Beechjet 400
Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Other / Unknown
Aircraft Equipment Problem Dissipated; Flight Crew Took Evasive Action; Flight Crew Overcame Equipment Problem
Aircraft; Environment - Non Weather Related
Prior to departure we had discussed the possibility of magnetic compass issues while departing Runway 13 at LGA. We decided to attempt a full length departure and if the problem presented itself we would then ask for a departure from Taxiway AA as recommended on our trip sheet. We were cleared to line up and wait while traffic landed on Runway 22; during this time period I received a red MAG message on both the left PFD and the MFD. The right PFD appeared normal. We advised the Tower that we would need to taxi clear to correct the issue and we were instructed to exit the runway and contact Ground. We did so and the MAG message remained until the left radio master was turned off and back on. We asked Ground if we could depart from Taxiway AA and were told that local policy was not to allow that because of the delay required for intersection departures due to wake turbulence. We decided to try a full length departure one more time. We then taxied back to Runway 13; this time; while taxiing onto the runway; the right PFD displayed the MAG warning followed shortly thereafter by the left PFD and MFD. We advised the Tower we couldn't depart and he said we could taxi further down the runway; off of the bridge portion of the runway; through the 22 intersection. Once clear of the bridge; both displays returned to normal operation. We then departed normally. This is the worst I have ever seen the interference manifest itself at LGA.
A BE-400XP left MAG alerted while holding short of LGA Runway 13 so the crew taxied clear and recycled the left radio master which cleared the alert. When they taxied back to the runway both left and right MAG's alert so they were able to taxi down the runway to clear both before takeoff.