After I got my PPL, I picked up a portable Garmin GPS to help with navigation and awareness, and it has been wonderful in those respects.

Now that I'm working on my IFR training, it has been repeatedly emphasized that only approved, FIXED installations of GPS can be used for IFR.

I'd like to understand exactly why this is. In my limited VFR experience, I've never seen my portable GPS be inaccurate or otherwise misleading in the slightest.

I can certainly understand the bureaucratic, paper-pusher reasons why they would want to exclude a device that is frequently mounted/unmounted, and may not have a clear view of the sky.

But are there any actual, technically accurate, considerations that make a portable GPS unsafe for IFR flight?

If my GPS has limitations (technical, not legal) that I don't know about, I think I should know about them, even in VFR flight. If this is purely a question of certification/inspection, and not technical short-comings, I'd feel better knowing that as well.

(to state what should be obvious: No, I am NOT asking to use a portable for IFR flight. I'm seeking to understand the practical and legal limitations of my equipment.)

Is the portable RAIM capable? Currency and thoroughness of the database? That might be one reason for the legal stuff.

I'd not use the GPS during your IFR training. It's too easy to become reliant on it. You need to know how to use the certified tools in the plane without using the GPS as a verifier, although it does make life much, much easier.

On another message board, it has been brought up that you can use a VFR gps for IFR flight under the guise of Radar Vectors from ATC. I'm not sure if I agree on that one.

Congrats on the PPL and good luck on the IFR!

Nice article earlier. Read this.

Is It Permissible to Use a VFR-only GPS While Flying IFR? | Flying Magazine | The World?s Most Widely Read Aviation Magazine

Actually you can use a portable GPS during IFR operations, but only for situational awareness, not primary navigation. You have to file based on whatever other nav systems you have onboard, and use those systems for navigation.

The one practical limitation I can can think of is RAIM...portables don't have it. That is a requirement for GPS naviagtion. Also while some portables mount firmly, others just sit on bean-bags on the dash...not very stable in turbulence. Also the power cord might not have a reliable connection to a cigarette lighter plug.

mjarosz: That is an excellent article. Thank you very much. It does concern me a bit that controllers might be giving /U craft direct-to instructions or GPS fixes. I suppose I'm always free to refuse the clearance.

Flying with my instructor one time with my instructor as a /U, we were given a GPS fix. I was prepared to put it into the portable, but the instructor refused. She assumed she had mistakenly filed /G, but I'm sure I saw her file /U and the controller gave us a GPS fix anyway. We opted to cancel and go VFR instead.

The point about RAIM is very good, and probably something to bear in mind.

However, rickair7777 brings up something I think is a point in favor of portables. Most portables run off both batteries and the lighter plug. As far as I know, fixed installations only run off the airplane's electrical system, with no backup. In a total electrical failure, a portable can still run off its internal batteries.

As for the question of database currency, the Garmin 196 gets regular updates that seem to keep it current. (most recently, I saw the KBFI ILS 13R get updated from NOLLA to ISOGE at the same time the new plates came out).

Basically, what I've heard is that, other than RAIM, a portable has all the technical capabilities of an approved installation, its just not approved/authorized.

I'll be finishing my training without any GPS at all (except when practicing GPS-specific flying), and then use my portable for awareness afterward. Based on the article mjarosz provided, I might accept the occasional direct-to in good conditions, but will be purely authorized instruments on departures, approaches, and marginal conditions. Does this sound smart?

Not really. If you do not have any sort of RNAV on board then you should be filed /U. In that case the controller should not offer you direct to anything but a in-range VOR.

Without RAIM there is a very tiny chance that you might get bad data without getting a warning...probably so tiny that you are more likely to get hit by a meteor.

But the real hazard is to your career ...if a fed or ATC supervisor hears a /U aircraft accepting direct to an RNAV fix you might get violated. Private pilots do it all the time...but if they get busted, they will just spend the 30 suspension on the golf course or on the boat instead of flying. The ramifications for a professional are different...

Southwest Airlines was probably the biggest offender of this 15 or 20 years ago. They always just asked for a heading to a fix. There is NOTHING that prevents a controller from using radar monitoring and giving a /U aircraft a heading to any fix. I did it for many years, without incident.

Should the controller just say, "cleared direct Podunk", and you're a /U, a simple reply of, "can you give us a heading for that?" would work wonderfully.

The navigation is the IFR, 100 year old whiskey compass... and ATC radar monitoring with video displayed fixes. Your portable mount GPS is just for situational awareness.

I'm not sure why you're concerned. What do you think might happen? You'll go to your fix (or refuse it, I guess). My suggestion in the above post is to simply ask for a heading (in the enroute center airspace; they have equipment to do this) or offer the heading (military airspace or FAA approach control).

For example:

Bugsmasher 123, SoCal approach, radar contact one mile west of LAX, turn left and proceed direct Sarasota, direct Miami.

That controller either doesn't know you don't have legal stuff (the equipment suffix is NOT displayed on the radar scope) or doesn't care, or just screwed up, because you're "that guy" without GPS/RNAV.

So, respond.... you can make a federal case out of it by refusing the clearance, and blocking the frequency with your pleas of what kind of GPS you have on board (uh... ya, SoCal, ya, uh, like we got this Garbain Mulcher 1000 GPS, and well, uh, ya, uh, we can't LEGALLY go to Sarasota, blah, blah, blah....). Do you think a non-pilot ATC'er knows what kind of GPS is good or bad... or even cares?

Or, you can respond, "left turn, direct SRQ, would a 110 heading work? And when able, then proceed direct to SRQ?"

SoCal: "Yes, BugSmasher 123, that's a smashing good show."

Tony Williams wrote:

Geesh, I wonder why we file, if they don't know & don't care what we file!

The suggestion to always ask for a heading is well taken.

I guess I have to weigh in on this one. As I have said on other boards, I have been asked, IFR, if I have portable GPS on board by ATC. I was filed /U. The controller (Chicago area) asked ME what heading I needed to fly to whatever fix. I told him what it would take, he approved it, I flew it as an assigned heading off airway (legal!!!!). As said previously, it's the RAIM that precludes the use of a portable in IFR.