Table of Contents
20. Assembly and Disassembly
In the following assembly and disassembly is understood as a mechanical process or mounting respectively unbuilding or dismounting of aeroengines and their components. To this belongs as well maintenance as also work in (repair) shops. This demands a high degree often specific expert knowledge. To this belongs the understanding of the functions and the coaction of the components. Those activities have a high risk potential.
On the other hand assembly and disassembly provide an important contribution to the safety of aeroengines. The technician comes with the components into a tight and aware contact. This gives the chance that deviations in the outside appearance or an unnormal behaviour during maintenance attracts attention. Such can be a poor pipeline fitting which must be tensioned during the assembly. The tensionings can promote vibration fatigue fractures which means for oil lines and fuel lines a high risk (Ill. 23.5.2-6).
There may be also a higher chance to identify so called SUPs (suspected unapproved parts, also „bogus parts“, chapter 20.1.2). An experienced technician who unpacks and evaluates a part/component before the assembly can recognise deviations which normally will not strike him.
Against expectation also the disassembly can add an important contribution to the safety of an aeroengine. This begins with the disassembly process itself at which a component which will be reused may not be demaged. A typical example are bolts which stuck and could be damaged during loosening.
If components of an aeroengine with alarming features are found while disassembling during overhaul or repair this can be of importance for aeroengines of the same type which are operating. Possibly a dangerous weak spot was so identified and the chance for in time remedies, inspections or monitoring exists (e.g., borescope).
The overall impression (deposits,/contamination, corrosion, soot tracks, leakages) of an aeroengine can tell the experienced technician something about the operation conditions and the maintenance. Attention and experience can avoid failures if for example during a maintenance process a dangerous scratch at a pipe is identified and this pipe will be exchanged.
What frequently is overlooked is the valuable experience which we can find in an aeroengine with a long operation time. This does not only concern valuable insights for the operator about the condition of the components/parts, but also lifetime and cost wich can be expected. Also for the OEM such findings can be very valuable. If necessary a following investigation of typical parts can pay off, especially if those don't show a visible and/or forbidden failure. From this the logistics can draw valuable conclusions.