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 installa-tions, 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
Maintenance
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
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 require-ments; 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 opened to allow fuel to pass to the fuel spray nozzles, this point varying with aircraft and engine type; on some installations the shut-off valve may be opened before the starting cycle is initiated. During the engine light-up period and subsequent accelera-tion to idling speed, the engine exhaust gas temperature must be carefully monitored to ensure
Maintenance
that the maximum temperature limitation is not exceeded. If the temperature limitation appears likely to be exceeded, the shut-off valve must be closed and the starting cycle cancelled; the cause and possible effect of the high temperature must then be investigated before the engine is again started.
38. When a turbo-propeller engine is being started, the propeller must be set to the correct starting pitch, as recommended by the engine manufacturer. To provide the minimum resistance to turning and thus prevent an excessive exhaust gas temperature occurring during the starting cycle, some propellers have a special fine pitch setting.
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