Page 266 - The Jet Engine

Maintenance

26. The progressive introduction of improved and
more reliable condition monitoring devices (para. 11)
will have considerable influence on accepted trouble
shooting practice, since to a large extent these
devices are designed to pin-point, at an early stage,
the specific system or assembly at fault. The
development of suitable test sets could eventually
eliminate the need for engine ground testing after
trouble shooting

ADJUSTMENTS

27. There are usually some adjustments that can be
made to the engine controlling the fuel trimming
devices. Typical functions for which adjustment
provision is normally made include idling and
maximum r.p.m., acceleration and deceleration
times, and compressor air bleed valve operation.
28. Adjustment of an engine should be made only if
it is quite certain that no other fault exists that could
be responsible for the particular condition, The
maintenance manual instructions relative to the
adjustment must be closely adhered to at all times. In
many instances, subject to local instructions, a
ground adjustment can be made with the engine Fig. 24-5 Typical friction locked adjusters.
running.

29. Adjusters are usually designed with some form
of friction locking (fig. 24-5) that dispenses with
locknuts, lockplates and locking wire. On some and is usually only carried out after engine installa-
engines, provision is also made for fitting remote tions, during trouble shooting, or to test an aircraft
adjustment equipment (fig. 24-6) that permits system. With the improved maintenance methods
adjustment to be made during ground test with the and introduction of system test sets which simulate
cowls closed, the adjustment usually being made running conditions during the checking of a static
from the flight deck. engine, the need for ground testing, particularly at
high power, is becoming virtually unnecessary.

32. Before a ground test is made, certain
GROUND TESTING precautions and procedures must be observed to
prevent damage to the engine or aircraft and injury to
30. The basic purpose of engine ground testing is to
confirm performance and mechanical integrity and to personnel.
check a fault or prove a rectification during trouble 33. Because of the mass of air that will be drawn
shooting. Ground testing is essential after engine into the intake and the resultant high velocity and
installation, but scheduled ground testing may not
normally be called for where satisfactory operation temperature of the exhaust gases during a ground
test, danger zones exist at the front and rear of the
on the last flight is considered to be the authority or
acceptance for the subsequent flight. In some aircraft. These zones will extend for a considerable
instances, this is backed up by specific checks made distance, and atypical example is shown in fig. 24-7.
in cruise or on approach and, of course, by evidence The jet efflux must be clear o! buildings and other
from flight deck indicators and recordings. aircraft. Personnel engaged in ground testing must
ensure that any easily detachable clothing is
31. For economic reasons and because of the securely fastened and should wear acoustic ear
noise problem, ground testing is kept to a minimum muffs.

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