GM 21.A.435(a) Classification of repairs
ED
Decision 2012/020/R
1. Clarification of the terms Major/Minor
In line with the definitions given in 21.A.91, a new repair is classified as
'major' if the result on the approved type design has an appreciable effect on
structural performance, weight, balance, systems, operational characteristics
or other characteristics affecting the airworthiness of the product, part or
appliance. In particular, a repair is classified as major if it needs
extensive static, fatigue and damage tolerance strength justification and/or
testing in its own right, or if it needs methods, techniques or practices that
are unusual (i.e., unusual material selection, heat treatment, material
processes, jigging diagrams, etc.)
Repairs
that require a re-assessment and re-evaluation of the original certification
substantiation data to ensure that the aircraft still complies with all the
relevant requirements, are to be considered as major repairs.
Repairs
whose effects are considered minor and require minimal or no assessment of the
original certification substantiation data to ensure that the aircraft still
complies with all the relevant requirements, are to be considered ‘minor’.
It is
understood that not all the certification substantiation data will be
available to those persons/organisations classifying repairs. A qualitative
judgement of the effects of the repair will therefore be acceptable for the
initial classification. The subsequent review of the design of the repair may
lead to it being re-classified, owing to early judgements being no longer
valid.
2. Airworthiness concerns for Major/Minor
classification
The
following should be considered for the significance of their effect when
classifying repairs. Should the effect be considered to be significant then
the repair should be classified 'Major'. The repair may be classified as
'Minor' where the effect is known to be without appreciable consequence.
i) Structural performance
Structural
performance of the product includes static strength, fatigue, damage
tolerance, flutter and stiffness characteristics. Repairs to any element of
the structure should be assessed for their effect upon the structural
performance.
ii) Weight and balance
The weight of the repair may have a
greater effect upon smaller aircraft as opposed to larger aircraft. The
effects to be considered are related to overall aircraft centre of gravity and
aircraft load distribution. Control surfaces are particularly sensitive to the
changes due to the effect upon the stiffness, mass distribution and surface
profile which may have an effect upon flutter characteristics and
controllability.
iii) Systems
Repairs to any elements of a system
should be assessed for the effect intended on the operation of the complete
system and for the effect on system redundancy. The consequence of a
structural repair on an adjacent or remote system should also be considered as
above, (for example: airframe repair in area of a static port).
iv) Operational characteristics
Changes
may include:
—
stall characteristics
—
handling
—
performance and drag
—
vibration
v) Other characteristics
—
changes to load path and load
sharing
—
change to noise and emissions
—
fire protection / resistance
Note: Considerations for classifying repairs
'Major/Minor' should not be limited to those listed above.
3. Examples of 'Major' repairs
i) A repair that requires a permanent
additional inspection to the approved maintenance programme, necessary to
ensure the continued airworthiness of the product. Temporary repairs for which
specific inspections are required prior to installation of a permanent repair
do not necessarily need to be classified as 'Major'. Also, inspections and
changes to inspection frequencies not required as part of the approval to
ensure continued airworthiness do not cause classification as 'Major' of the
associated repair.
ii) A repair to life limited or critical
parts.
iii) A repair that introduces a change to the
Aircraft Flight Manual.