IFR/IMC flight with non-certified IFR equipment

My C172 is experimental due to a V8 engine, so I can use non-cert parts. I can not find specific FAA guidance regarding using experimental instruments or EFIS systems and filing IFR in IMC. the experimental equipment manufacturers seemed to be overly vague when asked if it would be legal. The only FAA regulations I could find simply say the equipment must meet the same requirements as certified.

specifically, my question relates to using GPS as a primary navigation for approach. I reference that certified units need a RNP alert or method to alert if navigation performance falls below a certain accuracy, such as .3, and deflection of flight director is more precise as altitude decreases, but if a manufacturer states that their unit meets same standards as listed in TSO for certified aircraft, is that enough for use in EXP aircraft? Would the pilot have to document such accuracy and compliance on his own?

What does your operating limitations say? This is where you must start.

Why would you want to risk your life on an instrument approach with a GPS that doesn't have proper integrity monitoring?

You have an experimental but it's not amateur built. What someone can do in a homebuilt (amateur built) may not apply to your plane which is why you should check the OL. Pretty sure you will never be flying RNP procedures so no need for RNP alerting.

My op limitations allow IFR if aircraft meets IFR requirements. This is same limitation as AB as far as I can tell, including same limitation reference # from FAA matrix. As far as RNAV GPS approaches go, my question is does anyone have any specific policy guidance in what the EXP owner would need to do to be compliant in using a non certified GPS as primary nav? My limits just require me to meet the requirements of 91.205(d), which does not mention equipment must be certified. Only other reference to GPS I can find is AC-138 which basically says GPS does not need to be manufactured under a TSO but it must meet same requirements, which would leave it up to aircraft owner to prove it meet meets same requirements.

so, question remains, does anyone have any experience on what owners have done to document compliance of a non certified GPS interface? As far as flying RNAV approach in IMC, I don’t intend to, but would like the legal ability to file IFR with GPS as primary navigation and maybe shoot RNP approach in VMC if available.

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Originally Posted by Skydawg

so, question remains, does anyone have any experience on what owners have done to document compliance of a non certified GPS interface?

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Owners have not done this because in order to prove that a non-TSO'd piece of equipment meets the requirements of a TSO, you'd have to go through the whole range of TSO testing. In which case, if you passed, just get the damn TSO. Since no experimental EFIS/GPS manufacturers (Dynon, Garmin, etc.) has done this, there must be a good reason - it's hard and a lot of work, and their equipment does NOT meet the TSO requirements (RAIM, etc.).

It's NOT legal to use non-TSO'd or non-TSO'd equivalent equipment for IFR, and no-one will tell you that a non-TSO'd piece of equipment meets the requirements of the TSO.

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Originally Posted by Skydawg

As far as flying RNAV approach in IMC, I don’t intend to, but would like the legal ability to file IFR with GPS as primary navigation and maybe shoot RNP approach in VMC if available.

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No can do. Either install a TSO'd navigator (GPS-175, GNS-650, Avidyne IFD-440, etc.) or don't shoot GPS approaches or use GPS as the primary navigational means enroute.

Now, since it's legal to use a ham sandwich as the primary means of IFR en-route navigation (i.e., pilotage, dead reckoning, etc.) as long as you file your route assuming that primary means, you can use any GPS (or anything else) as your SECONDARY means of navigation. But this only applies en-route.

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Originally Posted by Skydawg

so, question remains, does anyone have any experience on what owners have done to document compliance of a non certified GPS interface?

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The AIM is an excellent reference for navigation. It's states authorization to use GPS for any IFR operation is based on several factors like;

-- GPS navigation equipment must be approved in accordance with TSO-C129, or equivalent, and the installation must be done in accordance with Advisory Circular AC 20-138D or equivalent. (there's nothing in that AC that suggest an owner can prove his non-approved gear meets TSO then be good to go)

-- Aircraft using GPS for navigation under IFR may require an approved and operational alternate means of navigation appropriate to the flight.

-- The GPS operation must be conducted in accordance with the FAA-approved aircraft flight manual (AFM) or flight manual supplement.


Flying with non approved gear is not going to end well if there is loss of separation.

I had this conversation with a mx fed years ago. What he shared was that the only thing required to actually be TSO'd was a GPS to be used for terminal operations. If you as the builder say the equipment works as planned, and test / prove it in your phase one testing, there you go. That's why we have phase one, and after a mod like that the feds would want you to do another phase one period.
Something this fed added was that there were at least some Pipers built with non-certified instruments and that the plane as a whole, with those instruments installed, was certified. Very interesting stuff, and not something I'd have ever guessed.
Certainly the rules could have changed in the intervening time, so were I doing this I'd place a call to OSH and ask the guys that interface with the DC feds regularly and get their take on the current paradigm.

Marc is exactly correct. No TSO; no play with the certified/TSOd airplanes. The rules are not there for X-plane pilots; they are there to protect the ones playing legally in the NAS.

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Originally Posted by Ron Blum

Marc is exactly correct. No TSO; no play with the certified/TSOd airplanes. The rules are not there for X-plane pilots; they are there to protect the ones playing legally in the NAS.

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Actually, not fully correct. Regs say the GPS must meet same TSO as cert; not that user must have said testing data from manufacturer. FAA now uses performance based criteria to demonstrate compliance, so one could make a reasonable effort to prove it meets the same ELOS. I was wondering just how in depth this would be for a good avionics shop to reasonably perform. When I was a DER flight test pilot for big planes, much of the art of the certification plan was to do just that, find quickest (and cheapest) method to demonstrate compliance.

Additionally, any part 91 aircraft can file & fly IFR in VMC for training and checkride purposes legally.... without any IFR "certified" equipment. So even though my experimental C172 equipment (EFIS and GPS) is not "certified" as long as I stay VMC for training purposes.

Just wondering if anyone look more in depth about into the TSO angle