Narrative:

Our clearance out of lga required a turn to a heading of 360 degrees after takeoff on runway 31. Our gate is very close to the departure end of runway 31. Start up, checklists, and taxi involved less than 4 mins and we were cleared for takeoff upon reaching the end of the departure runway. During the takeoff roll I noted that my HSI read 350 degree when it should be reading 310 degrees (runway heading). The captain's HSI and both our RMI's read the same erroneous heading. No flags or instrument failure warnings were present. With some help from departure control, we managed to get on our correct heading and subsequently re-synced the HSI's against the wet compass. All further operations were normal but we may have set off some noise monitors due to our initial confusion about our heading. We learned later that the gate we had parked at prior to our departure from lga had produced gross compass swings in the past on some aircraft. Evidently some magnetic anomaly is present there, producing as much as 40 degrees of compass swing. A subsequent rapid departure does not give the compass system time to re-sync to correct heading and if the crew doesn't catch it (we didn't) a problem after departure can develop. Our company has since issued a NOTAM in our release papers that warns against compass swing possibility at that particular gate.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB CAUSED BY ARPT PROB RAMP STANDARDS.

Narrative: OUR CLRNC OUT OF LGA REQUIRED A TURN TO A HDG OF 360 DEGS AFTER TKOF ON RWY 31. OUR GATE IS VERY CLOSE TO THE DEP END OF RWY 31. START UP, CHKLISTS, AND TAXI INVOLVED LESS THAN 4 MINS AND WE WERE CLRED FOR TKOF UPON REACHING THE END OF THE DEP RWY. DURING THE TKOF ROLL I NOTED THAT MY HSI READ 350 DEG WHEN IT SHOULD BE READING 310 DEGS (RWY HDG). THE CAPT'S HSI AND BOTH OUR RMI'S READ THE SAME ERRONEOUS HDG. NO FLAGS OR INST FAILURE WARNINGS WERE PRESENT. WITH SOME HELP FROM DEP CTL, WE MANAGED TO GET ON OUR CORRECT HDG AND SUBSEQUENTLY RE-SYNCED THE HSI'S AGAINST THE WET COMPASS. ALL FURTHER OPS WERE NORMAL BUT WE MAY HAVE SET OFF SOME NOISE MONITORS DUE TO OUR INITIAL CONFUSION ABOUT OUR HDG. WE LEARNED LATER THAT THE GATE WE HAD PARKED AT PRIOR TO OUR DEP FROM LGA HAD PRODUCED GROSS COMPASS SWINGS IN THE PAST ON SOME ACFT. EVIDENTLY SOME MAGNETIC ANOMALY IS PRESENT THERE, PRODUCING AS MUCH AS 40 DEGS OF COMPASS SWING. A SUBSEQUENT RAPID DEP DOES NOT GIVE THE COMPASS SYS TIME TO RE-SYNC TO CORRECT HDG AND IF THE CREW DOESN'T CATCH IT (WE DIDN'T) A PROB AFTER DEP CAN DEVELOP. OUR COMPANY HAS SINCE ISSUED A NOTAM IN OUR RELEASE PAPERS THAT WARNS AGAINST COMPASS SWING POSSIBILITY AT THAT PARTICULAR GATE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.