NOTE: On May 18, 2022, an update of rule 21.A.307 came into force. I have not yet sorted out exactly what effect that update has on the use of parts without a Form 1, but it appears to make it more difficult.
It is generally believed that on certified aircraft you can only use parts that come with an EASA Form 1. (Except standard parts like nuts and bolts.) The EASA Form 1 is a certificate issued by an approved manufacturing or maintenance organisation.
Such a requirement would prevent installation of e.g. used avionics or instruments unless they have been tested or overhauled by an approved maintenance organisation. It would also lead to problems and extra costs when used parts are bought from the USA as the corresponding FAA Form (8130-3) is only valid in Europe for new parts. (Unless it is a “dual release” form which is unusual.)
Fortunately, but little known, this requirement does not necessarily apply to ELA1 or ELA2 aircraft. These categories include non-complex airplanes with a MTOM of at most 2000 kg. “Complex” is used here in the EASA sense of the word which is very different from the more well-known USA FAA usage. Essentially every airplane with a MTOM of at most 2000 kg is non-complex unless it has a jet engine!
The relevant part of the aircraft maintenance rules is ML.A.501 which states that
Unless otherwise specified in Subpart F of Annex I (Part-M), Annex II (Part-145), Annex Vd (Part-CAO) to this Regulation and Annex I (Part-21) to Regulation (EU) No 748/2012, component may be fitted only if all of the following conditions are met: it … has been appropriately released to service using an EASA Form 1 as set out in Appendix II of Annex I (Part-M), or equivalent…
The key passage here is “unless otherwise specified”. In part-21, rule 21.A.307 states:
21.A.307 Release of parts and appliances for installation
A part or appliance shall be eligible for installation in a type-certificated product when it is in a condition for safe operation, and it is:
(a) accompanied by an authorised release certificate (EASA Form 1), certifying that the item was manufactured in conformity to approved design data and is marked in accordance with Subpart Q; or
(b) a standard part; or
(c) in the case of ELA1 or ELA2 aircraft, a part or appliance that is:
(1) not life-limited, nor part of the primary structure, nor part of the flight controls;
(2) manufactured in conformity to applicable design;
(3) marked in accordance with Subpart Q;
(4) identified for installation in the specific aircraft;
(5) to be installed in an aircraft for which the owner has verified compliance with the conditions 1 through 4 and has accepted responsibility for this compliance
So according to sub-paragraph (c) an EASA Form 1 is not needed for “parts” as long as certain requirements are met. (The requirement for an EASA Form 1 does apply to complete aircraft engines and propellers as they are considered to be “products” rather than “parts”.) Let’s go through the requirements in turn.
(1) not life-limited, nor part of the primary structure, nor part of the flight controls;
Straightforward enough. The “primary structure” are the parts of the aircraft that carries flight or ground loads and which would reduce the structural integrity of the aircraft if they fail. So you can’t install a used wing spar or rudder cable unless it has an EASA Form 1, but a COM radio would be ok.
(2) manufactured in conformity to applicable design;
Basically this means that the part is designed for its intended purpose and not “counterfeit”. It is very unlikely that something that looks like a COM radio made by a well-known manufacturer would actually be something else. It would be more complicated with a more nondescript part.
Sometimes the conformity can be diffiult to determine. E.g. an aircraft manufacturer could have used an off the shelf part (e.g. a pump or switch) designed and manufactured by someone else but given it their own part number. In that case it is ok to buy a replacement part off the shelf from the manufacturer or its dealers, but you have to make certain that the pump or switch you buy is identical to what the aircraft manufacturer bought. Another case is when a part which is taken from an aircraft to be installed on another aircraft of the same model but which was manufactured in a different year. The part may have a slightly different design and thus be unsuitable.
(3) marked in accordance with Subpart Q;
Subpart Q requires (rule 21.A.804) that the part be marked with the manufacturer’s name, trademark or symbol and part number. ETSO authorised parts (e.g. avionics) should be marked with additional information according to rule 21.A.807. This is standard procedure and should not pose a problem. (Unless, of course, the markings have been removed!)
If it is impractical to have the information on the part itself (e.g. due to its size), it can be given on the packaging of the part.
(4) identified for installation in the specific aircraft;
This simply means that the owner of the aircraft declares that the particular part be installed in the aircraft.
(5) to be installed in an aircraft for which the owner has verified compliance with the conditions 1 through 4 and has accepted responsibility for this compliance
So in the end it is the responsibility of the owner to determine if it is appropriate to use the part. Recall that 21.A.307 also states that the part must be in a “condition for safe operation”. That decision would be based on inspection of the part, knowledge of the part’s history and how critical the part is for the operation of the aircraft. The mechanic installing the part will probably want you to sign in the aircraft records that you’ve accepted this responsibility.
If you remove the part from an aircraft in working condition for the purpose of installing it in another aircraft then you probably wouldn’t hesitate. Also not if the part has an FAA Form 8130-3. (Really, if it is good enough for an aircraft in the USA, it should be good enough for an aircraft in Europe!)
Some final notes:
EASA has written a memorandum about using parts without an EASA Form 1 which you should read if you plan to make use of this possibility. You could also show this memorandum to a shop or mechanic who is hesitant to accept a part provided under these provisions.
If the installation of the part involves a modification of the aircraft – that is if you make a new installation as opposed to replacing a broken existing part with an equivalent part – then you will also need approval for the installation itself. In many cases this can be covered by a “Standard Change”, or you may need an STC or a modification approval from EASA. In any case, that is unrelated to whether the part itself comes with an EASA Form 1 or not.