLEMENTAL INFO FROM ACN 767621: ALSO; WHEN THE PF STARTED THE PA; THE PM SHOULD HAVE SUSPENDED HIS WORK IN THE LOGBOOK TO CONCENTRATE ON MONITORING THE ACFT; WHICH WOULD HAVE ALLOWED HIM TO DETECT THE ERROR.