The International Cessna^® 170 Association

I think I get what Robert is saying here. It's a bit outside the "box" given to us by the FAA's basic equipment requirements. Those are based on the traditional method of navigation, which is pilotage (flying a particular heading and airspeed) backed up by a CDI or something else that tells you whether you're drifting off course, so that you can change the heading you're flying as necessary to stay on course. If you're navigating by a CDI, you need a gyro heading indicator.

But a GPS unit is doing all this calculating and correcting for you. It tells you what the desired course is, what track you're currently flying, and how far off course you are. You can stay on course perfectly well using these three numbers off the GPS, without referencing the D.G. (or Heading Indicator, in the current terminology). You can probably maintain course more accurately using the GPS's current track display than you can using a D.G. and CDI.

So Robert's question is, does the FAA yet recognize that an IFR-certified GPS display is enough to keep you on course without reference to a gyro instrument or even a magnetic compass? That's the way most pilots are flying now, after all. Why don't we train pilots the way they're going to fly, and update the regs to reflect common practice?

I guess the answer always is, what's left to rely on when the GPS fails? I fly my 170 with both a panel-mount and a hand-held, so the odds of ever being without GPS are vanishingly small. Without a D.G., if I lost both my GPSs, I'd have to get vectors to VFR conditions and do it by needle&ball and airspeed and whiskey compass -- just like before there was GPS and your vacuum pump failed!

So it seems to me that Robert is making a very valid point, and there's a good argument for changing the required equipment rules for IFR in view of today's WAAS-capable GPS systems. (Before WAAS, I wouldn't have said this. WAAS makes a critical difference.)

John

I guess one answer to my question is, if you don't have a D.G. and ATC says "turn left heading 150," you have difficulty complying with that. You could fly a heading off the compass, check your GPS to see what the resulting ground track is, and then maintain that track. Or you could just fly a 150 track and let ATC correct it to what they want to see, like they always do anyway.

John

Robert Eilers wrote:... The reality is that a IFR certified GPS heading direction display, backing up a wet compass is just as effective and accurate and safe as a Gyro heading direction indicator, backing up a wet compass. .....

NO. It is NOT. And further, any failure of the GPS tracking, such as satellite outage is an example of WHY that's not acceptable as a substitute.

jrenwick wrote: ...But a GPS unit is doing all this calculating and correcting for you. It tells you what the desired course is, what track you're currently flying, and how far off course you are. ...

But it does NOT tell you what your HEADING is. And that is the difference between HEADING and COURSE ...and why a GPS is NOT an authorized replacement for a Gyroscopic direction (heading) indicator.

gahorn wrote:... any failure of the GPS tracking, such as satellite outage is an example of WHY that's not acceptable as a substitute.

I spoke to this in my earlier post. The WAAS-enabled IFR-certified units are a different thing than older panel-mounted IFR-certified GPSs, and FAA regulations recognize this. The FAA considers them reliable enough to be the sole means of navigation (i.e. you don't have to have VOR as a backup in order to use them for instrument approaches).

John

jrenwick wrote:

gahorn wrote:... any failure of the GPS tracking, such as satellite outage is an example of WHY that's not acceptable as a substitute.

I spoke to this in my earlier post. The WAAS-enabled IFR-certified units are a different thing than older panel-mounted IFR-certified GPSs, and FAA regulations recognize this. The FAA considers them reliable enough to be the sole means of navigation (i.e. you don't have to have VOR as a backup in order to use them for instrument approaches).

John

Of course, that has nothing to do with the requirements of 91.205.

gahorn wrote:....But it does NOT tell you what your HEADING is. And that is the difference between HEADING and COURSE ...and why a GPS is NOT an authorized replacement for a Gyroscopic direction (heading) indicator.

Right, but I said this was outside the box. What we're always trying to fly is a line from A to B, and that's a course -- not a heading. If you do this by pilotage, you need a heading indicator. If you've got a device that will tell you what course you're flying, then you can maintain your course using that device alone.

That's an interesting discussion about how to USE a heading (direction) indicator...but it does not pertain to this discussion of required equipment.

Here's the way I fly my 170 now, and I'd love to hear what I'm doing wrong, or how this can be improved. I have a panel-mount WAAS-enabled Garmin 430 as well as a Garmin 496. They are interconnected, so that what ever flight plan the 430 is following is also displayed on the 496 -- including the approach, if one is active. The 430 drives a CDI, in either GPS or VLOC mode. I also have an older King NAV/COM with its own CDI, but I don't use that much.

I enter a flight plan into the 430, either on the FPL page, or simply by entering a direct-to destination. The 430 gives me the course to the next waypoint, which I dial in to the OBS/CDI. At the same time, the pink course line pops up on the 496, and I see my current track on it. The 430 also is displaying my current track and desired track.

Now I use GPS to turn to my desired track -- either the 430 or the 496 will work, and the 496 does it more graphically and intuitively. Hopefully I can get on track before I drift too far off course.

Now, because I learned to navigate almost 40 years ago, I look at my D.G. and start maintaining that heading, watching for any course deviation on the CDI, and correcting with +/-5 degree heading changes on the D.G. Backing up the CDI are the 430's simulated CDI display and the 496's depiction of the course line, compass rose and my position relative to the course. Remember, the goal of navigation is not to maintain an accurate heading -- it is to track a course from one point to another.

I have two completely independent systems backing up my FAA-required panel that I use for primary reference, and any one of them would keep me on course just as well -- unless the GPS system external to my aircraft failed in some catastrophic way. With the redundancy provided by WAAS, this is far less likely than a vacuum system failure on any given aircraft.

So, regardless of what is legal today (and I'm not doing anything illegal), given the current state of the art installed in a 55-year-old airplane, why shouldn't the FAA revise the minimum equipment requirements to permit IFR operations without a directional gyro?

I think that's the question behind what started this thread, and it's a very good one. IMHO.

John

It is a very good question and there is a simple answer. These navigation devices are built to technical standard orders as are other instruments installed in certified aircraft. The manufacturer of the equipment must apply to the FAA for approval to use these devices for those specific purposes. There is a TSO for IFR GPS and I believe there are TSOs for directional gyros (any sparkys out there?). As I mentioned earlier, contact the manufacturer (Garmin) and ask them if this is an appropriate use of their equipment and if they have recieved FAA approval for that use. The FAA does not have their head in the sand. It is entirely up to the manufacturer to determine what use their equipment is intended for and get FAA approval. FSDOs have absolutely nothing to do with this subject, by the way, other than to follow guidance in flight manual supplements just as pilots are expected to do. In order to ensure safety, pilots must read flight manual supplements for this type of equipment and make sure they operate within those limitations. The descriptions by Jrenwick and Robert E. suggests that the equipment is capable of meeting these requirements, so contact Garmin and see if they agree. Then Garmin can contact the FAA and get approval if their data meets certification requirements. This may actually be a good idea/suggestion so someone should follow up on it. Try contacting Garmin Customer service and see if there is they have someone in engineering that will discuss this. The description by Jrenwick is also an excellent example of single pilot resource management and represents a safe and very legal way to operate a single engine airplane under IFR. As for me, I really enjoy flying VFR and hope I do not have to deal with issues like this.

jrenwick wrote:...So, regardless of what is legal today (and I'm not doing anything illegal), given the current state of the art installed in a 55-year-old airplane, why shouldn't the FAA revise the minimum equipment requirements to permit IFR operations without a directional gyro?...John

As Voorhees points out, ...if you feel strongly about this.... you can attempt to have the rule changed. But I predict a fruitless effort, and suggest that the reason the rule has not been changed is because the GPS ...(it's "compass rose", you inadvertently and erroneously referred to).. is actually NOT a compass at all. It's a "tracking" depiction, not a "heading" depiction.

Suppose you are flying in a 50 kt. headwind (strong winds at altitude, for example)...and ATC asks you to fly a particular heading to avoid traffic....and the ONLY thing you had to rely upon was that Garmin GPS? You can see that ATC might become a little upset when your track is very different than what they intended with regard to other aircraft in the area.

As far as the thread question the current FARs require a gyroscopic driven DG. Pretty clear here.

As far as a discussion of whether a gyroscopic driven DG is required in practice. No it is not. You can use a GPS to turn to a heading when given by ATC just as accurately as a DG. Remember a DG is only as accurate as the last adjustment to heading. What was used for that adjustment? A whiskey compass swinging left and right of heading 15 degrees? Now that's accurate. Then add in a little precession in there to boot.

When ATC gives you a heading they are trying set or change your course. Most times giving a heading works well enough and when it doesn't a correction is given.

The failure of a GPS system as an argument to have a gyroscopic driven DG doesn't hold water as the whisky compass is the backup for either when a better instrument is not available. When given a heading while flying my Cub I use the whiskey compass which in most cases is all the directional equipment I have on board.

I believe the FAA is slow to change in most cases. Sometimes that works in our favor sometimes it doesn't. I think the resistance to GPS and its capabilities and reliability is one of those cases that it is not working in our favor. And I'm not talking about throwing caution to the wind here.

I predict that 20 years from now, when most pilots and FAA have grown up learning and flying the G1000 systems and others to come, that the current antiquated regulations will be changed. And there won't be any George's, Robert's, John's, Harlow's and Bruce's of yesteryear to argue.

In most daily flights yes...the gps is all the precision needed. But a 45-degree heading change made in a 50 kt wind will not result in a 45 degree track change. Nor will a 10-degree heading change on an ILS in a strong crosswind likely result in a ten-degree track change. For those reasons I don't agree that a gps will replace a good compass, regardless of whether it's gyro-driven or not, and a DG that precesses so excessively as you describe Bruce is not an airworthy instrument. Just because an unairworthy DG is unreliable isn't a valid argument for replacing it with gps.

"Lindbergh found Paris within ten minutes of when he predicted ...with a compass and a clock."

N9149A wrote:...........I predict that 20 years from now, when most pilots and FAA have grown up learning and flying the G1000 systems and others to come, that the current antiquated regulations will be changed. And there won't be any George's, Robert's, John's, Harlow's and Bruce's of yesteryear to argue.

What a pity that will be, debate is healthy and educational. Although, given the current state of our County, we may already be there. It seems we have been reduced to shouting epithets at each other and are not bothering to try and see the Forest for the Trees.

gahorn wrote:....Suppose you are flying in a 50 kt. headwind (strong winds at altitude, for example)...and ATC asks you to fly a particular heading to avoid traffic....and the ONLY thing you had to rely upon was that Garmin GPS? You can see that ATC might become a little upset when your track is very different than what they intended with regard to other aircraft in the area.

I mentioned this problem in an earlier post, where I said that without a D.G. you'd have to turn to the heading using the magnetic compass, then maintain the resulting GPS track. If the compass-based turn is off a little bit, ATC will correct you, as they always do.

For that matter, I assume ATC knows I'm GPS-equipped, because I said so on my flight plan (aircraft type C170/G). If they took advantage of that and vectored me using ground track directions instead of headings, they'd probably have to issue fewer corrections to get what they want to see. The number of so-equipped aircraft in the IFR system must be growing, and at some point the aircraft that couldn't accept a "track vector" will be the exception to the rule.

John