Page 264 - The Jet Engine

Maintenance

21. Before an inspection of the air intake or exhaust
system is made it must be ascertained that there Is
no possibility of the starter system being operated or
the ignition system being energized.

22. A final inspection of the engine, air intake and
exhaust system, must always be made after any
repair, adjustment or component change, to ensure
that no loose items, no matter how small, have been
left inside. Unless specific local instructions rule
otherwise, air intake and exhaust blanks or covers
should be fitted when engines are not running.
TROUBLE SHOOTING

23. The procedure for locating a fault is commonly
referred to as trouble shooting, and the requirement
under this procedure is for quick and accurate
diagnosis with the minimum associated work and the
prevention of unnecessary unit or engine removals.
Fig. 24-2 Inspection of H.P. nozzle guide 24. The basic principle of effective trouble shooting
vanes.
is to clearly define and interpret the reported
and magnetic chip detector history and catalogue the symptom and then proceed to a logical and
yield of particles. Fuel filters may incorporate a silver systematic method of diagnosis (fig. 24-3).
strip indicator that detects any abnormal concentra-
tion of sulphur in the fuel.
MAINTENANCE PRECAUTIONS
19. During engine maintenance, it is necessary to
observe certain precautions. The ignition system is
potentially lethal and, therefore, before any work is
done on the high energy ignition units, igniter plugs
or harness, the low tension supply to the units must
be disconnected and at least one minute allowed to
elapse before disconnecting the high tension lead.
Similarly, before carrying out work on units
connected to the electrical system, the system must
be made safe, either by switching off power or by
tripping and tagging appropriate circuit breakers.
With some installations, the isolation of certain
associated systems may be required.

20. When the oil system is being replenished, care
must be taken that no oil is spilt. If any oil is acciden-
tally spilt, it should be cleaned off immediately as it is
injurious to paintwork and to certain rubber
compounds such as could be found in the electrical
harnesses, Oil can also be toxic through absorption
if allowed to come into contact with the human skin
for prolonged periods. Care should be taken not to
overfill the oil system; this may easily occur if the
aircraft is not on level ground or if the engine has
been stationary for a long period before the oil level Fig. 24-3 Trouble shooting - logical
is checked. sequence.

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