THE LGA MAGNETIC DISTURBANCE CAUSED A TRACK DEV.

Narrative

WE WERE CLRED INTO POS AND HOLD; RWY 13 AT LGA; WITH THE ADDED INSTRUCTION; 'BE READY FOR IMMEDIATE.' THERE WAS AN APCHING ACFT ON FINAL. MY RMI READ APPROX RWY HDG. HOWEVER; MY ND DISPLAY SHOWED 030. CONFIDENT OF THE WX AND THINKING I HAD ONE GOOD HDG SYS AND NOT WANTING TO CAUSE A MISSED APCH; WE TOOK OFF. SHORTLY AFTER LIFTOFF; I GLANCED AT THE FO'S ND; AND WAS SURPRISED TO SEE THAT I DID NOT AGREE WITH MY RMI. TWR HAD; JUST PRIOR TO BRAKE RELEASE; DIRECTED A TURN AFTER TKOF TO 090; ALTHOUGH WE HAD BEEN ORIGINALLY CLRED THE WHITESTONE CLB AND BRIEFED THE SAME (A R TURN TO 175). I REALIZED AT THIS POINT THAT OUR HDGS WERE NOT INDICATING CORRECTLY; AND IN THE CONFUSION WE INADVERTENTLY MADE A R TURN TO 090 ON THE FO'S ND. APCH CTL THEN BEGAN TO GIVE US VECTORS TO THE L; WHICH WE ATTEMPTED TO FOLLOW BY USING THE SYS OF MIRRORS TO VIEW THE MAGNETIC COMPASS. THIS DID NOT WORK EXTREMELY WELL; BUT KEPT US IN THE GENERALLY CORRECT DIRECTION. THIS PROB WAS CAUSED BY THE OVER-SENSITIVITY OF THE HDG SYS TO THE METAL IN THE RWY AT LGA. IT WAS AGGRAVATED BY THE FACT THAT WE APCHED THE RWY ON THE CLOSEST PARALLEL TXWY; AND WE EXPERIENCED AN APPROX 20 MIN DELAY WAITING FOR TKOF. THE MD88 SHOULD BE EQUIPPED WITH A MAGNETO COMPASS WHICH IS MUCH MORE EASILY ACCESSIBLE AND USEABLE.