How are evolution and variants of aircraft considered by certification authorities?

Question

Recently, both Boeing and Airbus launched "new" aircraft as a modernized version of their respective best sellers (B737MAX and A320neo). To narrow the question down, I will consider the A320 and the FAA, but the same goes for the B737 and almost certainly many more aircraft families, and I hope for other certification authorities as well. I'm not really clear on the difference between type, model and series but I think the difference may be relevant for the certification process. Perhaps highlighting this difference is enough to answer the question.

Wikipedia lists multiple variants of the A318. Do the A318-111 and the A318-121 require different certifications?

Moreover, when adding a variant to the family (here adding the A318 to the family composed of the A319, the A320, and the A321), do the certification authorities consider this aircraft as a totally new one or only as a variant of existing one (many shared components)? Can this consideration lighten the certification process?

Is the new version (A320neo) considered as a new aircraft by the certification authority and does it thus require the same set of tests as a new aircraft?

In short, when a new aircraft is an evolution or a variant of a previous one, how is it considered by certification authorities?

Answer 1

Variants are seen as a modification of an existing airplane design, and only the changed parts need to be certified. The real advantage is that the set of rules the certification has to comply with are frozen at the time of the initial application, so any additional rules that had been added later are not relevant. This is called "grandfather rules".

This definitely lightens the certification process and makes it less complex, but makes the safety enhancements, which were added after the type was certified first, optional for newly built airplanes.

The A318, A319 and A321 are all variants of the original A320, and the subtypes you name differ in their engine. Each engine option has to be certified separately, but all certification work not related to the engine can be shared between the variants. Additionally, the purchaser will select his options for instrumentation and furnishing, chosen from a limited set of previously certified options.

When a new version is introduced, the public will get a very different message from the airplane maker than the certification authorities. For the PR, the new variant is all new, but the FAA and the EASA will hear that almost nothing changed. In the end, it is similar to corporate profits: The shareholders get told the company made oodles of money, while the tax authorities will be presented with a bleak picture of mainly losses.

Answer 2

I'm not really clear on the difference between type, model and series

A type is the basic airplane design, like the A320 type, which includes the A318, A319, A320, and A321. A series is the basic version of the type, like the A320-100 series. A model is the specific configuration of the series, like the A320-111 model. The model may be mainly a different engine, or also include other changes specific to a customer.

Do the A318-111 and the A318-121 require different certifications?

No. Airplanes are generally certified at the type level, which also covers all series and models of that type. However, each new model does have to be certified, which means it must be included in the applicable type certificate.

When adding a variant to the family, does the certification authority consider this aricraft as a totally new one or only as a variant of existing one?

As above, a new variant will generally be considered a new series within that family (type), and so will be included in the applicable type certificate.

Is the new versions (A320neo) considered as a new aircraft by the certification authority and thus require the same set of test as a new aircraft?

As with new variants, new versions like the A320neo are usually included in the same type certificate, but this can vary between authorities. For example, it looks like the UK's CAA has separate type certificates for the 747-100/200 (FA5) and the 747-400 series (FA44). The FAA (A20WE) and EASA (EASA.IM.A.196) have one certificate for the whole 747 series.

The level of work required to certify a new model or series depends on the degree of differences from the previously certified configurations. If something was previously certified, then this will probably apply on the new model. Of course there will be more differences for a new type than just a series, especially when changing other aspects of the design, as with the A320neo. The decisions on what needs additional work to certify are specific to each situation.

As others have mentioned, there are multiple certifiying authorities around the world. An aircraft is first certified with the authority in the country of manufacture (EASA in Europe, FAA in the US, CTA in Brazil, etc.). When an aircraft is to be operated in another country, to avoid restrictions on operation, the authority in that country must also certify the aircraft. The authorities tend to have agreements with each other to make this process easier.

Answer 3

First of all, the Certification Authority for Airbus is EASA, for Boeing it is the FAA.

Let's look at the A320 family. All variants, A318, A319, A320 and A321 of all series are on the same type certificate EASA A.064(data sheet). For the areas where these aircraft are different from the original A320, Airbus has demonstrated that they meet the requirements specified in the regulations. The A320neo will treated the as a new variant of the A320, so only the differences are tested for. Note that this is by no means a small task if you are introducing a number of significant changes which affect the performance of the aircraft.

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The Boeing 737 type certificate is FAA.A16WE (datasheet).