General (ICAO)

ICAO Annex 1 distinguishes class and type ratings. Differences within one class can be bridged by Differences Training without acquiring a new class rating.

Europe (EASA / EU)

Regulation (EU) 1178/2011 Part-FCL.710 (Class and type ratings — variants) defines two levels of conversion within the same class or type rating:

1. Familiarization

Required when a pilot moves between similar variants.
Acquisition: Familiarization with the characteristics of the model/variant may be carried out self-study through the AFM/POH and possibly a cockpit briefing.
No mandatory licence endorsement; the logbook should record the familiarization.

2. Differences Training

Required when a pilot moves between significantly different variants within the same class/type rating.
Mandatorily completed with an instructor (CRI or FI).
Content: theoretical instruction + practical demonstration of the differences.
Logbook entry mandatory, signed by the instructor.
Validity (FCL.710(b)): If Differences Training for a specific variant has not been exercised within the last 2 years, a new Differences Training must be completed — exception: variants previously obtained via the class rating itself.

Common triggers for Differences Training:

Change from carburettor to fuel injection,
Change from fixed-pitch to variable-pitch/constant-speed propeller,
Change from normally aspirated to turbocharged/supercharged engine,
Change to tailwheel/conventional gear,
Change to retractable gear,
Change to EFIS / glass cockpit (e.g. analog to Garmin G1000),
Change to pressurised cabin,
Change to anti-icing / de-icing equipment.

Examples:

C172 → C172RG (retractable gear): Differences Training required.
C172 with analogue cockpit → C172 with G1000: typically Differences Training for EFIS.
C172 → C152: Familiarization (both normally aspirated, fixed-pitch, nose-wheel).
PA-28-140 → PA-28-181: Familiarization (same class rating, similar performance).

Record-keeping (FCL.710(d)): The pilot must carry or have available proof of the completed Differences Training (logbook entry suffices).

Germany (national)

EU law applies directly. AMEs / flight schools clarify with the LBA in case of doubt which variants require which training level. National practice strictly follows FCL.710.