IFR Certified GPS

Jaybird180

Jaybird180

Final Approach
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Jaybird180
Reading another thread, there was discussion about substituting GPS (only in certain cases) for DME or ADF. What I don't understand is why are there restrictions on using GPS to identify where you are in 3 dimensional space, what additional capabilities does having a "certified" GPS give the pilot and why are there ANY restrictions on using GPS in lieu of other equipment (twist on the first question).

Someone please explain.
 
Certified means built to a standard (TSO) the FAA found acceptable AND installed in an FAA approved way, sticking a TSOed for enroute and approach capabilities in your panel won't let you "legally" fly any IFR with it, you need annunciators, installed in the correct place and CDI's installed in the correct space, antenna has to be in the right place AND you have to draw up a document, AFM Supplement, specific for your installation that describes the systems in your plane and how they interact with each other. All this has to be signed off by the FAA.. DAMHIK
 
Okay so the unit must be part of a certified "system" to be considered legal. I think I got it.

BTW- the answers to my other questions were referencing Ch 7 of the IFH, which is exactly where I am in my reading. So eventually, I'll get my answers.
 
Jaybird180 said:
Okay so the unit must be part of a certified "system" to be considered legal. I think I got it.
Click to expand...
Just to be clear - no handheld/portable GPS regardless how fancy is certfied.
Many old GPS certified aviation receivers (still installed in many airplanes) were only certified for the enroute flight, no approaches.
 
Jaybird180 said:
Okay so the unit must be part of a certified "system" to be considered legal. I think I got it.

BTW- the answers to my other questions were referencing Ch 7 of the IFH, which is exactly where I am in my reading. So eventually, I'll get my answers.
Click to expand...


For VFR, I think the IA/Avionics shop can just shove a GPS in the panel and sign it off for VFR, if you want to use it for IFR, you have to work with the FAA to get their blessing, do flight tests etc... i.e. more time, parts, paperwork and most of all ... money. There's a fairly new AC out on IFR GPS installs, I had about a half hour talk with the local FSDO and that's my understanding, I'm no expert on this. I just had an IFR GPS installed for IFR, was about a 7 month ordeal to get all the ink dry, I think I had a worse experience than most would.
 
I can't vouch for your ordeal, but an IFR GPS installation is not that involved. You buy the unit and the STC. Install it and test according to the installation instructions, file the 337's and then it's VFR only until you do one approach on it. Then you sign that off and send the package over to the FSDO.
 
flyingron said:
I can't vouch for your ordeal, but an IFR GPS installation is not that involved. You buy the unit and the STC. Install it and test according to the installation instructions, file the 337's and then it's VFR only until you do one approach on it. Then you sign that off and send the package over to the FSDO.
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I don't have an STC that I'm aware of. There's a new-ish AC out and I believe it requires 3 approaches now too. This project started March/April, 337s went in the mail on Tuesday.
 
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bartmc said:
I don't have an STC that I'm aware of. There's a new-ish AC out and I believe it requires 3 approaches now too. This project started March/April, 337s went in the mail on Tuesday.
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What GPS are you installing and what aircraft? I put a GNS480 in a Navion
(not the most popular combination out there either).
 
Think of it like the stupid panel mounted clock requirement.....bureaucracy is a biotch.

Just like handheld timers, there are alot of much better reliable and capable handheld GPS units compared to some of the older panel mounted certified ones.
 
flyingron said:
What GPS are you installing and what aircraft? I put a GNS480 in a Navion
(not the most popular combination out there either).
Click to expand...

KLN89B in a PA28 150, I can find no STC (not in my paperwork or on the FAA website).
The AFM supplement was based off a B/K one but had to be tailored to my aircraft and N-Number specific. We also had to get the FAA to approve where the annunciator was to be installed as well as the CDI and antenna. IIRC, it took about 5 rounds of mailing paperwork back and forth with them to make the FSDO happy.

as far as the AC I was preaching about.

Here's the new one I think.

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC 20-138B.pdf
 
Jaybird180 said:
Reading another thread, there was discussion about substituting GPS (only in certain cases) for DME or ADF. What I don't understand is why are there restrictions on using GPS to identify where you are in 3 dimensional space,
Click to expand...
That's a rather technical issue you'd have to ask the FAA to explain.

what additional capabilities does having a "certified" GPS give the pilot
Click to expand...
The capabilities enumerated in the AIM sections 1-1-19 and 1-2-3.

and why are there ANY restrictions on using GPS in lieu of other equipment (twist on the first question).
Click to expand...
Because the FAA feels non-IFR-certified GPS's cannot be relied upon with sufficient confidence to be sufficiently accurate for IFR navigation purposes, and to warn of possible inaccuracy, under all reasonably foreseeable operating conditions.
 
flyingron said:
I can't vouch for your ordeal, but an IFR GPS installation is not that involved. You buy the unit and the STC. Install it and test according to the installation instructions, file the 337's and then it's VFR only until you do one approach on it. Then you sign that off and send the package over to the FSDO.
Click to expand...
The flight test requirements are a bit more complicated that "do one approach," but it doesn't take that long to accomplish -- like half an hour, I think, for my Garmin 530.
 
bartmc said:
I don't have an STC that I'm aware of. There's a new-ish AC out and I believe it requires 3 approaches now too. This project started March/April, 337s went in the mail on Tuesday.
Click to expand...
There should be an STC, but you may have missed it in the paperwork package prepared by the avionics shop which installed it. Look again -- it should be in there somewhere. If not, check with B/K or the avionics shop.
 
Ron Levy said:
There should be an STC, but you may have missed it in the paperwork package prepared by the avionics shop which installed it. Look again -- it should be in there somewhere. If not, check with B/K or the avionics shop.
Click to expand...

I have 2-337s one got mailed, a piece of paperwork for continued airworthiness and a AFM Supplement that has every page signed by the FAA. Wouldn't the STC be on file with the FAA? I only see 1 STC for the 89B and that's for a Mooney M20C.
 
bartmc said:
I have 2-337s one got mailed, a piece of paperwork for continued airworthiness and a AFM Supplement that has every page signed by the FAA. Wouldn't the STC be on file with the FAA? I only see 1 STC for the 89B and that's for a Mooney M20C.
Click to expand...
Check your 337 -- I'll bet it references that STC.
 
Ron Levy said:
Check your 337 -- I'll bet it references that STC.
Click to expand...

It's still at the hangar, I'll check it Sunday. I didn't look over the 337 too much, I took the AFM supplement and made a few copies so I have one here.
 
There is still a lot of misunderstanding on the process to get a GPS installed as certified for IFR. AC 90-138B describes the most current process. In the old days, each IFR GPS installation needed to be individually approved thru the field approval process. This was normally documented as a follow on to an existing STC for the VFR installation and required the FSDO to field approve the installation. Then, the sample AFMS provided by the manufacturer was edited by the installer to match the specific installation and this also had to be field approved using the 337 process to obtain IFR certification. As part of the VFR and IFR installation, flight tests were required.

As time went by, the FAA permitted the VFR installation to be performed as a minor modification, but the IFR approval still followed the same process unless there was an STC for the specific make and model of aircraft for the installation using a AML (Approved Model List) including an already FAA approved AFMS. Since most of the legacy GPS units did not have a STC with an AML, they still had to obtain IFR approval thru the field approval process (examples include the KLN90B and other King units, the GNS430 and 530, etc.). The GNS480 was one of the first to provide a STC with an AML and included a FAA approved AFMS. The GNS430W/530W also adopted this method, so did the GTN series, and all future GPS units will follow this process.

So if you have a legacy GNS430/530, KLN90B, KLN89B, KLN94, etc., you still have to use the old process for IFR approval, but you can install the unit as a VFR only unit without requiring a 337, just a log book entry. For the GNS430W/530W, GNS480, or GTN series, you can install it as a minor modification if the installation meets the requirements of the AC. Most will document the installation with a 337, but the FAA approved data is from the STC, and the FSDO does not get involved in the process. You just mail in the copy of the 337 to Oklahoma City for filing. To get the FAA approved AFMS, all you need to do is to print it out, fill in your aircraft data, check a few option boxes, and put it in the POH. No 337 is required to get it approved as it already is approved.
 
Ron Levy said:
That's a rather technical issue you'd have to ask the FAA to explain...

The capabilities enumerated in the AIM sections 1-1-19 and 1-2-3....

Because the FAA feels non-IFR-certified GPS's cannot be relied upon with sufficient confidence to be sufficiently accurate for IFR navigation purposes, and to warn of possible inaccuracy, under all reasonably foreseeable operating conditions.
Click to expand...

Sounds like you're saying the FAA doesn't trust GPS as much as other navigation systems (ADF, DME, VOR), hence the convoluted process and restrictions.

If this were true, then we've been sold a bill of good that (in their eyes) isn't so good (even in the face of WAAS and the upcoming WAAS2 - or whatever it will be called).
 
Jaybird180 said:
Sounds like you're saying the FAA doesn't trust GPS as much as other navigation systems (ADF, DME, VOR), hence the convoluted process and restrictions.

If this were true, then we've been sold a bill of good that (in their eyes) isn't so good (even in the face of WAAS and the upcoming WAAS2 - or whatever it will be called).
Click to expand...

Trust is a key issue. By its very nature, GPS position has the possibility of not meeting the accuracy requirements 100% of the time and it is essential that the pilot know when it cannot be counted on for a particular operation. Integrity checking is to provide a means of notifying the pilot when the GPS calculated position can't be trusted. One thing that a VFR GPS doesn't have is this function. For a non WAAS GPS, RAIM is used, for a WAAS GPS, the WAAS integrity data is used to determine integrity.

For ground based systems, there is some form of integrity information built in, for example the Ident audio code will go away if the station is off line or it is detected to be out of specification by the monitoring equipment.
 
It's not that the FAA doesn't trust GPS, it's that the non-certified devices do not include features for integrity monitoring that the FAA requires (this is a cost issue), and haven't been through the certification process to validate their operation (this is a BIG cost issue).

Toshiba commercials aside, these things just don't matter for the drivers and hikers.

They would matter, if for instance, you were going to have a self-driving car so Stevie Wonder won't need a chauffeur anymore.
 
John Collins said:
There is still a lot of misunderstanding on the process to get a GPS installed as certified for IFR. AC 90-138B describes the most current process. In the old days, each IFR GPS installation needed to be individually approved thru the field approval process. This was normally documented as a follow on to an existing STC for the VFR installation and required the FSDO to field approve the installation. Then, the sample AFMS provided by the manufacturer was edited by the installer to match the specific installation and this also had to be field approved using the 337 process to obtain IFR certification. As part of the VFR and IFR installation, flight tests were required.

As time went by, the FAA permitted the VFR installation to be performed as a minor modification, but the IFR approval still followed the same process unless there was an STC for the specific make and model of aircraft for the installation using a AML (Approved Model List) including an already FAA approved AFMS. Since most of the legacy GPS units did not have a STC with an AML, they still had to obtain IFR approval thru the field approval process (examples include the KLN90B and other King units, the GNS430 and 530, etc.). The GNS480 was one of the first to provide a STC with an AML and included a FAA approved AFMS. The GNS430W/530W also adopted this method, so did the GTN series, and all future GPS units will follow this process.

So if you have a legacy GNS430/530, KLN90B, KLN89B, KLN94, etc., you still have to use the old process for IFR approval, but you can install the unit as a VFR only unit without requiring a 337, just a log book entry. For the GNS430W/530W, GNS480, or GTN series, you can install it as a minor modification if the installation meets the requirements of the AC. Most will document the installation with a 337, but the FAA approved data is from the STC, and the FSDO does not get involved in the process. You just mail in the copy of the 337 to Oklahoma City for filing. To get the FAA approved AFMS, all you need to do is to print it out, fill in your aircraft data, check a few option boxes, and put it in the POH. No 337 is required to get it approved as it already is approved.
Click to expand...

Thanks, that's what my understanding was too, I did speak with the FSDO since i was getting different stories from everyone I talked to, so ultimately, I just called the guy at the FSDO that was going to sign his name to my paperwork. He told me for VFR usage.

"The installers are professionals, if they want to sign it off with a log book entry as a minor modification, we won't question that"

But, for IFR, I did have to submit a "plan" and the AFMS to the FSDO and have them sign off on it.

Curious enough, I went digging for STCs I see the GTN GPSes are STCed for about every aircraft known to man, the 89B only has an STC for a Mooney M20C.
 
John Collins said:
Trust is a key issue. By its very nature, GPS position has the possibility of not meeting the accuracy requirements 100% of the time and it is essential that the pilot know when it cannot be counted on for a particular operation. Integrity checking is to provide a means of notifying the pilot when the GPS calculated position can't be trusted. One thing that a VFR GPS doesn't have is this function. For a non WAAS GPS, RAIM is used, for a WAAS GPS, the WAAS integrity data is used to determine integrity.

For ground based systems, there is some form of integrity information built in, for example the Ident audio code will go away if the station is off line or it is detected to be out of specification by the monitoring equipment.
Click to expand...

Ignoring that you can install an IFR (TSO c129 or something) in a VFR manner, BUT. the FAA is also concerned about the system as a whole, they want those ARM,MSG,WPT lights blaring in your face and, IIRC, they have line of site requirements (complete with numbers and angles) on where the annunciator and possibly CDI should be placed. I think this would be a concern to a Bo pilot or the likes that has the stack WAY OVER THERE -------------> etc... I know I had to swap my CDIs around to make them happy, which sucks too because I can actually see the other CDI better even though it's farther away. I have to look down to see the GPS CDI and tilt my head sideways to see what course it's set to. And my installer used some "creative words" for how and where they wanted the annunciator installed.
 
Fearless Tower said:
Think of it like the stupid panel mounted clock requirement.....bureaucracy is a biotch.

Just like handheld timers, there are alot of much better reliable and capable handheld GPS units compared to some of the older panel mounted certified ones.
Click to expand...
To my knowledge there isn't a single handheld on the market that has the software necessary to do things like monitor VPL and HPL on an approach and alert the pilot WRT what mins apply. Nor do any that I know of have RAIM capabilities.
 
John Collins said:
For ground based systems, there is some form of integrity information built in, for example the Ident audio code will go away if the station is off line or it is detected to be out of specification by the monitoring equipment.
Click to expand...

First time I've heard that explained that way, thanks.
 
John Collins said:
For ground based systems, there is some form of integrity information built in, for example the Ident audio code will go away if the station is off line or it is detected to be out of specification by the monitoring equipment.
Click to expand...

That distinction is largely illusory. The ident goes away when a human puts it into maintenance mode or otherwise realizes it isn't working properly. Further, the navaid / receiver combination isn't able to detect a things like people parking vehicles in a way that interferes with the signal, p-static affect on ADF and LORAN, etc....

The truth is, that GPS is held to a higher standard than the ancient naiads because the FAA wants to hold it to a higher standard.
 
Jaybird180 said:
Sounds like you're saying the FAA doesn't trust GPS as much as other navigation systems (ADF, DME, VOR), hence the convoluted process and restrictions.
Click to expand...
If you're speaking of non-certified GPS's, that's correct, but that's no different than any other noncertified product used in a critical application, including engines, instruments, parts, etc. If you're speaking of certified GPS's, that's not true at all, since the FAA says I can launch IFR with the GPS portion of my TSO c146 certified GNS530W as the sole navigation system operational in my airplane.
 
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flyingron said:
That distinction is largely illusory. The ident goes away when a human puts it into maintenance mode or otherwise realizes it isn't working properly.
Click to expand...
That may be true for some navaids but not all. AFaIK many VOR, LOC, and GS transmitters have automatic monitoring systems that can remove the Ident without human intervention if something goes out of tolerance.
 
It's NOTAM'd when a Navaid is unmonitored.

(The logical assumption would then be that they all are unless NOTAM'd.)

This IEEE article appears to have discussed it in 1966.

http://ieeexplore.ieee.org/Xplore/l...266934.pdf?arnumber=5266934&authDecision=-203

Aeroflex test gear says it can be utilized to exercise the monitoring equipment...

http://www.aeroflex.com/ats/products/prodfiles/appnotes/901iss1.pdf

Here's a college student's paper about how to test the glideslope for refraction/interference from ground snow in 1995...

http://etd.ohiolink.edu/view.cgi/Marcum Frank.pdf?ohiou1174609165

And the best one of all isn't from FAA but from Australia's CASA. Section 3.4 defines the criteria for triggering the ILS alarms in the Tower...

http://www.casa.gov.au/wcmswr/_assets/main/pilots/download/ils.pdf

All from a Google search of "ILS monitoring". Not hard to find.
 
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