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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
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
engines, provision is also made for fitting remote
adjustment equipment (fig. 24-6) that permits
adjustment to be made during ground test with the
cowls closed, the adjustment usually being made
from the flight deck.
GROUND TESTING
30. The basic purpose of engine ground testing is to
confirm performance and mechanical integrity and to
check a fault or prove a rectification during trouble
shooting. Ground testing is essential after engine
installation, but scheduled ground testing may not
normally be called for where satisfactory operation
on the last flight is considered to be the authority or
acceptance for the subsequent flight. In some
instances, this is backed up by specific checks made
in cruise or on approach and, of course, by evidence
from flight deck indicators and recordings.
31. For economic reasons and because of the
noise problem, ground testing is kept to a minimum
and is usually only carried out after engine installations,
during trouble shooting, or to test an aircraft
system. With the improved maintenance methods
and introduction of system test sets which simulate
running conditions during the checking of a static
engine, the need for ground testing, particularly at
high power, is becoming virtually unnecessary.
32. Before a ground test is made, certain
precautions and procedures must be observed to
prevent damage to the engine or aircraft and injury to
personnel.
33. Because of the mass of air that will be drawn
into the intake and the resultant high velocity and
temperature of the exhaust gases during a ground
test, danger zones exist at the front and rear of the
aircraft. These zones will extend for a considerable
distance, and atypical example is shown in fig. 24-7.
The jet efflux must be clear o! buildings and other
aircraft. Personnel engaged in ground testing must
ensure that any easily detachable clothing is
securely fastened and should wear acoustic ear
muffs.
Maintenance
256
Fig. 24-5 Typical friction locked adjusters.
Maintenance
257
Fig. 24-6 Remote adjustment equipment fitted to a turbo-propeller engine.
34. The aircraft should be headed into wind and
positioned so that the air intake and exhaust are over
firm concrete, or a prepared area that is free from
loose material and loose objects, and clear of
equipment. Where noise suppression installations
are used, the aircraft should be positioned in
accordance with local instructions. When vertical
take-off aircraft are being tested, protective steel
plates and deflectors may be used to prevent ground
erosion and engine ingestion of exhaust gases and
debris. Aircraft wheels should be securely chocked
and braked; with vertical take-off aircraft, anchoring
Maintenance
258
Fig. 24-7 Ground running danger zones.
or restraining devices are also used. Adequate fire
fighting equipment must be readily available and
local fire regulations must be strictly enforced.
35. Before an engine is started, the air intake and
jet pipe must be inspected to ensure that they are
free from any debris or obstruction. Each operator
will detail his individual pre-start inspection requirements;
a typical example of this for a multi-engined
aircraft is shown in fig. 24-8.
36. The starting drill varies between different
aircraft types and a starting check procedure is
normally used. Generally, all non-essential systems
are switched or selected off; warning and emergency
systems are checked when applicable. Finally, after
ensuring that the low pressure fuel supply is selected
on, the starting cycle is initiated.
37. At a predetermined point during the starting
cycle, the high pressure fuel shut-off valve (cock) is
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