IFR approaches with true headings

[Mouthoftireddog]

Hi all, long time reader, first time poster.

I have a few questions that I haven't been able to dig up any information on. It concerns IFR approaches in northern Canada using true headings, tracks and radials on approach plates. I understand the relationship between true and magnetic headings in relation to variation, but I'm still unsure how a pilot would go about actually flying this type of approach and not flying astray.

I've found some plates for YRT on google to help direct my questions
http://www.ivao.ca/charts/CAP1//CYRT.pdf

Questions:
1. For example, you are trying to fly the RNAV RWY31T into YRT via OVESA. Obviously you are tracking direct OVESA with your GPS, but once you hit it and need to turn 039T. Assuming your in a IFR certified plane with a GPS slaved to your HSI/RMI, the next heading with be 039T. This is where my questions come from. Most of the 703,4,5 stuff flying around have slaved compasses. There seems to be 0 variation at YRT, so is it safe to assume that magnetic heading (what is read off the HSI/RMI) will be equal to the true heading as depicted on the plate?

2. How would an approach be flown at an airport using true headings with significant variation when your magnetic slaved compass is pointing to the magnetic heading. Would you simply unslave it prior to the approach, correct it using the variation on the approach plate and fly the approach like that?

3. Looking at the VOR 13T in YRT, assuming you wanted to hit the VOR and track the 301T radial to the arc, would you just intercept and fly the slaved HSI 301 radial (assuming true = magnetic)? If there were more variation, would you unslave everything, correct the system with the variation and fly it that way?


I realize these are some time consuming questions, but this has been bothering me for a while. I would really appreciate some insight to this. I've never flown in the arctic.

[ahramin]

As soon as you have crossed the line into Northern Domestic Airspace, you take your HSI off slave mode, put it into free mode, and set it to True North. As you fly you periodically set it to correct for precession and convergence, especially before starting an approach. You fly the approach just like you would down south.

[oldncold]

Ahram is correct! Another helpful thing is; some but not all airports have the variation in the cfs or on the plate for the aerodrome chart. Gps is generally very good until 70' latitude after that it can get spotty . If your aircraft doesnt have slave mode or IF AND ONLY IF your have the published variation on current cap chart one might use the mag heading corrected for the variation to true heading .

Take a current cap chart and write in the corrected headings for the procedure. DO THIS ON THE GROUND well before departure . the gps will usually get you there at high alt as it picks up more southern satellites and ndb's are good ole school back up. Brief the procedure thoroughly! Something like this //this will be the ndb freeze ones ... off nunavut plate is effective sept 2012 elevation 250ft. we will apply cold corrections today for temp of -42c to all procedure alt . comms set. nav tuned tested set identified ... initial heading to the approach fix 045 t magnetic heading 003' etc be safe and dont forget the snow goose and baffin boots

[ettw]

With respect to correcting CAP approaches from true to mag, I don't think thats legal.

With respect to GPS ops north of 70, I have not had any problem darn near to the pole. Convergence of course fouls up the GPS closer to 90N but I am not aware of any IFR approaches north of CYLT.

In my experience, the "normal" DGs ie. KG102 etc do not run well in free. Precession will be a bitch to keep up with. Our ops are with C11 gyros which were designed to run in free with an internal precession of about 1.5 deg/hr. Not bad. Of course with the IRS or APIRS that are now installed in new equip, I would expect precession is a thing of the past.

If you slave your HSI system to the GPS you will have only track info, not heading info displayed. That might be a problem if you have a howling xwind on approach.

Basically IFR ops in Northern Domestic Airspace is just like Southern Domestic, just a different N reference. VORs are oriented on True North which, if you were to operate in mag in NDA, could mess with your situational awareness. See CYCB VOR approaches.

As well, the CAP does not give the variation of airports in NDA. It was removed earlier this year.

Cheers.

ETTW

[ahramin]

I would not be using a magnetic DG corrected for variation in NDA. There's a reason everything is in true: compass indications are not reliable close to the magnetic north pole.

The proper tools and procedures are available. It's just a matter of getting them and using them.

[ettw]

With respect to using mag headings in NDA, there is really no issue other than legalities, at least south of 70N or so.

There was a time (mid 90s) when the mag pole was within Canada. Now it's off the coast of Axel Heiberg island by a few hundred miles or so and practically speaking mag could be used with. O issues.

In fact there was an operator in the Arctic who ran in mag all the time with no problems. It's just not legal and as was pointed out, the technology is there to operate legally within NDA.

ETTW

[Mitch67]

I myself am a bit confused after reading the responses to the questions posed.

One enters into northern domestic airspace enroute to an airport requiring true headings for the approach. You take your slaved HSI off it's slaved mode, and let it free. You correct its last "slaved" magnetic heading for variation found on the LO/HI chart. Therefor the compass will now read true north and not magnetic north taking into consideration the precession errors requiring your to reslave the compass, and correct it every now and then. All the while you are tracking using VOR/NDB/GPS to cross check position too?

One thing I found interesting is the removal of variation from approach plates. In this case, do you just look at your Lo chart for the variation prior to commencing the approach, correct the HSI to ensure accuracy and fly the unslaved HSI?

[trey kule]

I must be missing something here. You use true tracks, headings in the NDA. Variation has nothing to do with it? It is why the charts are based on true tracks. It is why you are taught at the ppl stage about the vagracies of the magnetic compass, and why we have he hold region set up. So why are you people posting about mag variation and corrections in the NDA. Why ,oh why are you even considering correcting from the published true headings to a magnetic heading?

Interesting briefing old and cold. Kind of resembles one from an FTU, rather than an actual operational one, but perhaps it is one your mop any uses

[ahramin]

Mitch67 you seem a little mixed up with the whole idea.

Once you cross into NDA your HSI is in free, you no longer set it to anything magnetic so no need to correct for variation. That's the whole point. You should have a good idea of how much your HSI precesses per hour, which you will adjust for. You will also calculate the convergence due to how far east or west you have travelled, which you set. Lastly, you can check your true heading with an astro compass, or a GPS and ADF bearing.

You don't use GPS or VOR to cross check position, you use it to navigate.

[Duncan Idaho]

Yeah there's no variation calculation required. In fact it wouldn't even be very possible to try to figure out what your true heading is by any compass reference because the compass only really works in the aircraft I've taken up there with your generators, windshield heat etc OFF and the compass swings are conducted that way.

You're basically only referencing the tracks you read off your GPS or VOR. Though I doubt anyone ever uses the VOR because the GPS is so much easier to use and more precise. To be honest with you when I cross into the NDA I set my HSI to free mode, and turn it to whatever I'm tracking on the GPS. I have an idea of where the wind is coming from so I'll point it a few degrees that way. Then when you're on a runway at your next airport, you will set the DG to the published runway heading and fly off using that.

In reality though no one is doing an approach by taking the heading and watching for drift then applying incremental corrections. You turn inbound at the IAWP then match up the DTK (approach track) with your TK (what you're tracking) and keep them there. The DG's heading is just for spatial orientation and an emergency backup IMO, it's not really required with any sort of IFR GPS and flying a heading off the DG would just hinder your precision. Fly the track on the GPS.

[ettw]

Mitch67, here's how we operate in NDA.

Leaving SDA into NDA when departing say YFB, we switch the compass system to DG or FREE. We switch the GPS to True. We then drive our compass heading to read our true heading. The true heading can be determined either by applying variation (and thats the last time I'll use the term), or using the GPS, we obtain the current bearing to the nearest NDB. We then drive our compass heading until we see the bearing to the NDB dispayed on the RMI. We are now operating in TRUE.

All of our navigation is done in true. Regardless of what type of track we're using (VOR, ADF, or 99.98% of the time, GPS direct. The compass will display true heading info and the GPS will display true bearings or tracks.

Along the we we will verify the accuracy of our heading info. This can be done either with another ADF bearing as per the original setup or using the astrocompass. Yes we still use that. Ask any of my FOs and they'll tell you I'm a tyrant with respect to knowledge of that piece of equipment.

In fact you don't need the astrocompass. I have pitched the shadows across the cockpit or from the windshield post towards the cockpit bulkhead to get a sunshot as well.

At the top of decent, we once again verify the heading info, generally using an ADF bearing. Depending on the level of service our DG is giving us, we might only have to apply convergence but usually, even our C11s will precess slightly and the ADF bearing corrects all of that.

The approach is flown just like in SDA.

On departure out of an airport in NDA we will set up the compass on the taxi based on the published info in the CAP or the displayed ruway heading info as you taxi to the runway. If we are offstrip, we just take a glance at our GPS which will display our track as we taxi.

Thats it. And I only used the word variation once.

Cheers,

ETTW

[rapid602]

Never been north of Fort Severin in Ontario. Have never in NDA. It was interesting reading your posts.

Thanks guys fly safe !!!