Narrative:

Midway through our takeoff roll we had erroneous heading information that caused the heading annunciator to come on. We departed from lga runway 13. Runway 13 has a sign that reminds you to prepare for that possibility. We did, however we were cleared for immediate takeoff and as best I could tell had correct headings. The reason for this is that we are not sure if we complied with the noise abatement of lga. After takeoff we turned right to 175 degrees on the first officer's side. His did appear later to be the closer of the two. We had the whitestone climb and at 2.5 mi we then turned to 040 degrees. It was here that we had time to reference the magnetic compass. At that time it showed the first officer's side to be about 10 degrees off and my side to be probably 30 degrees off. Within approximately 10 mins the system corrected itself. This is definitely a problem at lga on runway 13. Maybe it would be a good idea to put some text into our company pages about this happening on runway 13 and that if needed your heading indicators should be manually slaved to the runway heading. Supplemental information from acn 366912: while in position and hold lga runway 13, captain's HSI drifted off approximately 30 degrees and first officer HSI drifted off approximately 10 degrees. Departure was flown off standby compass for approximately 10 mins until both HSI's were aligned again. Believe no significant departure deviations occurred as neither lga tower nor new york departure made any comments. Rest of flight was non eventful. Believe time sitting over pylings at end of runway may have pulled HSI out of alignment.

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Original NASA ASRS Text

Title: AN MD80 EXPERIENCED LARGE HDG ERRORS ON BOTH CAPT'S AND FO'S HSI'S BEFORE AND DURING TKOF AT LGA.

Narrative: MIDWAY THROUGH OUR TKOF ROLL WE HAD ERRONEOUS HDG INFO THAT CAUSED THE HDG ANNUNCIATOR TO COME ON. WE DEPARTED FROM LGA RWY 13. RWY 13 HAS A SIGN THAT REMINDS YOU TO PREPARE FOR THAT POSSIBILITY. WE DID, HOWEVER WE WERE CLRED FOR IMMEDIATE TKOF AND AS BEST I COULD TELL HAD CORRECT HDGS. THE REASON FOR THIS IS THAT WE ARE NOT SURE IF WE COMPLIED WITH THE NOISE ABATEMENT OF LGA. AFTER TKOF WE TURNED R TO 175 DEGS ON THE FO'S SIDE. HIS DID APPEAR LATER TO BE THE CLOSER OF THE TWO. WE HAD THE WHITESTONE CLB AND AT 2.5 MI WE THEN TURNED TO 040 DEGS. IT WAS HERE THAT WE HAD TIME TO REF THE MAGNETIC COMPASS. AT THAT TIME IT SHOWED THE FO'S SIDE TO BE ABOUT 10 DEGS OFF AND MY SIDE TO BE PROBABLY 30 DEGS OFF. WITHIN APPROX 10 MINS THE SYS CORRECTED ITSELF. THIS IS DEFINITELY A PROB AT LGA ON RWY 13. MAYBE IT WOULD BE A GOOD IDEA TO PUT SOME TEXT INTO OUR COMPANY PAGES ABOUT THIS HAPPENING ON RWY 13 AND THAT IF NEEDED YOUR HDG INDICATORS SHOULD BE MANUALLY SLAVED TO THE RWY HDG. SUPPLEMENTAL INFO FROM ACN 366912: WHILE IN POS AND HOLD LGA RWY 13, CAPT'S HSI DRIFTED OFF APPROX 30 DEGS AND FO HSI DRIFTED OFF APPROX 10 DEGS. DEP WAS FLOWN OFF STANDBY COMPASS FOR APPROX 10 MINS UNTIL BOTH HSI'S WERE ALIGNED AGAIN. BELIEVE NO SIGNIFICANT DEP DEVS OCCURRED AS NEITHER LGA TWR NOR NEW YORK DEP MADE ANY COMMENTS. REST OF FLT WAS NON EVENTFUL. BELIEVE TIME SITTING OVER PYLINGS AT END OF RWY MAY HAVE PULLED HSI OUT OF ALIGNMENT.

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.