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Something came up yesterday between my CFII and myself during an IFR approach, so let me describe the situation and I welcome thoughts and opinions.

The Setup: We were outside the initial approach fix to VOR/DME Rwy 27 at PDK (Atlanta), but already established on the approach and the OBS needle was centered. Mid-afternoon thermals were kicking us around pretty good at 3000'. My cantankerous CFI chose this moment to pull out her gauge covers and put me into partial-panel. However, I have a panel-mount GPS unit that is IFR certified, which at this point I was using for DME to the VOR. Of course, this unit also shows ground speed and ground track.

As the approach continued we were getting pushed to the left so I corrected to the right. But the chop was so bad that the compass was getting bounced incessantly and made it difficult to get a reading. So instead I got the OBS needle recentered and then kept it there by maintaining about 280 degree ground track (approach course is 277). I figured as long as the needle is centered and I stay on a ground track that matches the approach course, I should be pretty good.

Then I heard her exclaim "You've way over corrected! Your compass is showing 330, that's a 50 degree correction!" She calmed down a bit when she realized that this was the result of turbulence jostling, but it began a discussion between us about the difference between compass heading and ground track.

I've been using GPS since the early 90s (for backcountry stuff) and like VOR, I know that GPS doesn't care one whit which direction your aircraft is pointed...it shows the actual path across the ground. I'm not sure I convinced her of this, though.

In the end, my question to the group is this. It would seem to me that in a vacuum failure (real or simulated) using any valid technology at your disposal to ensure a safe outcome is legit. And with turbulence kicking the compass around, the GPS ground track showing steady progress along the desired compass heading is a valid way to maintain direction. But would this be considered acceptable to an FAA examiner? More importantly, based on your experience, would this be an effective way to manage an approach in a real situation?

Thanks in advance for your input.

Jeff

Jeff,

Excellent point, and I would agree that your technique has merit and is valid for use. However, as you stated, it’s a question of whether or not an examiner would accept this method. This may depend on the examiner, and I’ve noticed that some of the old school examiners seem to have the mentality of, ‘I learned it this way, and so should everyone else’. They appear reluctant to change and resist the benefits of modern technology for reasons that don’t convince me.

Not to long ago I had a similar situation with a student. As my student was performing a series of compass and timed turns, he reach over to the Garmin-430 and turned it to the page that shows the electronic version of the compass card, representing the aircraft’s ground track. He then asked me why he simply couldn’t use this instead of struggling with compass turns?

To be honest, I really didn’t have a good answer for him, other than to say that it’s a skill required by PTS. His point was definitely valid, since compass turns are assuming either a DG or a vacuum system failure, not an electrical failure which may or may not rob you of your GPS heading data.

Let’s keep in mind that PTS is a government document, and the government is often slow to change or keep up with the times. The PTS was written back before the days of modern GPS and glass cockpits, so it reflects practicing for a worse case scenario, and we can’t always assume everyone has access to modern day GPS or glass cockpits. But I do agree that the document could be revised to reflect these changes if our aircraft are equipped and so capable. Because after all, what could be more fun than a partial panel NDB approach?

I share your sediments,
Ken
PDK CFII