Thanks DowneastGuy. That's exactly what we have had but on appraoch and departure, so low altitude. I was thinking it was a combination of weak field and a bit of interference from transmitters or something which would be stronger near the ground. Your proble is in the cruise so that may discount that theory.
I checked out NuName's idea of the possibiliy of ferrous metal fasteners in the vicinity of the flux detectors with our sparky. That was a 'No'. He did say that if the a/c was struck by lightening that that could magnetise some of the a/c structure and affect the detectors performance, but we ought to know when that has happened and get the compasses swung etc.
Could it be Solar Flares causing this..?
As I have flown an (Collins AHRS) Hawker to 78N and Ivalo 68N without problems, I wonder if the flux detectors in the LJ45 are less sensitive so they require a stronger field to work.
It would be a bit of a worry to lose both nav displays in dep/app with high ground around.
Any more ideas?
D