Leaflet 70-80 Guidance Material for Ageing EngineContinuing Airworthiness1 Introduction1.1 This guidance material has been produced following a number of accidents over a period, involving the serious failure of high calendar time engines or their accessories. Over a prolonged calendar time engine parts risk deterioration due to corrosion and the hardening of materials such as seals, gaskets, diaphragms and flexible pipes. This leaflet has been compiled to accommodate historic engine types and their ancillary equipment which are typically without manufacturer-recommended calendar time backstops available.1.2 The intention of this guidance is to provide continuing airworthiness recommendations for the management of engines against potential calendar time related deterioration. This is particularly relevant to certain categories of non-EASA aircraft types where the product is no longer actively supported by the engine manufacturer. If the Original Equipment Manufacturer (OEM), does not provide any recommended calendar time between overhauls, under a low utilisation operation regime, this can result in an engine remaining on wing for a protracted period before removal for workshop strip/overhaul under the TBO limit (in hours or cycles run). This guidance provides a framework of generic best practices as examples of how to allow ageing engines to continue to operate with acceptable standards of continuing airworthiness.2 Applicability2.1 This guidance is intended specifically for the following categories of fixed and rotary wing aircraft and engines:a) Non-EASA aircraft types with National Certificates of Airworthiness powered by gas turbine engine(s) or by radial piston engine(s) of > 400 hp;b) Ex-military aircraft with National Permits to Fly powered by gas turbine engine(s) or radial piston engine(s) of > 400hp.Complex aircraft types and their engines, however, are not covered by this guidancematerial.2.2 While aimed at a specific group of high calendar time engines, owners and operators of other high time engines can consider the practices and the need for additional maintenance actions to ensure appropriate standards of continuing airworthiness are upheld. The principles laid out in this document may be useful for this purpose.3 Engine Manufacturer’s Recommendations3.1 Typically ageing and ex-military engines do not have calendar time recommendations between overhaul quoted in the manufacturer’s instructions for continuing airworthiness. Any limitations that have been imposed by the OEM, however, must be respected, such as whole engine and critical part hard lives, and cycle/hour times between overhaul, whichever come first. Furthermore, ancillaries must be controlled within their OEM recommended lives. Other instructions such as maintenance tasks, frequencies and inspections, as well as those for ancillary equipment should be respected.4 The Maintenance Organisation (MO) Environment4.1 In the context of ex-military Permit to Fly aircraft and National Certificate of Airworthiness aircraft with large radial piston or gas turbine engines (as defined in paragraph 2, titled Applicability, above) it is expected that the aircraft will be maintained by a suitably approved organisation (such as a BCAR A8-20/A8-23 approved maintenance organisation, or appropriate equivalent). This organisation will accordingly have responsibility for the control of engine records (including storage), hazard analysis and management of scheduled tasks within the Maintenance Schedule including a regular review of the effectiveness of the programme.5 Hazard Risk Assessment5.1 BCAR A8-20/A8-23 appropriately approved maintenance organisations can where applicable conduct a hazard risk assessment on the continuing airworthiness aspects of the operation of engines with prolonged calendar lives since new or last overhaul to establish the levels of maintenance required. Potential areas of consideration can include but not be limited to:a) Multiple engine and system applications with adequate redundancy and safety margin;b) The safety record of the specific type, taking into account UK and worldwide events, the specific failure modes and their consequences;c) The likelihood of any safety critical failure modes such as in-flight fire, uncontained failure or propeller release;d) The consequences of the loss of thrust of a single engine;e) Any systems or measures which can realistically be used to mitigate against the consequences of a significant failure event.If a Hazard Risk Assessment (HRA) is carried out as a means of compliance against this guidance material a formal review process should be carried and a documented report compiled.6 Alternative Means of Compliance6.1 In the absence of OEM calendar time limitations on engine overhaul periods, CAP562 Chapter 70 Leaflet 70-80 at Page3, Table 1 illustrates the option either to remove from service engines which have reached or exceeded 20 years of service since last recondition, overhaul or termination of last accepted storage period, or through an appropriately approved organisation (e.g. BCAR A8-20 Maintenance Organisation), construct a customised Alternative Means Of Compliance (AMOC) programme.6.2 It is possible that AMOCs could include a broad spectrum of in-service monitoring, inspection and partial disassembly actions (which may vary across different engine types) to verify that acceptable standards are being maintained, and to ensure that age-related deterioration is addressed. The basic elements and considerations of an AMOC are covered in the sections below.7 Maintenance Programmes/Schedules7.1 It is considered important that the MO compiles a customised Maintenance Programme (MP) that reflects all engine on-wing and off-wing scheduled AMOC maintenance such as inspections, trend monitoring, workshop visits, and partial disassemblies where necessary. An MP should include references to the OEM’s data such as manuals, instructions, bulletins and service letters where applicable. Similarly any modification or de-modification status should be reflected.7.2 The scheduled engine maintenance and inspection tasks that constitute the AMOC (including those required to be carried out off-wing, in a workshop) should be integrated with the higher level aircraft MP.7.3 The elements needed for a particular programme aimed at developing an AMOC will depend upon the outcomes of the hazard assessments, data collection, analysis and review functions as outlined in Table 1 of paragraph 6.1 above. Paragraphs 8 and 9 below detail some generic items which might be considered for inclusion in any possible programme, but it is accepted that the details of each individual programme will vary depending on the results of the preparatory work and the specific issues pertinent to the type being reviewed.8 Gas Turbine Engines – Generic or Possible AMOC Elements8.1 Particularly relevant for gas turbine engines, where possible the following data could be considered for collection at each engine run, as permitted by the type:a) Pilot reports;b) Oil consumption rates/trend monitoring;c) Gas path performance trend monitoringd) (e.g. TGT, spool speed, etc.);e) Engine run down times;f) Vibration monitoring (if system equipment is fitted);g) Engine running times (including ground runs).8.2 The above information should be formally recorded as relevant for each flight, and issues such as gas path parameters, vibration, and oil consumption trending plotted for evidence of datum shifts. It is quite likely that the optimum health monitoring could be carried out by flight crew at a steady state phase of engine operation.8.3 Further maintenance tasks relevant to the AMOC may not be limited to those listedbelow as follows:a) Borescope inspections of gas path components;b) Hot section inspections (with or without combustor removal);c) Compressor inspections with compressor half case removal;d) Oil filter element sectioning and analysis;e) Oil analysis (i.e. SOAP);f) Fuel contamination checks;g) Magnetic Chip Detector (where fitted) findings and recorded history;h) Jet pipe inspections for corrosion, cracking (particularly of circumferential welds) and evidence of damage;i) Bleed valve check/inspection;ii) j) Module changes;iii) k) Compressor water washes under OEM’s instructions.8.4 Inspections should clarify which areas and how the inspection is to be carried out. For example compressor inspections should clarify whether rotating blades, static vanes and rotor path linings are inspected, and at which stages. If engine design and the manufacturer’s instructions permit, then periodic compressor inspections, with the top casing removed, allow for a more thorough inspection to be carried out. Similarly, combustor-can removal could provide a useful insight into the status of combustor and initial turbine stage conditions. Inevitably, some inspections may require the removal of the engine from the airframe.An example of possible generic AMOC inspections for consideration on gas turbine engines is provided in CAP562 Chapter 70 Leaflet 70-80 Page 5.9 Large Radial Piston Engine – Generic or Possible AMOC Elements9.1 Along similar lines to the operation of gas turbine engines, the following data should be collected following the operation of large radial engines, such as:a) Pilot reports;b) Oil consumption rates/trend monitoring;c) Engine running times (including ground runs);9.2 Additional piston engine checks and inspections could include but not be limited to the following:a) External engine inspection including crankcase and cylinder inspections;b) Cylinder compression including differential pressure checks;c) Borescope Inspection;d) Oil and fuel analysis;e) Engine power checks;f) Checks for evidence of hydraulic locking.9.3 Tasks involving partial engine disassembly to ensure against the onset of the effects of age deterioration could include the following:a) Removal and inspection of cylinder heads;b) Removal and inspection of cylinders;c) Disassembly of pistons, gudgeon pins and connecting rods for conditioninspection;d) Crankshaft inspection in-situ;e) Crankcase inspection in-situ.An example of additional generic AMOC inspections for consideration on large radial piston engines is shown on Pages 6 and 7 of CAP562 Chapter 70 Leaflet 70-80.10 Utilisation of Approved Maintenance Organisations10.1 Appropriately approved maintenance organisations (e.g. BCAR A8-20/A8-23) are required to carry out all maintenance tasks (whether in the AMOC or otherwise) in accordance with the OEM’s maintenance manual instructions.10.2 It is acknowledged that some of the tasks involved in engine continuing airworthiness may have transitioned in the AMOC package from the dedicated workshop (where these tasks were originally carried out) into the aircraft base maintenance environment. The maintenance organisation has responsibility to ensure that all staff involved in the engine maintenance activity (including the AMOC) are assessed and controlled for appropriate experience, competence and training to carry out the tasks prescribed. Whatever the task, the maintenance organisation should ensure that it has available the appropriate tooling and equipment, approved data and contamination free environment to carry out any engine maintenance operations (including those requiring partial disassembly and complex activities).Cylinder Borescope – Carry out internal borescope inspection of each cylinder via spark plug hole, recording and assessing the condition of valves, piston crown, cylinder head and cylinder walls.12 monthly Engine Oil Condition – Send sample of engine oil for SOAP oil analysis. Remove, inspect and clean oil sump plugs and oil screens as applicable.12 monthly Engine Filters/ Screens – Replace, section and examine fuel and oil filter elements where applicable for evidence of debris. Collect filter debris for inspection, analysis and future reference.12 monthly Power Runs – Carry out engine ground power assurance check. 12 monthlyAncillary Equipment Remove for overhaul, disassembly and bench test ancillary components (such as magnetos, carburettors, pumps, control units etc).4-6 yearly Crankshaft/Reduction Gear Assembly – Carry out in-situ inspection of crankshaft/reduction gear assembly for signs of corrosion, cracking deterioration (e.g. along propeller attachment splines), viewing as much of the crankshaft as is accessible or possible.3-6 yearly or at propeller removal opportunity (whichever is soonest) – Flexible Hoses Inspect, replace, pressure test flexible hoses in accordance with OEM’s recommendations. CAP 562 Book 2, Leaflet 20-50 provides some generic test details.2-8 yearly intervals – Cylinder Base Nut CheckBreak torque check on cylinder bolts, to ensure bolts are not backing off.3 yearly – Zones Large Radial Piston Engine – Inspection Type Frequency 11 Safety Critical Tasks11.1 Whenever multi-system maintenance is carried out on aircraft systems including engines, fuel etc, the Maintenance Organisation shall establish procedures to minimise the risk of multiple errors by individual maintenance personnel during a single line or base activity (the principles of BCAR A8-23 paragraph 15.2 c) refer).12 Engine Records12.1 The retention of full engine records is necessary for the confidence of the continuing airworthiness programme. Therefore, the following issues should be accommodated:a) Details of last restoration or overhaul (dates etc.) activities;b) Completion of engine operation hours and cycles in log books (including for ground running);c) Strict disc, drum and shaft (i.e. critical part) life logging and controls within the framework of OEM declared lives;d) Evidence of compliance with Mandatory Permit Directives (MPDs) andAirworthiness Directives (ADs) as applicable;e) Retention of maintenance workpack details;f) Engine storage details – compliance with OEM’s instructions (refer to 13.1 below for clarification).13 Engine Storage13.1 Installed engines which are used only infrequently should be either run periodically or inhibited and stored in accordance with manufacturer’s instructions. Removed engines should be stored and sealed as detailed by the engine OEM’s recommendations. Maintenance organisations regularly involved in the storage and inhibiting of engines should consider establishing procedures and work sheets based on the manufacturer’s instructions, which include maintaining the engine storage status within the records. Engine log books and records should clarify the dates and extent of system inhibition/de-inhibition, providing details where relevant.14 Periodic Review14.1 MOs wishing to utilise the AMOC option should periodically review the effectiveness of their reliability programmes by utilising findings and feedback data as well as workshop findings/strip reports on a regular basis, as formalised under their organisation’s procedures.15 AMOC Management15.1 It is the responsibility of the appropriately approved Maintenance Organisation (e.g. BCAR A8-20/A8-23 or equivalent) to manage the AMOC package (under its privileges) as an alternative to a 20 year calendar life to recondition or overhaul the engine in a workshop environment, and to reflect all elements of the package within the aircraft level Maintenance Programme.16 Mandatory Permit Directive (MPD) and Airworthiness Directive (AD)Compliance16.1 Where the guidance information provided in this leaflet conflicts with an MPD or an AD (either already in existence or in the future) against an aircraft/engine type, the MPD/AD must still be complied with.Reference:CAP562 – Book 2 Chapter 70 Leaflet 70 -80 issued 31st October 2012 providing continuous airworthiness recommendations for the management of engines against potential calendar time related deterioration.
Pete WoollacottSenior Airworthiness Surveyor CAA Gatwick Regional OfficeAviation HouseGatwick Airport tel: +44 (0)1293 768637mob: +44 (0)771 2751055