Narrative:

On takeoff roll at approximately 120 KTS compass heading annunciator came on, compass split 40 degrees from #1 and #2 as we entered IMC conditions. I was not able to maintain assigned heading because of this situation -- we advised ATC, leveled wings and slaved compass to magnetic compass. This has been a problem in lga, because of the metal piling on which the runway 22 extension is built. Callback conversation with reporter revealed the following information: the reporter stated he was flying an MD88. The MD88 has a glass cockpit but no IRS. Instead, the MD88 has an 'ahars' which is the acronym for automatic heading and attitude reference system and essentially does similar chores to what the inertial reference system does. The reporter stated that though the aircraft with the IRS, like the B767, are not immune to the magnetic interference, the MD88 seems more susceptible than the other aircraft system. The pilots at his airline are made aware of this problem and similar problems at other airports like runway 01 at louisville, ky, and runway 22R at newark. On the MD88 the flight director biases out of view when there is a discrepancy between heading indicators. Being there are only 2, the flight director is unable to determine which is correct. When compass deviations occurred before, the aircraft was stopped on the iron pier and the compass could be reset. In this case the anomaly occurred at 120 KTS. Due to continuous ATC assigned turns the wings could not be leveled long enough to reconcile heading indications from the magnetic compass, which is viewed through a mirror behind the copilot, until about 12000 ft on the climb. There is nothing he would do differently and in absence of correcting the problem he would not change any ATC procedures.

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Original NASA ASRS Text

Title: COMPASS SHIFTS 40 DEGS ON TKOF.

Narrative: ON TKOF ROLL AT APPROX 120 KTS COMPASS HDG ANNUNCIATOR CAME ON, COMPASS SPLIT 40 DEGS FROM #1 AND #2 AS WE ENTERED IMC CONDITIONS. I WAS NOT ABLE TO MAINTAIN ASSIGNED HDG BECAUSE OF THIS SIT -- WE ADVISED ATC, LEVELED WINGS AND SLAVED COMPASS TO MAGNETIC COMPASS. THIS HAS BEEN A PROB IN LGA, BECAUSE OF THE METAL PILING ON WHICH THE RWY 22 EXTENSION IS BUILT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS FLYING AN MD88. THE MD88 HAS A GLASS COCKPIT BUT NO IRS. INSTEAD, THE MD88 HAS AN 'AHARS' WHICH IS THE ACRONYM FOR AUTOMATIC HDG AND ATTITUDE REF SYS AND ESSENTIALLY DOES SIMILAR CHORES TO WHAT THE INERTIAL REF SYS DOES. THE RPTR STATED THAT THOUGH THE ACFT WITH THE IRS, LIKE THE B767, ARE NOT IMMUNE TO THE MAGNETIC INTERFERENCE, THE MD88 SEEMS MORE SUSCEPTIBLE THAN THE OTHER ACFT SYS. THE PLTS AT HIS AIRLINE ARE MADE AWARE OF THIS PROB AND SIMILAR PROBS AT OTHER ARPTS LIKE RWY 01 AT LOUISVILLE, KY, AND RWY 22R AT NEWARK. ON THE MD88 THE FLT DIRECTOR BIASES OUT OF VIEW WHEN THERE IS A DISCREPANCY BTWN HDG INDICATORS. BEING THERE ARE ONLY 2, THE FLT DIRECTOR IS UNABLE TO DETERMINE WHICH IS CORRECT. WHEN COMPASS DEVS OCCURRED BEFORE, THE ACFT WAS STOPPED ON THE IRON PIER AND THE COMPASS COULD BE RESET. IN THIS CASE THE ANOMALY OCCURRED AT 120 KTS. DUE TO CONTINUOUS ATC ASSIGNED TURNS THE WINGS COULD NOT BE LEVELED LONG ENOUGH TO RECONCILE HDG INDICATIONS FROM THE MAGNETIC COMPASS, WHICH IS VIEWED THROUGH A MIRROR BEHIND THE COPLT, UNTIL ABOUT 12000 FT ON THE CLB. THERE IS NOTHING HE WOULD DO DIFFERENTLY AND IN ABSENCE OF CORRECTING THE PROB HE WOULD NOT CHANGE ANY ATC PROCS.

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.