EA, et al.
The words from LASORS Section E wrt converting an ICAO IR to JAA IR (or adding a JAA IR to a JAA/CAA PPL/CPL using the ICAO IR as a basis)
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1. Complete a minimum of 15 hours instrument time under instruction, of which 5 hours may be in a FNPT 1 or 10 hours in a FNPT 2 or Flight Simulator.
2. Additional IR training considered necessary by the Head of Training of an approved FTO.
3. Pass a 170A Flight Test.
4. Pass the JAR IR(A) Skill Test.
5. Pass the JAR IR(A) or ATPL(A) Theoretical Knowledge examinations as appropriate.
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Point 2 above may be the gotcha for anyone thinking it is a piece of piss to do it FAA --> JAA.
Also worth remembering that the 170A is going to take about 2 hours, as is the IRT...
LASORS Section E
Edited to add link to LASORS-E