HDG TRACK DEV BY WDB ON DEP PROC DUE TO ACFT EQUIP MALFUNCTION PROBLEM.

Narrative

DUE TO MECHANICAL PROBLEMS; THE FIRST ACFT THAT WE WERE SUPPOSED TO FLY HAD TO BE REPLACED BY A SUBSTITUTE ACFT. THE 'NEW' SECOND ACFT WAS TOWED OVER FROM A MAINT HANGAR. WE WERE LATE. THINGS WERE RUSHED; BUT ALL REQUIRED PROCS WERE FOLLOWED BY THE 3 PLT CREW MEMBERS. THE ACFT MAINT LOG HAD SEVERAL 'DEFERRED' ITEMS. THE MOST SERIOUS TO US BEING AN OPEN ITEM THAT THE 'WET' COMPASS WAS UNRELIABLE AND OFF BY AS MUCH AS 20 DEGS. WELL; THE WDB USES 3 SEPARATE INS (INERTIAL REF) SYSTEMS FOR COMPASS STABILIZATION FOR ALL PHASES OF FLT. ALL 3 WERE FUNCTIONING NORMALLY. IN DAY TO DAY OPS THE 'WET' MAGNETIC COMPASS IS RARELY EVER EVEN LOOKED AT SO WE WEREN'T TOO CONCERNED ABOUT THE 'BAD' WET COMPASS WRITE UP. ON THE WDB THE INS SYSTEMS ALIGN THE PLTS COMPASS DISPLAYS (HSI AND RMI) USING MAGNETIC FLUX VALVES LOCATED IN THE WINGS TO SENSE MAG N; AND THEN THE INS SYS USES THE STABILIZED 'TRUE N' INFO FROM THE INS. BOTH OF THESE ARE FED TO THE AIR DATA COMPUTERS (CADC) AND THE SUBSEQUENT MAGNETIC OR TRUE HDG INFO IS DISPLAYED ON THE PLTS RESPECTIVE INSTS (HSI). WITH ALL OF THIS COMPLICATED EQUIP; THE BASIC FINAL CHK BEFORE TKOF IS TO VERIFY THAT HSI AND RMI HDGS AGREE WITH THE HDG OF THE RWY. A VERY SIMPLE XCHK THAT WE ALL FORGOT IN OUR RUSH TO GET GOING SINCE WE WERE LATE DUE TO THE EARLIER MECHANICAL PROBLEMS. (OUR BASIC AIRMANSHIP HABITS LEARNED FROM DAY ONE GOT LOST IN THE HIGH-TECH RUSH OF TODAY'S SYS). WHEN WE TOOK OFF WE DIDN'T NOTICED THAT THE HSI'S WERE NOT YET ALIGNED TO THE PROPER HDG. THEN; (AS FATE WOULD HAVE IT) THE COMPASS SYSTEMS (BOTH!) WERE SHOWING THE WRONG HDGS. THERE WAS THEN A COMPASS SYS MALFUNCTION BUT NO CORRESPONDING FLAGS. THE CAPT'S HSI REPEATS HDG INFO TO THE FO'S RMI AND THE FO'S HSI REPEATS TO THE CAPT'S RMI. WE TURNED TO THE PROPER HDG AS REQUIRED ON THE SID. THEN THE TWR ASKED US WHAT HDG WE WERE ON. THE CAPT'S HSI SHOWED THE APPROPRIATE HDG OF THE SID BUT BOTH RMI'S AND MY HSI SHOWED DIFFERENT HDGS. BUT NO FLAGS. (THIS ISN'T SUPPOSED TO HAPPEN). WE THEN ATTEMPTED TO GET HDG INFO FROM THE MAG (WET) COMPASS BUT WERE AFRAID TO RELY ON IT. SO NOW; WERE READING TRUE N INFO FROM THE INS DISPLAY AND MENTALLY ADDING VARIATION AND WIND DRIFT TO GET AN APPROX CORRECT HDG. AFTER SWITCHING FROM TWR; TO DEP CTL THROUGH 2 SECTORS WE INFORMED THE CTLRS OF OUR SITUATION. WE CONTINUED CLB OUT AND ONCE WE GOT UP TO HIGH ALT THE COMPASS SYSTEMS 'SETTLED DOWN' (EXCEPT THE STILL BROKEN WET COMPASS). THE ENTIRE FLT CONTINUED UNEVENTFULLY. WE CONTINUED BECAUSE OUR RTE WAS GOING TO BE VFR AT DEST (DTW); AND WE DETERMINED THAT ALL 3 INS SYSTEMS WERE OPERATING NORMALLY. IT WAS JUST THE HSI DISPLAYS THAT WERE SUSPECT.