OSD

In the OSD Flight Crew (OSD FC) context, familiarisation is the lightest form of training required when a pilot already holds the type rating and needs to operate another variant (or a modified version) of the same aircraft.

Core distinction (EASA rules)

Under FCL.710 (Part-FCL) and ORO.FC.125 (Air Operations):

• Familiarisation requires only the acquisition of additional knowledge.
  No practical skill training on a device or aircraft is mandated.
• Differences training requires additional knowledge + practical training on the aircraft or an appropriate training device.

The OSD FC document for a specific type (e.g. A330/350) defines exactly which transitions need which level through its Master Differences Requirements (MDR) tables and Difference Requirements (DR) tables.

When familiarisation is required

Familiarisation is required when the differences between variants (or between a base aircraft and a modified version) are assessed at the lowest difference levels in the OSD FC:

Practical triggers for familiarisation include:

• Transitioning between variants listed in the same cellof the EASA Class and Type Rating & Licence Endorsement List (no horizontal line separating them).
• Minor system, equipment or procedural changes that the OSD FC evaluates as Level A (or sometimes B).
• Operating another aircraft of the same type when only knowledge updates are needed (AMC1 ORO.FC.125).
• Certain equipment or procedure changes that do not affect handling qualities or require new skills.

How the OSD FC controls it

The OSD FC (approved as part of the Type Certificate) contains:

• The list of variants covered by the single licence endorsement (e.g. A330/350).
• MDR/DR tables that assign the exact difference level (A–E) for every relevant comparison.
• Any Training Areas of Special Emphasis (TASE) that must still be covered even in familiarisation.

Operators must follow these OSD FC provisions. The Operations Manual then specifies exactly when and how the familiarisation is delivered (self-study, briefings, CBT, etc.).

In short:
Within the OSD framework, familiarisation is required for the smallest differences between variants of the same type rating — those that can be safely covered by knowledge alone (primarily Level A, sometimes Level B). Anything that needs practical skill practice becomes formal differences training.