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66.A.5 defines how aircraft are classified into groups and subgroups for the purpose of type rating endorsements on Part 66 licences.
What it means in practice
Aircraft are organised into groups based on their complexity and characteristics. Group 1 covers complex motor-powered aircraft, multi-engine helicopters, aeroplanes with a maximum certified operating altitude above FL290, aircraft equipped with fly-by-wire systems, gas airships other than ELA2, and any other aircraft requiring an individual type rating when so defined by the Agency — meaning you need a specific endorsement for each aircraft type such as the Boeing 737 or Airbus A320.
Group 2 covers aircraft other than Group 1 in three sub-groups: sub-group 2a — single turboprop-engine aeroplanes (plus those turbojet and multiple-turboprop aeroplanes the Agency classifies here because of their lower complexity); sub-group 2b — single turbine-engine helicopters (plus lower-complexity multiple-turbine helicopters so classified); and sub-group 2c — single piston-engine helicopters (plus lower-complexity multiple-piston helicopters so classified). Group 3 covers piston-engine aeroplanes other than those in Group 1, and Group 4 covers sailplanes, powered sailplanes, balloons, and airships other than those in Group 1. For Group 2, 3, and 4 aircraft, a full group or subgroup rating may be sufficient rather than an individual type rating, which simplifies licensing for engineers who work on multiple similar aircraft types within the same subgroup.
Key requirements
For Group 1 aircraft, each type rating requires completion of an approved type training course and a corresponding examination, along with practical experience on that specific type. There are no shortcuts: each complex aircraft type must be individually endorsed on the licence.
For Group 2 and Group 3 aircraft, the competent authority may endorse a full group or subgroup rating. This allows licence holders to certify maintenance on any aircraft within that group or subgroup, provided they have adequate knowledge and experience. The specific training and examination requirements vary depending on the group and subcategory of the licence held.
Common compliance gaps
A common mistake is assuming that a subgroup rating automatically covers all aircraft within that subgroup without any further familiarisation. While the licence endorsement may cover the subgroup, the approved maintenance organisation still needs to ensure the certifying staff member has adequate knowledge of the specific aircraft type before authorising them. Organisations must maintain their own authorisation process to bridge any gap between the licence endorsement and practical competence on a particular aircraft.
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