Overhauling aircraft gas turbine engines by module replacement
Overview
This standard identifies the competences you need to carry out a complete overhaul of aircraft gas turbine engines by module replacement, in accordance with approved procedures. It covers both fixed wing and rotary winged aircraft engines. The engine to be overhauled will have been removed from the aircraft and the overhauling activities may take place in a workshop or hangar.
In carrying out the overhauling operations, you will be required to follow laid-down procedures and use specific dismantling and rebuilding techniques. The overhauling activities will involve removing the engine nacelles/outer casing, removing all ancillary equipment and components and dismantling the engine down to the various sub- assembly units, such as fan case, front fan, compressor module, combustor module, turbine module and gearbox.
You will then be expected to rebuild the engine, which will involve fitting replacement or overhauled sub-assembly units (such as compressor, combustor, turbine, and gearbox) and the replacement of all damaged, worn and `lifed' components. The overhauling activities will include making all necessary checks and adjustments to ensure that components are correctly replaced, positioned, aligned, adjusted, torque loaded, locked and fastened, and that the correct sealants are used.
Your responsibilities will require you to comply with organisational policy and procedures for the overhaul of the aircraft gas turbine engine, and to report any problems with the overhauling activities or with the tools and equipment used that you cannot personally resolve, or that are outside your permitted authority, to the relevant people. You must ensure that all tools, equipment and materials used in the overhauling activities are removed from the work area on completion of the activities, and that all necessary job/task documentation is completed accurately and legibly. You will be expected to work with a minimum of supervision, taking personal responsibility for your actions and for the quality and accuracy of the work that you carry out.
Your underpinning knowledge will provide a good understanding of your work and will provide an informed approach to applying appropriate overhauling techniques and procedures to aircraft gas turbine engines. You will understand the dismantling and reassembly methods and procedures used and their application. You will know how the engine functions, the purpose of the individual components and associated defects, in adequate depth to provide a sound basis for carrying out the overhauling activities to the required specification. In addition, you will have sufficient knowledge of these components to ensure that they are fit for purpose and meet the specifications, thus providing a sound basis for carrying out the reassembly.
You will understand the safety precautions required when carrying out the overhauling activities associated with aircraft gas turbine engines, especially those for lifting, handling and supporting the equipment being removed and replaced. You will be required to demonstrate safe working practices throughout, and will understand your responsibility for taking the necessary safeguards to protect yourself and others in the workplace.
Performance criteria
You must be able to:
- work safely at all times, complying with health and safety and other relevant regulations, directives and guidelines
- follow the relevant overhauling schedules to carry out the required work
- establish the components to be removed and where appropriate, mark components to aid re-assembly
- ensure that any stored energy or substances are released, safely and correctly
- carry out the overhaul to the agreed level, using the correct tools and techniques
- ensure that all removed components are correctly identified and stored in the correct location
- replace/refit components using appropriate methods and techniques
- carry out checks on the overhauled engine using correct procedures
report any instances where the overhauling activities cannot be fully met, or where there are identified defects outside the planned overhauling schedule
complete the relevant documentation, in accordance with organisational requirements
- dispose of unwanted components, waste materials and substances, in accordance with safe working practices and approved procedures
- deal promptly and effectively with problems within your control and report those that cannot be solved
- leave the engine in a safe and appropriate condition, free from foreign object debris and in a condition ready for ground running
Knowledge and Understanding
You need to know and understand:
- the specific safety practices and procedures that you need to observe when dismantling and replacing aircraft gas turbine engine modules (including any specific legislation, regulations/codes of practice for the activities, equipment or materials)
- the importance of maintenance on and impact upon (extended twin operations procedures) ETOpS systems, legislation and local procedures
- the health and safety requirements of the area in which the dismantling and module replacement activity is to take place, and the responsibility these requirements place on you
- the requirements and importance of understanding and applying human factors as defined by the regulatory requirements and the potential impact if these are not adhered to
- the hazards associated with dismantling and replacing aircraft gas turbine engine modules (such as handling oils, greases, aviation fuel, stored pressure/force, use of power tools, misuse of tools, using damaged or badly maintained tools and equipment, not following laid-down overhauling procedures, lifting and moving large and heavy components) and how to minimise them and reduce any risks
- the importance of wearing protective clothing (PPE) and other appropriate safety equipment during the dismantling and module replacement activities
- how to obtain and interpret drawings, specifications, manufacturers' manuals, history/maintenance reports, and other documents needed in the overhauling process
- how to carry out currency/issue checks on the specifications you are working with
- the quality control procedures to be followed during the overhauling operations
- the procedure for obtaining replacement parts, materials and other consumables necessary for the overhaul
- company policy on the repair/replacement of components during the overhauling process
- terminology used in aircraft gas turbine engines and engine modules
- the principles of how the engine functions and the working purpose of individual modules/units
- the extent to which the equipment is to be dismantled for the overhaul
- the sequence to be adopted for the dismantling/reassembling of various types of engine assemblies
- the techniques used to dismantle the aircraft gas turbine engines without damage to the components or surrounding structure (such as release of pressures/force, draining of fluids, making electrical disconnections, proof marking components to aid reassembly, removing assemblies requiring pressure/force, removing mechanical locking and securing mechanisms/devices)
- the need to protect the system integrity by ensuring that exposed components are correctly covered/protected
- how to lift and move large components and assemblies; the methods and equipment used to transport, handle and lift the components during the overhauling activities
- the need to ensure that lifting and handling equipment is within its current certification dates
- methods of checking that components are fit for purpose, how to identify defects and wear characteristics, and the need to replace `lifed' items (such as seals and gaskets)
- the uses of measuring equipment (such as micrometers, Verniers, expansion indicators and other measuring devices)
- methods of reassembling the aircraft gas turbine engine, using new or previously overhauled modules (such as replacing assemblies requiring pressure/force, ensuring correct orientation and alignment of modules, replacing mechanical locking and securing mechanisms/devices, reconnecting pipes and electrical connectors)
- how to make adjustments to replaced components/assemblies to ensure that they function correctly (such as checking alignment, balancing of rotating components such as turbines, setting working clearance, setting travel, and pre-loading bearings)
- the various mechanical fasteners that are used and their method of removal and replacement (including rivets, threaded fasteners, special securing devices)
- the various types of electrical connector that are used, methods of unlocking, orientation indicators and locating and locking in of the connections
- why electrical bonding is critical and why it must be both mechanically and electrically secure
- the tools and equipment used in the overhauling activities and how to check that they are in a safe, tested and usable condition
- the importance of ensuring that all tools are used correctly and within their permitted operating range
- the importance of ensuring that all tools, equipment and components are accounted for and returned to their correct location on completion of the overhauling activities
- the procedure for the safe disposal of waste materials
- the generation of maintenance documentation and/or reports following the overhauling activity
- the problems that can occur during the overhauling activity and how they can be overcome
- the extent of your own authority and to whom you should report if you have a problem that you cannot resolve
Scope/range
Scope Performance
Carry out all of the following during the overhaul of the aircraft gas turbine engine:
- obtain and use the appropriate documentation (such as job instructions, engine overhaul manuals, engineering drawings, technical instructions and other relevant maintenance documentation)
- adhere to procedures or systems in place for risk assessment, COSHH, personal protective equipment and other relevant safety regulations and procedures to realise a safe system of work
- provide and maintain safe access and working arrangements for the overhauling area
- obtain the correct tools and equipment for the activity and check that they are in a safe, tested and usable condition and within current certification/calibration date
- ensure that all oils, fluids and fuel have been drained/removed before breaking into the system
- ensure that the engine is suitably supported and that appropriate lifting and handling equipment is available
- carry out the overhauling activities, using approved techniques and procedures at all times
- ensure that components and surrounding structures are maintained free from damage and foreign objects
- return all tools and equipment to the correct location on completion of the activities
Carry out a major overhaul of one of the following types of aircraft gas turbine engine:
- turbo prop
- turbo jet
- turbo-fan
- ducted fan
- turbo-shaft
- ground turbine start (GTS)
Dismantle aircraft gas turbine engines, to include removing four of the following sub-assemblies:
- fan case
- exhaust/reheat assembly
- combustor module
- turbine
- front fan
- compressor module
- by-pass duct
- gear box
Carry out all of the following activities on the equipment being overhauled:
- pre-disassembly checks
- replacing all 'lifed' items (such as seals, bearings, gaskets)
- removing engine nacelles/outer casing
- disconnecting and removing wires/cables, and attaching suitable cable identification markers
- applying gaskets and sealant/adhesives
- replacing all damaged or defective sub-assemblies and components
- disconnecting and removing pipework
- removing all ancillary components
- re-assembling components to sub-assembly level
- dismantling equipment to unit/sub-assembly level
- re-assembling sub-assemblies to unit level
- dismantling units to component level
- setting and adjusting replaced components
- removing and replacing components having interference fits (such as by expansion, contraction, pressure)
- refitting all ancillary components
- reconnecting all pipework
- refitting cable harnesses
- proof-marking/labelling of components to aid reassembly
- refitting electrical units and connecting to cables
- electrical bonding of components
- checking components for wear and serviceability
- tightening fastenings to the required torque
- securing components using mechanical fasteners and threaded devices
- applying bolt locking methods (such as split pins, wire locking, lock nuts, stiff nuts, swage nuts)
Replace/refit a range of engine components and sub-assemblies, to include: four of the following engine modules:
- fan case
- combustor module
- front fan
- turbine
- compressor module
- gear box
- exhaust/reheat assembly
- by-pass duct
plus eight of the following types of component:
9. curvic couplings
10. wire thread inserts
11. bearings
12. pipes and unions
13. static seals/gaskets
14. mechanical controls (such as plungers, springs, rollers)
15. dynamic seals
16. shims and packing
17. electrical units and controls (such as solenoids, motors, switches)
18. mechanical securing devices
19. locking devices
20. other specific components
Carry out checks and tests on the overhauled engine, to include six of the following:
- positional accuracy
- operating/working clearance
- orientation
- electrical checks (such as continuity and earth bonding)
- alignment
- visual inspection for completeness and freedom from damage or foreign objects
- freedom of movement
- bearing end float
- 'special-to-type' test rig checks
Complete the relevant paperwork, to include one of the following and pass it to the appropriate people:
- job cards
- computer records
- aircraft log books
- engine overhaul logs or reports
- work authorisation documents
- permit to work/formal risk assessment and/or sign-on/off procedures
- shift handover documentation
Overhaul aircraft gas turbine engines in compliance with one of the following:
- Civil Aviation Authority (CAA)/European Aviation Safety Agency (EASA)
- extended twin operations procedures (ETOpS) (where appropriate)
- Ministry of Defence (MoD)
- Military Aviation Authority (MAA)
- Aerospace Quality Management Standards (AS)
- Federal Aviation Authority (FAA)
- BS, ISO or BSEN standards and procedures
- customer standards and requirements
- company standards and procedures
- engine manufacturer's requirements
Scope Knowledge
Values
Behaviours
You will be able to apply the appropriate behaviours required in the workplace to meet the job profile and overall company objectives, such as:
- strong work ethic
- positive attitude
- team player
- dependability
- responsibility
- honesty
- integrity
- motivation
- commitment