Small Transport
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Flight Crew Overcame Equipment Problem
Airport
While on Taxiway M; holding short of Rwy 15 at BGR; the compass deviation increased to over 60 degrees; apparently due to a high capacity underground power line. We had HSI1 and HSI2 Caution messages. The Cautions went out when we were cleared to 'line up to wait' on the runway; however the heading was still 089 degrees while lined up on runway 15. As the weather was VFR; we elected to takeoff and continue the flight; navigating via pilotage.Recommend the airport authority provide signs to warn crews of potential compass deviations and avoid holding for any length of time on Taxiway M. Also; add a comment about this phenomenon in the airfield notes.
Small transport aircraft Captain reported experiencing a drastic compass heading deviation allegedly caused by underground power lines on Taxiway M at BGR.