Ratings and further training
Differences training has two different uses within the licensing system.
The first use is to train the pilot for flight in more complex aircraft than the pilot has flown before within a class rating already held.
When a licence and rating combination, for example a PPL(A) with SEP(Land) rating is initially gained, the training has usually been in aircraft with simple systems or features, for example, in an aircraft with a fixed (rather than retractable) undercarriage, and with a fixed pitch propeller rather than one with variable pitch.
The resulting rating, in this case SEP(Land), would be valid in all aircraft in that class (subject to familiarisation with the aircraft itself), providing the new aircraft has similar simple systems and features. However, to move to an aircraft within the SEP(Land) class which has more complexity, the pilot would need formal differences training and log book sign-off from a suitable instructor before making the first flight as pilot in command in any aircraft with the complexity. The content of the training should only be concerned with operations with the specific complexity.
The following list of features require further differences training before first flight as pilot in command. The list varies slightly for holders of an SEP rating (or privileges within the LAPL) compared to an NPPL SSEA rating.
The second use of differences training is a more general concept used to extend the privileges of an existing licence, privilege or rating on a national basis.
For example, EASA FCL does not itself provide for a pilot with a LAPL(A) with SEP privileges (or a PPL(A) with SEP rating) to fly a microlight aircraft, but neither does it object to national authorities extending the use of that licence on a national basis to non-EASA aircraft (such as a microlight) through national legislation. The UK has legislated to allow pilots qualified for SEP(land) aircraft to fly G registered microlight aircraft in the UK, providing the pilot undergoes differences training for microlight aircraft, and has this training signed-off in their personal log book by a suitably qualified instructor. In this context, Differences Training is used to permit flight of a category of aircraft rather than simply a feature within an aircraft.
For pilots with SEP or TMG privileges, differences training once completed does not have to be repeated. But pilots who have not flown using the particular 'difference' for some time are recommended to assess their flying experience and take appropriate training that they feel necessary even if it is not legally compulsory.