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The term Line/Base Trainer is a company name, and the definition can vary between different airlines. The official CAA qualifications are;
TRI (Sim)
Can carry out type rating instruction on the simulator.
TRI (Aircraft and Sim)
Can carry out type rating instruction on the simulator and on the aircraft (base or initial ZFT route flying)
TRE (Sim)
Can carry out type rating skill tests in the simulator.
TRE (Aircraft and Sim)
Can carry out type rating skill tests in the aircraft or the simulator.
RETRE
Company employed TRE who can carry out TRE renewals on behalf of the CAA.
The company can also appoint trainers to carry out certain types of route training which does not include initial ZFT training. These pilots have to undergo a course which is approved by the CAA, but they do not hold a formal CAA qualification.
All TREs must also be TRIs, but you can be a TRI without being a TRE.
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