4.4.1 These are engines used primarily for main
propulsion. They normally require adjustment or modification to suit
the on-board operating conditions but which should not result in NOx emissions exceeding the limits in 3.1 of
this Code.
4.4.2 The engine group concept also provides the
possibility for a reduction in approval testing for modifications
to engines in production or in service.
4.4.3 In general, the engine group concept may
be applied to any engine type having the same design features as specified
in 4.4.5, but individual engine adjustment or modification after test-bed
measurement is allowed. The range of engines in an engine group and
choice of parent engine shall be agreed to and approved by the Administration.
4.4.4 The application for the engine group concept,
if requested by the engine manufacturer or another party, shall be
considered for certification approval by the Administration. If the
engine owner, with or without technical support from the engine manufacturer,
decides to perform modifications on a number of similar engines in
the owner's fleet, the owner may apply for an engine group certification.
The engine group may include a test engine on the test bench. Typical
applications are similar modifications of similar engines in service
or similar engines in similar operational conditions.