Conversions
Conversions can be easy or take time depending on the governing Aviation Authority. Some countries and regions may require only a few documents to be filled out and processed by the national autority. The european EASA makes the process more difficult to convert your license. EASA lays out guidelines and rules for the national CAAs and only has an agreement in place with the FAA to convert a Private Pilot License.
The following is an excerpt from the swedish Civil Aviation Authority "transportstyrelsen" about PPL conversions to EASA
This handbook strives to streamline and clarify when a conversion can be executed based on the BASA treaty, Annex 3. Our explanation finds its roots in a document that comprises both the appeal and the skill exam for the issuance of PPL, SEP, MEP, as well as nocturnal and/or instrumental ratings grounded on the related FAA certificate and ratings corresponding to the BASA treaty. We aim to make the conversion of certificates and/or ratings from FAA to EASA simpler as demonstrated in the following table.
Note that an IR(A) based on BASA Annex 3 can only be issued together with or for a PPL(A). If an applicant wishes to use their IR(A) together with a higher certificate, such as a CPL, in addition to the experience requirements in Part-FCL, a complete theoretical examination in accordance with FCL.025 and FCL.615 IR is required. Please note that according to BASA agreement Annex 3, it is not possible to convert individual ratings to a higher licence than PPL(A).
Nothing prevents a holder of a PPL(A) converted in accordance with BASA agreement Annex 3 from pursuing a higher licence, such as CPL(A) through further training in accordance with Part-FCL. However, a holder of an EASA CPL(A) cannot convert ratings according to the BASA agreement and must instead follow Article 10 of the delegated regulation (EU) 2020/723.
If you want to obtain a EASA CPL, you will have to convert your License by attending a long theory course (unless you hold an ICAO ATP), take the same Theory exams for ATPL or CPL as all other EASA flight students and then do a flight training course with the approval of a national CAA. The whole conversion can take between 6-12 months and realistically takes in average 8-10 months full time and will cost around 15000 Euros for a CPL ME-IR Conversion.
Basically there are two ways to start this. If you hold a FAA license, you can convert your PPL with by completing a Checkride and then do the Theory Exams and finish with training and a Checkride for the CPL.
Or more efficiently, you can directly take the ATPL or CPL Exams as you can sign up at an ATO that offers the required theory classes (distance or class learning) with an ICAO PPL.
How to convert your ICAO CPL to an EASA CPL with ATPL theory credit.
Alternatively: Validation
If you just want to fly in Europe for a short period of time and hold a FAA license, you can get a validation by a CAA for a period of 30 days within 180 days of the year. This rule has just recently been adapted by CAAs and will allow you to only fly specific planes, as you will have to choose tailnumbers that your validation will be linked to.