AERO 417 – STANDARDS/RULES/CERTIFICATION OF AEROSPACE
POST-MIDTERM REVIEW PACKAGE (LECTURES 6-9) CONCORDIA
UNIVERSITY
Lecture 6 – Repair and Modifications
Design changes can be classified under 2 different definitions:
o Repair: Restores the aircraft to an airworthy condition
“Airworthy” in respect of an aircraft or aeronautical product means
fit, safe and inconformity to applicable standards or airworthiness
(ie. AWM)
o Modification: Enhances utility of aircraft. Must also continue to be air
worthy after modifications have been made, like repairs. When a
modification is made, it requires adesign change approval. The reasons
being:
I. Legally required; no person shall operate an aircraft in flight unless
flight authority (certificate of airworthiness…attesting to an
aircraft’s fitness for flight)is in effect in respect of the aircraft. The
Minister shall issue a C of A if
a. Which an aircraft has a type certificate
b. That conforms to its certified type design
c. Is safe for flight
II. Safety: Incorporating design change means the aircraft is no longer
conforming toits type design. The modification has to be reviewed
against the basis of certification it was certified to. Requires a
compliance reporting process (The Compliance Program).
III. Financially: When a modification is made, insurance becomes invalid
if a C of Ais not in force, which can result in fines and loss of revenue.
Design change approval is separated in to two categories: MAJOR and MINOR
o MAJOR modifications as listed in the AWM 571.06 mean an
,alteration that in theopinion of the Minister, has significant effects
on
Operational Limits (ie: gross weight, center of gravity, AFM changes,
stall speed)
Structural Strength
Performance, both degraded or enhanced
Power Plant Operation
Flight Characteristics
or any other characteristics directly affecting airworthiness.
, o MINOR modifications as listed in the AWM 571.06 is anything that has no
appreciable effect on the weight, balance, structural strength, reliability, or
operational characteristicsaffecting the airworthiness of the product,
which would otherwise be listed as MAJOR (14 CFR 21.93(a) Classification
of Changes in Type Design)
The following is a list of the “Critical Five” which are the five critical elements
involved withcontinuing airworthiness:
1. Weight: Is there an increase or decrease to the weight limitations? (ie:
minimum flyingweight, minimum fuel weight, landing weight, take-off
weight).
2. Balance: Is there an increase or decrease in the CG limitations?
(including maximumforward, and aft limits, or the shape of a variation
between weights).
3. Structural Strength: Is there a change to the product strength, either
by a materialchange, a geometry change or a change in the load
magnitude of path
4. Reliability: Is there a change in the failure mode, lifetime or ability of
the product tomeet its intended function.
5. Operational Characteristics: Is there a change to performance, stability
and control,take-off and landing, or handling of the aircraft, stall and
speed characteristics.
The approval process for a modification and/or repair is similar to that of initial
certification except on a smaller scale. The exercise is to demonstrate that the
modification or repair conformsto the original certification basis.
The “Changed Product Rule” came into effect on June 10, 2003.
o Must comply with the regulations in effect on the date of application
for the change,rather than those regulations incorporated by
reference in the type certificate.
Regulation: CAR Part V,
Subpart 21
, Design Change Division for Approval
Changes to a Type Design Division IV
Supplemental Type Certificates Division V
Repair Design Approvals Division VI
Standard: AWM 513
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