A DEP MD-80 EXPERIENCES COMPASS/HSI PROBS WITH BOTH COMPASSES DRIFTING LEFT FROM 30 TO 50 DEGS DURING TKOF FROM RWY 13 FOR THE LGA 9 DEP AT LGA; NY.

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TKOF AT LGA RWY 13. LONG DELAY (APPROX 30 MIN) NEAR APCH END RWY 13. POTENTIAL FOR COMPASS PROBS DUE TO PIER. DURING LINE-UP AND TKOF BOTH COMPASSES OK. UPON INITIAL TURN TO 180 DEG (WHITESTONE CLB) FLT DIRECTOR STARTED TO GIVE BAD INFO (TURN L INSTEAD OF R). SUSPECTED COMPASS PROB AND TURNED TO APPROX 180 DEG HEADING FOR 2 1/2 DME AND STARTED L TURN TO 040 DEG. ALSO SUSPECTED BOTH COMPASSES WERE OFF TO SOME DEG? LOCKED IN REAR VIEW MIRROR AT STAND BY COMPASS (COULDN'T INITIALLY DO THIS BECAUSE OF LOW ALTITUDE MANEUVERING AND REALIZED NUMBER 1 COMPASS HAD DRIFTED LEFT APPROX 50 DEG AND NUMBER 2 COMPASS HAD DRIFTED LEFT APPROX 30 DEG. DEP CTL PROVIDED SEVERAL LEFT TURNS AS WE CLIMBED OUT USING BASIC INSTRUMENTS (NO FLT DIRECTORS) AND STANDBY COMPASS. BOTH COMPASSES PROVIDED RELIABLE HEADING INFO WITHIN APPROX 5 MINS. FLT PROCEEDED TO DESTINATION WITHOUT ANY OTHER PROBS. SUGGESTION: AVOID LONG GND DELAYS VICINITY RWY 13 PIER DUE TO STRONG POSSIBILITY COMPASS ANOMALIES. NO ALTITUDES OR SPEEDS WERE BUSTED BUT HEADINGS WERE OFF INITIALLY. THIS TYPE PROB COULD GET YOU INTO TROUBLE VERY QUICKLY IF YOU DON'T REVERT BACK TO BASIC INSTRUMENTS IN A TIMELY MANNER! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: PIC STATED THAT HE HAS KNOWN OF THIS ANOMALY BUT HAD NEVER EXPERIENCED BOTH COMPASSES DEVIATING; ONLY ONE. HAD HE NOT HAD THE FLT DIRECTOR ON HE MAY HAVE TAKEN LONGER TO DETERMINE THAT HE HAD A PROB WITH THE HDG ON DEP. THE SIT WAS CREATED; IN HIS OPINION; BY THE LONG DELAY HE HAD. ATC HAD HIM MOVE FROM TXWY CC AND TAXI AROUND THROUGH BB AND BACK TO CC BEHIND OTHER TFC. TOTAL TIME OF DELAY WAS 25 MINS. AT TKOF ROLL THE COMPASSES APPEARED NORMAL. IN THE PAST WHEN HE NOTED ONE BEING OFF HE RESYNCHRONIZED THE SYSTEM WITH NO DEP PROB. DURING THE INITIAL AND LATER STAGES OF THIS EVENT ATC DID NOT NOTE OR APPEAR TO BE AWARE OF THE PROB. RPTR WAS TO BUSY TO ADVISE DEP CTLR BUT SHOULD HAVE. HE RECOMMENDS: THAT ATC NOT HAVE YOU HOLD NEAR THE PIERS WHEN TAKING A DELAY FOR RWYS 13 OR 22. IF THAT IS UNAVOIDABLE; RESYNCHRONIZE THE SYSTEM PRIOR TO TKOF. THAT: THE NOTE ON THE PRECEDING PARAGRAPH AND PRESENTLY ON THE DEP CHART REGARDING MAGNETIC ANOMALIES BE PLACED ON THE ARPT CHART AS WELL FOR INFO DISSEMINATION PURPOSES. FURTHER: THAT DEP CTLRS BE AWARE THAT DEP TFC OFF RWYS 13 AND 22 MAY EXPERIENCE THIS ANOMALY AND HAVE THEM PREPARED FOR IMMEDIATE VECTORS TO KEEP DEPS ON TRACK.