HDG TRACK DEV DUE TO ACFT EQUIP PROBLEM OPERATING PROCS.

Narrative

WHEN LINED UP ON RWY 13 AT LGA; WE SWITCHED BOTH COMPASSES FROM MAGNETIC MODE TO DIRECTIONAL GYROSCOPE MODE AND ALIGNED COMPASSES WITH THE MAGNETIC HDG OF THE RWY (134 DEGS) (DUE TO STEEL PILINGS UNDER RWY). AFTER TKOF WE FOLLOWED THE NORMAL NOISE ABATEMENT PROCS AND ACCOMPLISHED THE PUBLISHED WHITESTONE CLB PROCS. WE WERE GIVEN A CLRNC TO CLB TO 15000 FT; AND SUBSEQUENTLY A L TURN TO 290 DEGS. AT THIS TIME; AND CLBING OUT OF 5000 FT; WE RETURNED THE COMPASSES TO THE MAGNETIC MODE; AND ROLLED OUT ON A 290 DEG HDG. DURING THE CLB WE NOTICED WE WERE CONVERGING WITH OTHER CLBING TFC AND ASKED DEP ABOUT IT. WE WERE ASKED OUR HDG AND TOLD TO LEVEL AT 10000 FT. IT WAS THEN WE DISCOVERED OUR MAGNETIC COMPASSES DIFFERED FROM THE STANDBY COMPASS BY ABOUT 40 DEGS. DEP GAVE US GYROSCOPE FAILURE TURNS UNTIL WE WERE ABLE TO RETURN OUR MAGNETIC COMPASSES TO NORMAL. SUPPLEMENTAL INFO FROM ACN 224027: IF WE HAD BEEN IMC WITHOUT CAT II; ONLY CTLR VIGILANCE COULD PREVENT CONFLICT/COLLISION HAD CONDITIONS (ACFT PROX AND FLT PROFILE) LED US CLOSER.