Narrative:

While waiting for takeoff at laguardia runway 13; we got a dg message and EFIS mis-compare. This area is known for magnetic interference so the message was not unusual. While waiting for takeoff; both left and right side were selected to the dg mode. When cleared onto the runway for position and hold; the dg heading was confirmed to match with the runway heading. Initial heading was climbing turn to 180 degrees until 2.5 lga DME; then left turn 040 degrees up to 5;000 ft. At approximately 500 ft AGL; the both pilots returned from dg mode to the normal mode at about the same time; while still in the initial turn to 180 degrees. Immediately; both compasses spun approximately 30-40 degrees; with conflicting heading information. At that point we were unsure of the correct heading and were approaching the 2.5 DME for the left turn. I started the turn to the left. At that point; ny departure changed our altitude from 5;000 to 3;000 ft. We had already climbed thru that altitude; so we started a descent; still trying to determine the correct heading. We needed to get wings level momentarily to stabilize our magnetos compass. We were given multiple heading changes and a frequency change. Also; we were continuing to troubleshoot the problem by selecting dg mode and returning to normal mode. While all this was happening; the descent was not arrested and descended to 2;600 ft. ATC questioned our altitude. I told them we were having a dg problem and were correcting heading and altitude. The controller asked what heading we were on and I told him we weren't sure. He told us that it looked like we were heading 050. At that point; he had confirmed that we had corrected the problem; had no discrepancies; and continued to white plains to land without incident. The controller was helpful when we told him that we were having a problem. Considering the EFIS mis-compare message had been cleared by utilizing the dg mode; a procedure would be helpful to depart in dg mode. It appeared that when we switched back to normal mode; the situation had not been rectified. It is unclear when the best time to return to normal mode is. Should we have waited? Should we return one side at a time? Wait until level? How long can we continue in dg mode?

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Original NASA ASRS Text

Title: A CL300; affected by a magnetic anomaly at LGA's Runway 13 hold short point; had EFIS MISCOMPARE lights and so took off with the compasses in the DG mode. A track deviation resulted when the heading did not immediately slaved and distracted while troubleshooting the problem; the crew overshot then undershot the assigned altitudes.

Narrative: While waiting for takeoff at LaGuardia Runway 13; we got a DG message and EFIS mis-compare. This area is known for magnetic interference so the message was not unusual. While waiting for takeoff; both left and right side were selected to the DG mode. When cleared onto the runway for position and hold; the DG heading was confirmed to match with the runway heading. Initial heading was climbing turn to 180 degrees until 2.5 LGA DME; then left turn 040 degrees up to 5;000 FT. At approximately 500 FT AGL; the both pilots returned from DG mode to the normal mode at about the same time; while still in the initial turn to 180 degrees. Immediately; both compasses spun approximately 30-40 degrees; with conflicting heading information. At that point we were unsure of the correct heading and were approaching the 2.5 DME for the left turn. I started the turn to the left. At that point; NY Departure changed our altitude from 5;000 to 3;000 FT. We had already climbed thru that altitude; so we started a descent; still trying to determine the correct heading. We needed to get wings level momentarily to stabilize our magnetos compass. We were given multiple heading changes and a frequency change. Also; we were continuing to troubleshoot the problem by selecting DG mode and returning to normal mode. While all this was happening; the descent was not arrested and descended to 2;600 FT. ATC questioned our altitude. I told them we were having a DG problem and were correcting heading and altitude. The controller asked what heading we were on and I told him we weren't sure. He told us that it looked like we were heading 050. At that point; he had confirmed that we had corrected the problem; had no discrepancies; and continued to White Plains to land without incident. The Controller was helpful when we told him that we were having a problem. Considering the EFIS mis-compare message had been cleared by utilizing the DG mode; a procedure would be helpful to depart in DG mode. It appeared that when we switched back to normal mode; the situation had not been rectified. It is unclear when the best time to return to normal mode is. Should we have waited? Should we return one side at a time? Wait until level? How long can we continue in DG mode?

Data retrieved from NASA's ASRS site as of April 2012 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.