Partial Panel + VFR GPS

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In a recent article exploring the use of an IFR-approved GPS, Jeremy Jankowski briefly explained how to use the GPS during a partial-panel situation. In a follow-on to that article, John Ruley goes more deeply into the partial-panel situation, and poses the tricky question: Can you use a VFR-only GPS in a partial-panel situation?

Recently, I flew a practice ILS approach, hooded, and partial panel (with the AI and DG covered up). It was surprisingly easy — much easier than usual — because I used my VFR GPS to substitute for the DG, and to assist with keeping on the localizer during the ILS final approach.

Here are the questions: (1) Is this legal; and (2) Is it a good idea?

Partial-Panel Practice

To explain: I've been spending a little hood time lately to maintain my instrument currency (my next Mexico trip is in just over a week, and I need to be instrument current for it). I asked my wife Kate (a private pilot) if she'd like to be my safety pilot, and headed for the airport.

I was also uncomfortably aware that my last partial-panel work was during my BFR, which was last year. I do practice partial panel in Microsoft Flight Simulator (more on this below), but rarely do so in the airplane. So I decided to throw myself a curve and do the approach partial panel.

  Intercepting the Stockton  ILS Rwy 29

My hood-work routine is to take off visually, do a left-crosswind departure, and put the hood on as soon as I'm stabilized in climb (telling the safety pilot, "The outside world is up to you," as I do so). Then I fly to SHELI intersection, which is about 7 miles from Modesto — just outside the Class D controlled airspace. I go into a hold there (which takes care of the requirement to practice holds), and call Stockton approach for my practice clearance.

I did that as usual, but covered the AI and DG while making the first turn after passing the intersection. Boy, was I ever rusty on partial panel! It took several tries before I remembered how to fold paper from my clearance pad so that it would fit inside the instrument bezels and cover the gyros. While doing that, I flew well past my planned heading and lost about 400 feet. N5142L has both a vertical-card magnetic compass and the usual compass on the windscreen; I started my turn back, staring at the vertical-card compass, while climbing — having momentarily forgotten about magnetic compass errors ...

... If you haven't flown partial panel for awhile, the first few minutes can be a scramble. Trying to do a hold at the same time is a real challenge!

Ah-Ha! — The GPS!

At this point, I remembered about counting (three degrees per second at standard rate) to roll out at an assigned heading. I was just about to do that, when I realized that I had another option — my Garmin 195 GPS — on a yoke mount right in front of me. One of its displays includes a simulated DG. Of course, it's based on your ground track, but that's not drastically different from your magnetic heading. It worked beautifully! There is a lag, but you can deal with that easily by shallowing the turn as you approach your target heading. When I rolled out, I crosschecked it with both magnetic compasses to make sure I wasn't being misled, and from that point on things got a lot easier. Once I got stabilized, I was able to hold heading and altitude well within IFR practical-test-standard limits (and this on a bumpy day, with lots of scattered cumulus!)

Next, I called Stockton and got clearance for a practice ILS. It was a fair amount of work to maintain a constant heading — but much easier using the GPS as a heading reference. When I captured the localizer, I switched to the GPS's simulated CDI. It matched the localizer (I cross-checked regularly from this point on), but also gave me an arrow indicating my track — not quite an HSI, but close. With that, holding the localizer was almost as easy as it is when flying the ILS with full panel!

I rode it all the way down to minimums, and when I popped off the hood, I was looking right at the end of the runway. Kate said I was weaving a bit (I was turning back in towards the glideslope whenever either the GPS or localizer indicated any motion away), but was under control the whole way down. That's a lot better than I would have been able to do it using conventional partial-panel techniques.

Yes, But Is It Legal?


We landed, and taxiied in, and Kate said, "So, is that cheating?" I said "Yeah — but as far as I'm concerned, partial panel is an emergency, and if it happens for real, I'll use whatever tools I've got!" Then I got to wondering ...

AIM 1-1-21 e.1.(a) sounds pretty unambiguous:

"Visual flight rules (VFR) and hand-held GPS systems are not authorized for IFR navigation, instrument approaches, or as a principal instrument flight reference."

But the very same paragraph concludes:

"During IFR operations they may be considered only an aid to situational awareness."

That's generally interpreted to mean that it's OK to look at the moving map — but you have to have your other instruments tuned, and you use them for navigation, referring to the GPS only for a general idea of your location. Clearly, I was doing more than that — but not by all that much. My IFR navigation was being done first through vectors from Stockton, and then using the ILS. My primary flight references were the turn coordinator, airspeed indicator, and magnetic compass — I simply used the GPS as an aid to know my actual heading during turns, when the errors inherent in a magnetic compass make that all but impossible.

I ran my procedure past a number of experienced pilots — including two CFIIs — and got mixed reactions. One complemented my "use of everything available to you." On the other hand, another said, "When I did hooded partials, there was no such thing, and I was a better pilot for it ... backup instruments aren't a guarantee."

I still think my initial answer to Kate was a good one: For me, partial-panel under actual IMC is a real emergency, and I intend to treat it as such. Once you declare an emergency, you're permitted to use whatever means you need to save yourself and your passengers.

Declaring an emergency to ATC should eliminate the need to do something as complex as a partial-panel hold (particularly right after the gyros fail). The first thing that's called for is a period of straight-and-level flight to get things trimmed and get as comfortable as possible flying the airplane on partial panel. Then get vectors, preferably to VMC, or at least to an airport above alternate minimums (you have to declare one when you file IFR, after all!)

Future Training

  Instrument Panel

But this experience convinced me to go one step further: I'm going to make the GPS a regular part of my partial-panel training. An actual emergency isn't the time to figure out how to work it into my scan!

With that said, I also plan to practice partial panel more often — both using the GPS and with it turned off. There's always a risk that a gyro failure might coincide with an alternator malfunction and a dead battery in the GPS — or, just as dangerous — a malfunction that renders the GPS useless. And believe me, this isn't just theoretical: In the last four years, I've personally experienced one full vacuum failure, an AI failure, and multiple electrical failures (which finally required a new alternator). The GPS hasn't failed me yet, but that's only a matter of time. (If I'm doing partial-panel and see a large difference between the GPS track and compass heading while wings-level, it's time to turn the GPS off!)

A GPS can also be a lifesaver during a pitot-static failure. (I've even had one of those — fortunately in VFR conditions — after neglecting to cover the pitot tube when washing my airplane.) You can use the GPS ground speed as a substitute for airspeed, and the GPS altitude instead of the barometric altitude.

Flight Simulator Training

If you have Microsoft Flight Simulator 2000 or 2002, you can practice vacuum, pitot-static, and electrical failures: Select System Failures from the Aircraft menu. Check the "arm" box for the system(s) you want to fail, and enter a time range. To make things challenging, select Weather from the World menu , set overcast clouds, and visibility of one mile. Then take off — but be prepared for things to fail, and don't assume they'll be instantly obvious. Just as in a real vacuum failure, Flight Sim's AI will slowly roll over and die, while the DG stops moving.

To see how effective a GPS can be in this situation, select View/Instrument: GPS. Flight Sim's GPS is more sophisticated than most actual hand-helds; but it will definitely give you the idea. Simply using the moving map gives you a visual reference for heading deviations, and the GPS heading doesn't suffer from the leads and lags in a magnetic compass (which Flight Sim also models accurately).

Then, try it in your airplane — because there's no substitute for actual hood work!