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Can any European-reg homebuilts / Annex 1 use homebuilt avionics?

Obviously not if there is transmission involved e.g. radios, transponders, DME, ADS-B OUT.

But what about things like fuel totalisers, engine monitors, etc?

What is the position of the UK LAA on this?

Shoreham EGKA, United Kingdom

Here there are some restrictions on homebuilt
IiRC they amount to things like a radio must be 8.33. Not sure about a transponder. All other avionics are at the owners prerogative as is the engine provided it is no more than 200 hp although if I remember correctly it is actually written on the rules as KW. There is also a maximum 4 seat rule. In kit form it comes under CNSK if built from plans it would come under the experimental category.


To me, putting an MGL, Dynon or home made instrument makes zero difference. It is the point of experimentals. A typical french homebuild (jodel) is worth a dynon suite

Edit : for 200+hp, the builder must provide a structural design document. Not a huge deal apparently.

Last Edited by Jujupilote at 08 Jan 17:09

Everything can be homebuilt. But with certain stuff such as radio, transponders, IFR avionics etc, you have to document performance according to standards. The simplest and cheapest way to do that (by far) is to get standard certified off the shelf equipment.

I remember when purchasing a radio. Certification was irrelevant, the only relevant thing was approval by NKOM (national radio communication bureau). The problem is, they have since long stopped doing the physical approval themselves, that is done by the manufacturers, they only look at documents. A ground station or a handheld, no problems, but no non certified aviation radio for mounting in the panel that is also approved by NKOM exists. Certified stuff is approved by default (well documented). In theory you can make a radio on your kitchen table, but them you also have to document performance according to NKOM (or the corresponding national bureau).

In practice it makes no sense to build stuff that needs to be approved according to a standard yourself, unless you really know what you are doing, and know the standards inside out, as well as all test procedures, and have all required testing equipment, and have an interest in doing it simply “because you can”. A Trig radio or similar is only 1.5-2k anyway. It’s exactly the same principle with a transponder, but a transponder has no other uses than aviation. Hence the only standards are aviation standards. So even if you make it yourself, it still needs to be “certified” as far as testing and documentation goes.

Besides, some things you (normally) just want them to work 100% with a minimal of fiddling, like engine and core instruments.


For LAA aircraft in the UK, there are some specific approval requirements given in the Tech Leaflets:

All transmitting radio equipment including portable equipment and transponders installed in UK aircraft must be of a type that has undergone an appropriate approval process by either EASA, the CAA or the FAA. In the case of equipment approved by the FAA, it must also be checked that the equipment meets European requirements that may not apply in the USA, e.g. 8.33Khz spacing for radios. For the purposes of LAA aircraft, this equipment must have either a CAA approval number, an EASA ETSO approval number or an FAA TSO. Usually the equipment manufacturer or importer will have dealt with this matter.

TL_3_03_Avionics_Installations local copy

Last Edited by wigglyamp at 09 Jan 09:48
Avionics geek.
Somewhere remote in Devon, UK.

Indeed; that is transmitting equipment, which one would expect to be regulated. However, the same document states

so it does look like an LAA inspector cannot refuse the installation of a homebuilt fuel totaliser, for example. I guess he might object to the installation in the fuel pipe, but normally one would do that exactly as the certified installation… why not?

Shoreham EGKA, United Kingdom

It depends on whether it’s a design change or not. The LAA told me when I asked that other than transmitting things, instruments are not a design change and just need an inspector signoff. They just need to be “fit for purpose”. I suspect putting the fuel flow measuring device into the fuel system would, however, require an LAA engineering review (you’re making a minor design change to the fuel system) but it’d be a minor one (I’d have to as LAA engineering).

I’ve not seen anything from the LAA about home built (non-transmitting) instruments.

If whatever you’re installing is done properly, no LAA inspector will object to it. LAA inspectors are not ogres (and they are not employed by the LAA), they are essentially freelance mechanics. All the LAA inspectors I know are in the business of getting stuff done, not stopping things from being done, the ones I know all have a “can do” attitude. Show them something that is done properly and they’ll never have a problem signing off your worksheet.

Last Edited by alioth at 09 Jan 11:08
Andreas IOM

A fuel totalizer is pretty redundant and useless on modern engines with EFI and/or with a return line. Fuel is “measured” or meetered directly by the injectors, very precisely, and logged as part of all other engine parameters.


Many of us are still puttering around with an O-320-B3B though :-)

Andreas IOM

LeSving wrote:

A fuel totalizer is pretty redundant and useless on modern engines with EFI and/or with a return line.

Please explain why a fuel totaliser is “pretty redundant and useless”.

ESKC (Uppsala/Sundbro), Sweden
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