Fitting "non certified" avionics as secondary instruments
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Fitting "non certified" avionics as secondary instruments
I was wondering whether it is possible to fit some of these non-certified avionics found in may permit aircraft to a CofA aeroplane as a "standby instrument"? For example one can pick up a pretty funky Dynon Skyview system for under 3000 GBP from Harry M's, which is cheaper than a certified MFD. If you could fit one of these in the P2 position as a "secondary" instrument, would this be legal. I'm thinking G reg and N reg here.
Some amazing pieces of kit out there a tenth the price of a G500, so it would make sense to have these as "backup" instruments while retaining the old instruments. I assume that as long as it didn't interfere with the certified avionics then it should be ok?
Ok, if it is NOT ok, then why can't one get an STC to fit one as a standby instrument, exactly the same was as JPI do with their range of EDM secondary engine monitors? I imagine if this was done under the FAA then the costs would be relatively low and fairly easy....??
Some amazing pieces of kit out there a tenth the price of a G500, so it would make sense to have these as "backup" instruments while retaining the old instruments. I assume that as long as it didn't interfere with the certified avionics then it should be ok?
Ok, if it is NOT ok, then why can't one get an STC to fit one as a standby instrument, exactly the same was as JPI do with their range of EDM secondary engine monitors? I imagine if this was done under the FAA then the costs would be relatively low and fairly easy....??
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Why not fit them anyway (as a standby system of course!), and then placard them, in nice big letters, "inop" or "not for aviation use"?
Remove them when it's annual check time, and replace them after........ then everyone is happy!!!!
Tin Hat on, standing by for "Incoming" !!!
I'm reading Geoffrey De Havilland's autobiography at the moment (Sky Fever). He describes the situation when they had devised an aero engine with a new dual ignition system (all engines up to then had single ignitions). The Ministry wallas got involved and decreed that, for safety(?!) reasons, the dual ignition had to be disabled to a single ignition (by removing a plug lead I guess) for all flights further than 3 miles from the airfield. The system could be used inside the 3 mile limit??!! This was in the early 1920s...............Kind of comforting to think that after 80+ years, things haven't changed eh?
Jez
Remove them when it's annual check time, and replace them after........ then everyone is happy!!!!
Tin Hat on, standing by for "Incoming" !!!
I'm reading Geoffrey De Havilland's autobiography at the moment (Sky Fever). He describes the situation when they had devised an aero engine with a new dual ignition system (all engines up to then had single ignitions). The Ministry wallas got involved and decreed that, for safety(?!) reasons, the dual ignition had to be disabled to a single ignition (by removing a plug lead I guess) for all flights further than 3 miles from the airfield. The system could be used inside the 3 mile limit??!! This was in the early 1920s...............Kind of comforting to think that after 80+ years, things haven't changed eh?
Jez
Last edited by cambioso; 27th Nov 2010 at 07:29. Reason: Spelling!
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It is very difficult to get an authoritative view on this kind of thing, and of course it varies between states of registry anyway.
My understanding is as follows, for N-regs:
In general to do a mod on an ICAO CofA plane you need Approved Data for the item in question.
Approved Data can be a Type Certificate (so if the item was on the original type certificate, for the right airframe S/N range, you can just install it at any later date, with just a logbook entry), a Supplementary Type Certificate (you need to apply for approval for this e.g. an FAA 337 but this almost invariably won't be refused), a design done by an FAA DER (comment as previous), a TSO or PMA approval of the item (this is more tricky because the TSO/PMA is unlikely to specify the whole installation environment), etc.
Or you can go through FAR Part 43 Appendix A (the list of Major Mods), and all the various guidance notes, and if it is not in there then by definition (**) you can install it as a Minor Mod, with just a logbook entry.
It is completely standard and in accordance with proper US/FAA practice, to do Minor Mods using TSOd items, with just a logbook entry and appropriate documentation in the work pack (load analysis, W&B). I think you could install a genuine backup instrument, using TSOd parts, in this way, anytime, and any A&P/IA (who can read Part 43 Appendix A) will sign it off. And example would be a backup oil pressure gauge system made up of TSOd parts (sensor and indicator); this is one area I have researched in detail.
The fact that something is a Minor Mod does not do away with the need for component traceability so everything needs to come with a suitable document, which can be an EASA1, 8130-3, or any other bit of paper which provides traceability information (***). You can't just buy something from B&Q, although if you got the exact same item with a TSO/PMA and a Certificate of Conformity showing a batch # then you could.
Obviously there are grey areas around the corners of what is a Minor Mod, and these move according to who is trying to make money out of who. One long standing one was the installation of the superior Concorde solid-gel batteries in place of the old liquid acid Gill ones. To deal with the widespread installer illiteracy and for marketing reasons, Concorde got various (trivial) STCs, but eventually the FAA ruled that the swap can be done with just a logbook entry and that is now the US practice (which is great news). But these batteries are properly aviation-approved so you do have that bit of Approved Data; you could not fit a car battery from Halfords.
A bit of homebuilt-category avionics like a Dynon is a problem because it has not even a TSO or PMA approval (AIUI). You would need to pay a DER to generate Approved Data. I have never heard of anybody doing that; I guess it would be nontrivial. I have researched a fixed satellite phone installation and that was what I found; Iridium have the market sewn up, with several "approved" products.
If the Dynon had TSO or PMA then it can do it, with proper documentation etc. I do think there are issues otherwise everybody would be doing it. A TSO does not mean much, and certainly no GA aviation approval means anything w.r.t. reliability or design quality, but it does cost money. I looked at getting a PMA approval for something I was going to manufacture and it was very hard for a non-US business to get, largely due to the need to host a load of American officials for a while, while they inspect your factory.
The way to avoid all this crap is to make the item "temporarily" mounted e.g. velcro. The FAA did try recently to stop more "obviously permanent" GPS installations which use e.g. a yoke mounting bracket but they backed off under the sh*tstorm which ensued as that would have killed most of the portable aviation GPS market
(**) It is customary for the big UK avionics shops, and the less "educated" US avionics shops who can't read the regs, to disregard this and treat everything they do as a Major Mod, pay a DER, send off a 337, etc. This obviously increases the cost substantially. The FAA has said in various seminars they don't like this, and the other day one US avionics installer told me they have had 337s returned by the FAA on grounds of triviality. But the practice continues, and going to a DER is a "safe" CYA procedure which cost a few hundred bucks per signature (a DER won't return an application on grounds of trivia because he makes a living that way).
(***) This is a ripe area for disinformation and revenue generation, with items "requiring" and EASA1 form selling for 2x as much
and this is true for both FAA and EASA rules.
My understanding is as follows, for N-regs:
In general to do a mod on an ICAO CofA plane you need Approved Data for the item in question.
Approved Data can be a Type Certificate (so if the item was on the original type certificate, for the right airframe S/N range, you can just install it at any later date, with just a logbook entry), a Supplementary Type Certificate (you need to apply for approval for this e.g. an FAA 337 but this almost invariably won't be refused), a design done by an FAA DER (comment as previous), a TSO or PMA approval of the item (this is more tricky because the TSO/PMA is unlikely to specify the whole installation environment), etc.
Or you can go through FAR Part 43 Appendix A (the list of Major Mods), and all the various guidance notes, and if it is not in there then by definition (**) you can install it as a Minor Mod, with just a logbook entry.
It is completely standard and in accordance with proper US/FAA practice, to do Minor Mods using TSOd items, with just a logbook entry and appropriate documentation in the work pack (load analysis, W&B). I think you could install a genuine backup instrument, using TSOd parts, in this way, anytime, and any A&P/IA (who can read Part 43 Appendix A) will sign it off. And example would be a backup oil pressure gauge system made up of TSOd parts (sensor and indicator); this is one area I have researched in detail.
The fact that something is a Minor Mod does not do away with the need for component traceability so everything needs to come with a suitable document, which can be an EASA1, 8130-3, or any other bit of paper which provides traceability information (***). You can't just buy something from B&Q, although if you got the exact same item with a TSO/PMA and a Certificate of Conformity showing a batch # then you could.
Obviously there are grey areas around the corners of what is a Minor Mod, and these move according to who is trying to make money out of who. One long standing one was the installation of the superior Concorde solid-gel batteries in place of the old liquid acid Gill ones. To deal with the widespread installer illiteracy and for marketing reasons, Concorde got various (trivial) STCs, but eventually the FAA ruled that the swap can be done with just a logbook entry and that is now the US practice (which is great news). But these batteries are properly aviation-approved so you do have that bit of Approved Data; you could not fit a car battery from Halfords.
A bit of homebuilt-category avionics like a Dynon is a problem because it has not even a TSO or PMA approval (AIUI). You would need to pay a DER to generate Approved Data. I have never heard of anybody doing that; I guess it would be nontrivial. I have researched a fixed satellite phone installation and that was what I found; Iridium have the market sewn up, with several "approved" products.
If the Dynon had TSO or PMA then it can do it, with proper documentation etc. I do think there are issues otherwise everybody would be doing it. A TSO does not mean much, and certainly no GA aviation approval means anything w.r.t. reliability or design quality, but it does cost money. I looked at getting a PMA approval for something I was going to manufacture and it was very hard for a non-US business to get, largely due to the need to host a load of American officials for a while, while they inspect your factory.
The way to avoid all this crap is to make the item "temporarily" mounted e.g. velcro. The FAA did try recently to stop more "obviously permanent" GPS installations which use e.g. a yoke mounting bracket but they backed off under the sh*tstorm which ensued as that would have killed most of the portable aviation GPS market
(**) It is customary for the big UK avionics shops, and the less "educated" US avionics shops who can't read the regs, to disregard this and treat everything they do as a Major Mod, pay a DER, send off a 337, etc. This obviously increases the cost substantially. The FAA has said in various seminars they don't like this, and the other day one US avionics installer told me they have had 337s returned by the FAA on grounds of triviality. But the practice continues, and going to a DER is a "safe" CYA procedure which cost a few hundred bucks per signature (a DER won't return an application on grounds of trivia because he makes a living that way).
(***) This is a ripe area for disinformation and revenue generation, with items "requiring" and EASA1 form selling for 2x as much
and this is true for both FAA and EASA rules.
englishal
If it's for a G reg aircraft then suggest you contact the Yakovlevs: The Yakovlevs Aerobatic Display Team 2009
Their aircraft are fitted with Dynons following a minor mod approval from the CAA.
If it's for a G reg aircraft then suggest you contact the Yakovlevs: The Yakovlevs Aerobatic Display Team 2009
Their aircraft are fitted with Dynons following a minor mod approval from the CAA.
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It is not OK on a UK reg. and obtaining a minor mod. will almost certainly prove expensive and time consuming. I have been there.
I am not saying it cant be done and depending on the installation the hassle may diminish but it is not to be taken on lightly.
If you find someone to just "do it", you risk more problems when the annual is due.
Even "removable" equipment can be an issue unless of course you remove it before the annual!
I wish it were otherwise but better to tell you how I found it.
I am not saying it cant be done and depending on the installation the hassle may diminish but it is not to be taken on lightly.
If you find someone to just "do it", you risk more problems when the annual is due.
Even "removable" equipment can be an issue unless of course you remove it before the annual!
I wish it were otherwise but better to tell you how I found it.
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If I find an unapproved bit of kit at maintenance check I am bound by law to remove it before the aircraft can be released for service.
I suspect but cant prove that some kit gets removed from aircraft before I see the aircraft for a maintenance check and then refitted after the aircraft has gone back to the owner. This is of course not leagal but I cant the aircraft under survalance 24 hours a day!
I suspect but cant prove that some kit gets removed from aircraft before I see the aircraft for a maintenance check and then refitted after the aircraft has gone back to the owner. This is of course not leagal but I cant the aircraft under survalance 24 hours a day!
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If the kit is removable then it is not illegal, however
A piece of panel mounted avionics is not likely to be removed for the Annual, because it would leave a big hole in the panel, plus the cable connector.
And if a bit of kit is removable then it should not be illegal to do the Annual with it present... no?
Historically, in a typical 30 year old spamcan, a lot of items would have been installed without the right paperwork, years ago. A MO is entitled to assume that they went in legally even if the logbooks all the way back to 1980 don't exist. Presumably, A&C, you are referring to some really obvious installation of say a Garmin 296 screwed into the panel?
A piece of panel mounted avionics is not likely to be removed for the Annual, because it would leave a big hole in the panel, plus the cable connector.
And if a bit of kit is removable then it should not be illegal to do the Annual with it present... no?
Historically, in a typical 30 year old spamcan, a lot of items would have been installed without the right paperwork, years ago. A MO is entitled to assume that they went in legally even if the logbooks all the way back to 1980 don't exist. Presumably, A&C, you are referring to some really obvious installation of say a Garmin 296 screwed into the panel?
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If the kit is removable then it is not illegal
I suspect if you leave it in place you may still have issues at the annual depending how it is installed.
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I would not be so certain.
I suspect if you leave it in place you may still have issues at the annual depending how it is installed.
I suspect if you leave it in place you may still have issues at the annual depending how it is installed.
But they are installed - you have to plug 'em in!
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Using the case of a type certified aircraft in North America, operating under the flight authority of a standard C of A, the following requirements must be met: (my words)
A pilot may not attempt to fly an aircraft which does not conform to it's type design. It is either the original C of A, or the revalidation of that C of A by qualified inspection which confirms the conformance to it's type design at the required intervals.
When the plane leaves the factory, only approved and certified (as conforming to their type design, and thus being worthy), "pieces of kit" will be installed. There after, only similarly certified "pieces of kit" which are approved on that aircraft, may be installed, or you are invalidating the measure of "conform to type design", and thus the C of A.
The fact that something is certified as airworthy, TSO'd etc. does not automatically qualify it for installation in any aircraft. A Gramin 430 is "certified" and obviously commonly approved for installation in lots of aircraft types - but not helicopters after they leave the factory, other than by special approval. A tire will be TSO'd, and thus certified, and it might be the right size to fit your aircraft, but that does not make it's installation legal (conforming). It might be the wrong ply rating. The TSO'd tire, battery etc. still must be approved as a part of the type design.
Generally any change to the aircraft which has "other than a negligible effect" (those are government words, not mine) requires an approval.
If you're attaching your hand held GPS to the gawd awful transformer robot mount that grips the control column tube, and you do it right, and check everything moves as it should/shouldn't, you're probably okay, though do remind yourself that the instructions will say in there somewhere, that you must assure that you have not affected the safety of flight. If you don't think of something, and have an accident, you the installer pilot will suddenly be repsonsible for flying an unairworthy aircraft. In turbulance, could the GPS flip back, and jam full nose down control? Might the "temporary" GPS installation block the normal view of a gear unsafe light? I have seen many pilot/owner installed mods which definately would not be considered "minor", and would certainly require an approval or certification to be "airworthy".
The rule of thumb used by Transport Canada locally is that if a tool is required to perform the installation, or it wires into other than the cigarette lighter socket, it probably requires an approval.
There are lots of very worthwhile "things" which might be installed in an aircraft, which no one has yet approved. It does not make them not worthwhile, they are just not proven as conforming to the required type design yet.
A pilot may not attempt to fly an aircraft which does not conform to it's type design. It is either the original C of A, or the revalidation of that C of A by qualified inspection which confirms the conformance to it's type design at the required intervals.
When the plane leaves the factory, only approved and certified (as conforming to their type design, and thus being worthy), "pieces of kit" will be installed. There after, only similarly certified "pieces of kit" which are approved on that aircraft, may be installed, or you are invalidating the measure of "conform to type design", and thus the C of A.
The fact that something is certified as airworthy, TSO'd etc. does not automatically qualify it for installation in any aircraft. A Gramin 430 is "certified" and obviously commonly approved for installation in lots of aircraft types - but not helicopters after they leave the factory, other than by special approval. A tire will be TSO'd, and thus certified, and it might be the right size to fit your aircraft, but that does not make it's installation legal (conforming). It might be the wrong ply rating. The TSO'd tire, battery etc. still must be approved as a part of the type design.
Generally any change to the aircraft which has "other than a negligible effect" (those are government words, not mine) requires an approval.
If you're attaching your hand held GPS to the gawd awful transformer robot mount that grips the control column tube, and you do it right, and check everything moves as it should/shouldn't, you're probably okay, though do remind yourself that the instructions will say in there somewhere, that you must assure that you have not affected the safety of flight. If you don't think of something, and have an accident, you the installer pilot will suddenly be repsonsible for flying an unairworthy aircraft. In turbulance, could the GPS flip back, and jam full nose down control? Might the "temporary" GPS installation block the normal view of a gear unsafe light? I have seen many pilot/owner installed mods which definately would not be considered "minor", and would certainly require an approval or certification to be "airworthy".
The rule of thumb used by Transport Canada locally is that if a tool is required to perform the installation, or it wires into other than the cigarette lighter socket, it probably requires an approval.
There are lots of very worthwhile "things" which might be installed in an aircraft, which no one has yet approved. It does not make them not worthwhile, they are just not proven as conforming to the required type design yet.
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We have a garmin Aera 550 as VFR GPS (as a backup to the 430). This is wired into the aircraft power through a CB and has a hull mounted antenna. It is mounted on the Garmin aviation mount which is screwed to the throttle quadrant behind the levers and the wires are routed behind the plastics and carpets to it is a nice installation. To remove the Aera you pop it from the backet and take it home. However the bracket is permanently mounted to the throttle quadrant plastics with the wires permanently routed. There is also a data port mounted in the dash to connect to a Zaon as well as USB.
This is signed off by an FAA IA on a 337 so I guess should be legal? (it was installed by an avionics engineer and our maintenace co. so don't worry about fouling levers with the wires, it was done properly).
This is signed off by an FAA IA on a 337 so I guess should be legal? (it was installed by an avionics engineer and our maintenace co. so don't worry about fouling levers with the wires, it was done properly).
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or it wires into other than the cigarette lighter socket
I agree re doing it properly which is why I would never use a traditional yoke mount. The awful yoke mount which comes with a Garmin 496 is OK for a Russian combine harvester and that's about it. However, doing a job properly is not the same as it being legal...
other than a negligible effect
Taken literally (which is more or less the EASA line) this is the same as saying that an A&P or an IA is dumb, cannot read, has no idea how a plane works, and has no authority to sign off any mod other than a Type Certificated add-on accompanied by full drawings for that specific serial number range airframe. Yet, the foregoing text is simply not the actual practice in FAA-land.
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Un-approved equipment
On EASA aircraft, all components fitted to the aircraft other than standard parts (mil-spec hardware etc) must be released on an EASA Form 1 or equivalent - regulation 21A.307. Therefore installation of non-approved kit into a certified aircraft is a non-starter - and doing so voids the C of A and insurance. Look out if you have a non-approved modifcation in your aircraft and try to make a claim following an accident!
There are methods for non-ETSO equipment to be used, but this will be when the equipment normally has an FAA TSO and comes with an FAA 8130-3, and the equipment will then be approved via an EASA Part 21J DOA or directly by an EASA minor change. Other totally un-approved parts can also be got onto an aircraft but then it's via an EASA STC ( and for the hassle involved, it's not worth attempting).
In the case mentioned of the Dynon in Yaks, the YAK52 is an Annex 2 aircraft - it's on a CAA permit and not an EASA C of A, so 21A.307 doesn't apply, in exactly the same way as for ex-UK military aircraft. The Dynon isn't fufilling any mandatory requirement as the aircraft is Day VFR so carriage of an artificail horizon is not required.
On N reg aircraft and the comment by IO-540 about un-necessary Form 337s when the change could be classified as Minor and done as a logbook entry. Most A/Ps & IAs that I know won't clear a mod as a minor change unless the work is a direct form/fit/function swap of one box for another, such as changing a King KT76A transponder for a Trig Mode S unit or a like-for like upgrade of an ELT from 121.5 to 406. Beyond this, they expect changes to be covered on a Form 337 as a Major alteration. A 337 requires approved data, and this can be either from a DER on an 8110-3 (this is how we typically work), an FAA STC or by having the FAA FSDO sign the 337, which I don't believe happens outside the US. Therefore, the additonal costs incurred for a DER approval, whilst not always desireable, are in many cases the only method to get the mod signed off.
There are methods for non-ETSO equipment to be used, but this will be when the equipment normally has an FAA TSO and comes with an FAA 8130-3, and the equipment will then be approved via an EASA Part 21J DOA or directly by an EASA minor change. Other totally un-approved parts can also be got onto an aircraft but then it's via an EASA STC ( and for the hassle involved, it's not worth attempting).
In the case mentioned of the Dynon in Yaks, the YAK52 is an Annex 2 aircraft - it's on a CAA permit and not an EASA C of A, so 21A.307 doesn't apply, in exactly the same way as for ex-UK military aircraft. The Dynon isn't fufilling any mandatory requirement as the aircraft is Day VFR so carriage of an artificail horizon is not required.
On N reg aircraft and the comment by IO-540 about un-necessary Form 337s when the change could be classified as Minor and done as a logbook entry. Most A/Ps & IAs that I know won't clear a mod as a minor change unless the work is a direct form/fit/function swap of one box for another, such as changing a King KT76A transponder for a Trig Mode S unit or a like-for like upgrade of an ELT from 121.5 to 406. Beyond this, they expect changes to be covered on a Form 337 as a Major alteration. A 337 requires approved data, and this can be either from a DER on an 8110-3 (this is how we typically work), an FAA STC or by having the FAA FSDO sign the 337, which I don't believe happens outside the US. Therefore, the additonal costs incurred for a DER approval, whilst not always desireable, are in many cases the only method to get the mod signed off.
Last edited by wigglyamp; 27th Nov 2010 at 16:14. Reason: Correcting typos.
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Could you get a DAR to sign off a Dynon system as "secondary instrumentation" though? If a DAR costs 1000 quid (being generous here!) and the Dynon 3500 quid then you could end up with a neat secondary instrument package relatively cheaply (in aviation terms)....? This would give stdby AI, DI, MFD all in one hit.
Some of the non-approved MFDs are half the price of an "approved" one, yet probably contain much the same electronics.
In the case of our Aera, it is only the power supply and antenna installation which needs a sign off, which is a pretty standard thing to sign off (antenna location and mounting, power supply and CB choice).
Some of the non-approved MFDs are half the price of an "approved" one, yet probably contain much the same electronics.
In the case of our Aera, it is only the power supply and antenna installation which needs a sign off, which is a pretty standard thing to sign off (antenna location and mounting, power supply and CB choice).
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Fitting any form of EFIS in an FAA-certified aircraft will be based on FAA AC23-1311-1B. An EFIS attitude indicator is automatically an STC just as it is with EASA, so a DER isn't going to sign it off. The equipment must have a hardware and software Design Assurance Level C as defined in AC23-1309-1D, so there is no way to put un-certified EFIS which has none of the required equipment qualification in a certified platform - sorry!.
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Taken literally (which is more or less the EASA line) this is the same as saying that an A&P or an IA is dumb, cannot read, has no idea how a plane works, and has no authority to sign off any mod other than a Type Certificated add-on accompanied by full drawings for that specific serial number range airframe.
That said, every type certificate contains a section called "certification basis". This defines what is the minimum design standard applicable to that type, and that becomes the minimum standard to which any mod must also qualify, and demonstrate compliance. Though I agree that "mechanics" are very skilled, it is possible that they are not a conversant with the design standards, and how they are to be interpreted, and applied. That's where the FAA "DER" or TC "DAR" (very similar roles) come in.
Added to this, you will see a statement at the bottom of STC's requiring the installer to assure that the installation of that mod, does not create an unsafe condition in the context of the other mods which may already be installed on the aircraft. This is because the original type design showed compliance, and the first STC did also, but it is very possible that the second STC was not assessed for design compliance in the context of the aircraft with the first STC installed, the permutations would be very numerous!
An example of this would be; could you install a Horton STOL kit on a Cessna 185, which already has a Robertson STOL kit installed? Surprisingly, in some cases, yes! In an other case, I specifically approved such an installation.
Another much less comfortable example is the installation of an STC apporved TCM 550 engine to on a Cessna 180, in place of the O-470. The 550 has a much greater fuel flow, but the 180 airframe has demonstrated that it can provide that fuel, so compliance with the fuel flow requirement was found. However, the "least favourable attitude for fuel flow" used was probably not the higher pitch attitude attainable with a STOL kit, or VG kit. Yet there are many examples of aircraft with combined mods. I can tell you from personal experience, that in at least two Cessna 180's so modded, it is possible to fly the aircraft at full power at a pitch attitude so high (and much higher that the original) that fuel flow for the larger engine cannon be maintained, and it quits. 'Been there, done it! This is exactly the situation which could exist with a pilot straining the plane over the trees on takeoff - and then it quits!
The installer of the second STC, had not considered the iner-relationship of the second STC, with the first, and an unsafe, and non compliant aircraft was the result.
I realize that this is a far extreme situation from that presented in the original poster, but it is important to conssider that a DER/DAR is the person who's job it is to establish that ALL applicable design requirements for a mod have been considered, and met. "Mechanics" perhaps can do this, DER/DAR must!
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I suspect that if wigglyamp's reply correctly ties the Dynon product to the FAA EFIS (337 needed, etc) requirement, then that is the end of that... no practical way to do it.
Otherwise, loads of "backup" instruments are installed in the USA as a minor mod. You can install a backup altimeter (TSOd obviously) in that way. Backup engine instruments, likewise.
The thing which catches out a lot of people is that a lot of engine instruments are not certified as "primary" so the original gauge has to stay - even if it is useless. In my TB20, the EDM700 is certified as primary so no other CHT/EGT gauge is present, but on the TB21 the original CHT/EGT gauge has to stay...
In practice, there are holes in all this, potentially. I know of Skytec starter motors with an STC for aircraft X but which draw about 3x more current than the relay(s) can carry, and they get welded...
Otherwise, loads of "backup" instruments are installed in the USA as a minor mod. You can install a backup altimeter (TSOd obviously) in that way. Backup engine instruments, likewise.
The thing which catches out a lot of people is that a lot of engine instruments are not certified as "primary" so the original gauge has to stay - even if it is useless. In my TB20, the EDM700 is certified as primary so no other CHT/EGT gauge is present, but on the TB21 the original CHT/EGT gauge has to stay...
In practice, there are holes in all this, potentially. I know of Skytec starter motors with an STC for aircraft X but which draw about 3x more current than the relay(s) can carry, and they get welded...
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FAA guidance
The following is an extract from FAA AC23-1311-1B. You can see that the FAA anticipated applicants wanting to install EFIS-type displays as secondary instruments without going through the STC process and have cut that out immediately.
8.1
b. There have been applications to install equipment, such as flight and navigation displays, as non-required. These applications request approval for these installations as Situation Awareness (SA) only. It is not acceptable to label an instrument as "SA-Only" and assume that its failure condition is acceptable. Installing compelling displays that provide Primary Flight Information (PFI), but do not meet the appropriate operational and airworthiness requirements, and labeling them as "Supplemental" or "SA-Only" is not acceptable. Section 13.6 provides more guidance.
c. The basis for certification has been that the equipment should perform its intended function and not present a hazard. Instruments that aid situation awareness should be certified under the part 23 requirements, including § 23.1301 and § 23.1309. These displays could provide hazardous misleading information. PFI is essential for safe operation. An instrument that provides PFI should meet the minimum standards of applicable TSOs or an equivalent standard. It also should meet the guidance in AC 23.1309-1C, AC 23-17B, and the guidance in this AC.
8.1
b. There have been applications to install equipment, such as flight and navigation displays, as non-required. These applications request approval for these installations as Situation Awareness (SA) only. It is not acceptable to label an instrument as "SA-Only" and assume that its failure condition is acceptable. Installing compelling displays that provide Primary Flight Information (PFI), but do not meet the appropriate operational and airworthiness requirements, and labeling them as "Supplemental" or "SA-Only" is not acceptable. Section 13.6 provides more guidance.
c. The basis for certification has been that the equipment should perform its intended function and not present a hazard. Instruments that aid situation awareness should be certified under the part 23 requirements, including § 23.1301 and § 23.1309. These displays could provide hazardous misleading information. PFI is essential for safe operation. An instrument that provides PFI should meet the minimum standards of applicable TSOs or an equivalent standard. It also should meet the guidance in AC 23.1309-1C, AC 23-17B, and the guidance in this AC.