High Latitude Flux Detector Problems

[Dumbledor]

We have had problems with AHRS Hdg Fail on both sides on LJ45 at Ivalo 6837N, Tromso 6941N & Evenes 6829N at low altitude (Approach or initial climb).

I've flown to Rovaniemi 6634N in a LJ35, Svalbard 7815N and Ivalo 6837N in a Hawker 800 (not IRS) without similar problems.

I realise that with Magnetic dip being greater in these places the horizontal component of the field, that a compass or flux detector needs to work, is relatively weak. I was wondering if this is more of a problem for the LJ45 and if any of you have experienced the same problems. I am wondering if the weak horizontal component of the field could be affected more by local radio-magnetic interference while at low altitude..

Lucky pilots with IRS will not have this problem as they use true north..I wish!

Thanks in advance.

D

[NuName]

You may just want to check that someone has not replaced any fasteners in the vacinity of the flux detector with ferrous metal components, unlikely but has been known and will cause the problem.

[Paradise Lost]

....was how I first read the thread! A sort of fartometer I supposed? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/eek.gif

[Dumbledor]

Thanks NuName, I will check it out.

As for PL, come to think of it I wouldn't like to have to read the heading after a few! :}

Cheers

D

[DowneastGuy]

We're having the same problem on an occasional basis with our 45. AHRS Heading Fail on the left side followed in 5 - 10 seconds by a failure on the right side, usually in cruise. It usually resets with a cycling of the compass switch to free and back to slave.

What's disconcerting is that you lose all nav displays on both sides and the checklist doesn't mention this. The Bombardier FSR has been checking into the problem on our aircraft and said that other aircraft are having the same problem.

[Dumbledor]

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

[Dumbledor]

I have recently learned that Bombardier do a mod to the flux detectors for LJ45's operating in these latitudes. but for how much? The chances are the company wouldn't pay for them anyway unless we went there often enough so we will have to carry on with the standard inferior kit.

It sounds like the older collins flux detector/AHRS may have been better. Any truth in that?

We need IRS to completey solve this problem and provide immunity from magnetic storms as they align to True North. The solar flare activity in 2012 is expected to be powerful enough to knock out power grids, so our little compasses may have a few problems as well.

D

[eckhard]

I was in Ivalo last Feb in a CJ1+ (mag flux detectors and AHRS) without any problems. In a CJ1 (same compass system) at Tallinn, we experienced HDG anomalies on the ramp, but they cleared as we taxied out and cycled the system from AUTO to DG and back. We put it down to electrical equipment on the ramp, which was later confirmed by the handling agent.

[Bruce Waddington]

D,

This is a known problem on the Lear 45.

The most likely causes of the HDG FAIL message are: local magnetic disturbance, low magnetic field strength, or AHRS fault or failure.

We had the Captain's HDG FAIL come on just north of Thunder Bay (YQT), Canada, while at cruise altitude. Apparently there is a low magnetic field strength problem there.

best regards,

Bruce Waddington

[Dumbledor]

Thanks Eckhard and Bruce.

We get the HDG comparitor issue on the ground a lot with the '45, but more than on other types that I've flown even though this is to do with metal or cable under the concrete. It was interesting to hear that the CJ1 didn't have any problem at Ivalo. Is that a Honeywell fit like on the '45?

By the way we had HDG fail problems at Evenes, Norway (69N) a few weeks ago in the climb-out also.

The fact that Bombardier do a mod for A/C operating at higher latitudes does imply that the '45 flux detector/ AHRS doesn't work as well as it could, at least compared with other a/c.

D