Airwothiness Notices - B045, Edition 1 - 15 May 1998
Compatibility of Multiple Modifications
Purpose
The purpose of this notice is to
remind aircraft owners, operators and maintainers of the requirements to ensure
compatibility of the latest modification being installed with other
modifications previously installed on the given aircraft.
Note: Although this issue predominantly applies
to modifications, it could also apply to repairs in specific cases.
Regulatory Requirements
Federal Aviation Administration (FAA) and Transport Canada supplemental type certificates normally include a
compatibility statement which states in part:
“Conditions: Prior to incorporating this modification, the installer
shall establish that the interrelationship between this change and any other
modifications(s) incorporated will not adversely affect the Airworthiness of the
modified product.”
The compatibility requirements
specified above equally apply to a modification for which its installation was
approved under an FAA 337 Field Approval, or another form of approval acceptable
to the Minister.
Examples
The following, although not an all
inclusive list, provides examples of types of modifications or a combination
thereof which could introduce some incompatibility, e.g. the installation of:
- Autopilots on aircraft fitted with lift devices or other changes which
affect the flight characteristics of the aircraft, i.e. a combination of
modifications which individually increase the drag of the aircraft.
- Satellite communications equipment and global positioning system (GPS)
navigation equipment, i.e. avionics equipment which may have adverse
interaction.
- Engine, propeller and airframe modifications which have not been
specifically approved together.
- Several accessories mounted on the skid tubes of helicopters.
- Modifications which introduce new operating limitations or procedures
that are contrary to those limitations or procedures specified in other flight
manual supplements.
- Modifications which include several structural design changes and which
may cause superposition of stresses, reduction in stiffness or changes to fail
safe or damage tolerance characteristics.
Installer’s Responsibilities
Persons involved with the
installation of a latest modification should assess its functional and
operational compatibility with other modifications already installed, and ensure
that it will not introduce any adverse characteristics, such as physical
interference or impact on the operation of other modifications installed.
Where the assessment required to ensure compatibility between all
modifications installed exceeds the installer’s capability, he/she should then
enlist necessary engineering support to make that determination.
Where adverse interrelationship is evident, negotiations should be
undertaken with the approval holder or a qualified person, e.g. a delegate, to
resolve the unsatisfactory situation.
Where operating limitations
inherent to specific modifications are conflicting, the most restrictive
limitations shall be applied. In
some cases, the development of a new flight manual supplement may be required to
prescribe the operating envelope applicable to the multi-modification configured
aircraft.
A compatibility assessment of
installed modifications should also be repeated whenever an aircraft is
converted for operation in a different role or when a change in its basic
configuration has occurred, e.g. changing from: 1) cargo to a
passenger configuration, 2) landplane
to seaplane configuration, 3) normal utility to restricted category, etc.
Statement of Compatibility
In addition to meeting the
objectives set forth in a Conformity Certificate - Repair or Modification,
24-0045 form, the inclusion of a statement of compatibility by the installer
would provide interested parties with assurance that compatibility of the latest
modification with other modifications previously installed has been assessed and
proven satisfactory.
For Minister of Transport
K.J. Mansfield
Director, Aircraft Certification
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