What certified GPS you need for IFR

[dynonsupport]

We often get asked at Dynon about what is required to use a GPS in IFR operations. One of the more common questions is if the installer can put a "certified GPS" in the airplane and make the whole EFIS legal for use in IFR. This has become more common as ADS-B has started to drive a market for small, standalone certified GPS position sensors that can feed ADS-B out devices.

For experimental EFIS customers that wish to build an instrument suite that allows the pilot to use GPS navigation as a primary reference in IFR, whether en-route or approach, it is Dynon Avionics' opinion that this cannot be done legally in the USA without a fully certified TSO-C129 or TSO-C146 GPS Navigator on board. A device which is only certified to TSO-C145 is not sufficient, and TSO-C145 is what any GPS module that does not have a screen and databases is certified to.


The reference that we base this opinion on most heavily is the AIM, which has the following statement:

1.[ch8194]Authorization to fly approaches under IFR using GPS avionics systems requires that:

(a)[ch8194]A pilot use GPS avionics with TSO- C129, or equivalent, authorization in class A1, B1, B3, C1, or C3; and

(b)[ch8194]All approach procedures to be flown must be retrievable from the current airborne navigation database supplied by the TSO-C129 equipment manufacturer or other FAA approved source. The system must be able to retrieve the procedure by name[ch8201]from the aircraft navigation database, not just as a manually entered series of waypoints.

and:

1.[ch8194]Authorization to conduct any GPS operation under IFR requires that:

(a)[ch8194]GPS navigation equipment used must be approved in accordance with the requirements specified in Technical Standard Order (TSO) TSO-C129, or equivalent, and the installation must be done in accordance with Advisory Circular AC[ch8201]20-138, Airworthiness Approval of Global Positioning System (GPS) Navigation Equipment for Use as a VFR and IFR Supplemental Navigation System, or Advisory Circular AC[ch8201]20-130A, Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors, or equivalent. Equipment approved in accordance with TSO-C115a does not meet the requirements of TSO-C129. Visual flight rules (VFR) and hand-held GPS systems are not authorized for IFR navigation, instrument approaches, or as a principal instrument flight reference. During IFR operations they may be considered only an aid to situational awareness.

It is our opinion that the above requires the navigation system as a whole to be certified, not just the GPS position sensor. TSO-C129 is titled "AIRBORNE SUPPLEMENTAL NAVIGATION EQUIPMENT USING THE GLOBAL POSITIONING SYSTEM (GPS)". The TSO defines a whole navigation system, including displays, databases, and the way you calculate the guidance given to the pilot based on the entered flight plan. The AIM does allow "equivalent" TSO's to be used, and in fact a modern product like a Garmin GTN is TSO'd to TSO-C146 "STAND-ALONE AIRBORNE NAVIGATION EQUIPMENT USING THE GLOBAL POSITIONING SYSTEM (GPS) AUGMENTED BY THE WIDE AREA AUGMENTATION SYSTEM (WAAS)".

We believe that just sourcing position from a certified position source, but not certifying your databases, display, user manual, serial parsers, cross track calculations, etc, does not pass the definition required in the AIM. There are specific TSO's for position sensors only, such as TSO-145, titled "AIRBORNE NAVIGATION SENSORS USING THE GLOBAL POSITIONING SYSTEM (GPS) AUGMENTED BY THE WIDE AREA AUGMENTATION SYSTEM (WAAS)". The fact that the FAA has different TSO's for position sensors and "navigation equipment" is evidence that they recognize that just having a certified GPS that knows where you are does not allow you to fly an apporach with it.

Dynon recognizes that the AIM is not a regulatory document like the FARs are, and is meant to be guidance for pilots, however, in this case the FAA's opinion is made very clear, and we do not believe that one could argue that an experimental EFIS with a TSO-C145 WAAS position sensor as it's location source could be authorized to fly GPS in IFR in any circumstance.

It does remain our opinion that if you have a TSO-C146 or C129 device on board, that displaying the output of that GPS in the from of CDI needle(s) on an Experimental EFIS is within the spirit and letter of the FARs.

 

[cthessen]

I would agree that a certified gps is necessary for ifr flight. My question is, if i have one, and if fails can the Dynon WAAS GPS be used in an emergency to execute a full LPV approach. Does the database download from Jepp for the Dynon Skyview have all the GPS instrument procedures in them and can they be maintained in currency to provide for an emergency backup, or would I need to buy another certified gps for that?

 

[Dynon]

SkyView's databases don't have the approaches in them, and there isn't a way to program something in ad-hoc. Vertical navigation / planning are features on our radar (pun intended) though, but we haven't commited to anything there yet. But if you ended up in IMC with a failed GPS navigation device, even if you didn't have a backup, having SkyView's situational awareness can be a lifesaver (having synthetic vision with terrain and runways, combined with the moving map, means that in a true emergency you could "fly the pictures" and end up saving yourself. In such a situation, of course, you'd really want to think about declaring, but between SkyView and some help from ATC, you have a pretty good emergency backup.

 

[carlmeek]

Dynon - Please could you give me a steer on the probability of VNAV and approaches being integrated into SkyView for use without a certified GPS?

I'm at a decision point - having purchased, designed and installed 3x Skyviews, AP-Panel, 2x SV COM, i'm feeling a little disappointed at lack of VNAV so am considering possibly buying a certified GPS.... but i'd rather not!!

 

[dynonsupport]

VNAV is a rather broad term. What specifically are you hoping SkyView could help you do?

 

[carlmeek]

Ha ha, sorry - yes - should be more specific.

My current aircraft with a Trio autopilot is pretty simple 2D autopilot that can follow the magenta line, all climbs and descends are manual.

It would be great for me if the new aircraft with skyview could do (in order of importance to me)

1. A 3D flight plan, descending and climbing over/under controlled airspace as per the flight plan i send it over WIFI or set directly into the skyview

2. Do a circuit pattern and GPS approach, home made is fine, but that would be the perfect autopilot ending to a flight if it could fly the pattern and set the aircraft on approach to the runway.

 

[dynonsupport]

Oh, is that all you want?

Enroute VNAV is the domain of full FMS systems, which general aviation GPS navigators are not. Generally only jets schedule their altitudes. It requires a lot of knowledge of climb and descent rates and aircraft performance. As far as I know, no GPS navigator (Garmin, Avidyne, Bendix-King) will let you schedule altitudes and send them to the autopilot.

Flying a pattern is also not really heard of since there's a reason IFR approaches look like they do, are the size they are, are fully surveyed, and aircraft spacing is much greater. Flying a pattern involves different entry directions, and variable leg lengths. How would you deal with the controller asking you to extend downwind for traffic, or to keep close?

So for now, I don't think Dynon is anywhere near to implementing the features you asked for, but you also won't get them if you do install a certified GPS navigator. Generically, VNAV means getting vertical guidance down the GPS glidepath on a fully surveyed GPS approach that is loaded in the database. They aren't of much use in the VFR domain unless you do want to start your approach 10 miles out.

This doesn't mean that we aren't interested in some VNAV capabilities, but I don't think they will align with your needs in the near term. It's an interesting discussion and we'd love to hear any other ideas, use cases, or solutions to problems people have.

 

[RVDan]

The Garmin G1000 will couple VNAV but only for enroute and with limitations.  Of course $300K or so will get you just a bit more.  But seriously, even the FMS's for some of the large airplanes won't couple VNAV. 


IMO, the closer to the pattern I get (VFR) the more I want my hands on the controls for last minute see and avoid maneuvers.  Transitioning from the AP to hand flying takes a few seconds and you may not have that when in close to other traffic. 

 

[carlmeek]

That all makes a lot of sense - thanks

In the UK we have some fascinating airspace, for example around heathrow. For VFR routings we often have to dive under 1500 zones, then back up to under 2500, then higher.

It would be great for these uncontrolled complex routings to have the AP automatically follow defined altitudes.

SkyDemon software has a fantastic feature for the planning and flying of these - see picture, it's the lower panel. You can drag sectors between waypoints up and down to different altitudes, thereby avoiding controlled airspace. It automatically does the climb/descend angle based on a simple standard parameter of Feet/Min. So it looks like a "connect the dots" logical move for Skydemon to WIFI this to the Skyview and then AP to fly it automatically

Apparently several of the big certified EFIS systems CAN do this - G3000 can, and from another forum apparently the Advanced AFS 5600 can do it too?