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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 that require individual type ratings, meaning you need a specific endorsement for each aircraft type such as the Boeing 737 or Airbus A320. Group 2 covers non-complex motor-powered aeroplanes and is further divided into subgroups based on engine type (turbine or piston) and construction type.
Group 3 covers non-complex motor-powered helicopters with similar subgrouping. For Group 2 and Group 3 aircraft, a full group rating 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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