Maintenance
5.
Because the T.B.O. is actually determined by the life of one or two assemblies within the engine, during overhaul, it is generally found that the other assemblies are mechanically sound and fit to continue in service for a much longer period. Therefore, with the introduction of modular engines and the improved inspection and monitoring techniques available, the T.B.O. method on limiting the engine's life on-wing has been replaced by the 'on-condition' method.
6.
Basically this means that a life is not declared for the total engine but only for certain parts of the engine. On reaching their life limit, these parts are replaced and the engine continues in service, the remainder of the engine being overhauled 'on condition', Modular constructed engines are particularly suited to this method, as the module containing a life limited part can be replaced by a similar module and the engine returned to service with minimum delay, The module is then disassembled for life limited part replacement, repair or complete overhaul as required.
ON-WING MAINTENANCE
7. On-wing maintenance falls into two basic categories: scheduled maintenance and unscheduled maintenance.
Scheduled maintenance
8.
Scheduled maintenance embraces the periodic and recurring checks that have to be effected in accordance with the engine section of the appropriate aircraft maintenance schedule. These checks range from transit items, which do not normally entail opening cowls, to more elaborate checks within specified time limits, usually calculated in aircraft flying hours and phased with the aircraft check cycle.
9.
Continuous 'not-exceed-limit' maintenance, whereby checks are carried out progressively and as convenient within given time limits rather than at specific aircraft check periods, has been widely adopted to supersede the check cycle. With the progressive introduction of condition monitoring devices (para. 11) of increased efficiency and reliability, a number of traditionally accepted scheduled checks may become unnecessary. Extracts from a typical maintenance schedule are shown in fig. 24-1.
Unscheduled maintenance
10. Unscheduled maintenance covers work neces-sitated by occurrences that are not normally related to time limits, e.g. bird ingestion, a strike by lightning, a crash or heavy landing, Unscheduled work required may also result from malfunction, trouble shooting, scheduled maintenance, and occasionally, manufacturers' specific recommendations. This type of maintenance usually involves rectification adjustment or replacement.
CONDITION MONITORING
11. Condition monitoring devices must give indication of any engine deterioration at the earliest possible stage and also enable the area or module in which deterioration is occurring to be identified. This facilitates quick diagnosis, which can be followed by scheduled monitoring and subsequent programmed rectification at major bases, thereby avoiding in-flight shut-down, with resultant aircraft delay, and minimizing secondary damage. Monitoring devices and facilities can be broadly categorized as flight deck indicators, in-flight recorders and ground indicators.
Flight deck indicators
12. Flight deck indicators are used to monitor engine parameters such as thrust or power, r.p.m., turbine gas temperature, oil pressure and vibration. Most of the indicators used are described in Part 12. Other devices, however, may be used and these include:
Accelerometers for more reliable and precise
vibration monitoring.
Radiation pyrometers for direct measurement of
turbine blade temperature.
Return oil temperature indicators.
Remote indicators for oil tank content.
Engine surge or stall detectors.
Rub indicators to sense eccentric running of
rotating assemblies.
In-flight recorders
13.
Selected engine parameters are recorded, either manually or automatically, during flight. The recordings are processed and analyzed for significant trends indicative of the commencement of failure. An in-flight recording device that may be used is the time/temperature cycle recorder. The purpose of this device is to accurately record the engine time spent operating at critical high turbine gas temperatures, thus providing a more realistic measure of 'hot-end' life than that provided by total engine running hours.
14.
Automatic systems (Part 12) known as aircraft integrated data systems (A.I.D.S.) are able to record parameters additional to those normally displayed
e.g. certain pressures, temperatures and flows.
15. Many of the electronic components used in modern control systems have the ability to monitor
Maintenance
their own and associated component operation. Any fault detected is recorded in its built-in memory for subsequent retrieval and rectification by the ground crew. On aircraft that feature electronic engine parameter flight deck displays (Part 12) certain faults are also automatically brought to the flight crew's attention. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：劳斯莱斯喷气引擎－中英(118)
