AMC E 25 Instructions for continued airworthiness

(1)The maintenance actions are determined through certification testing, including, where applicable, endurance tests, initial maintenance programme test, over-speed tests, over-temperature tests, and supplemented by development testing and service experience of Engines of the same type or of similar design. Servicing information should cover maintenance details regarding servicing points, inspections, adjustments, tests and replacement of components if required.

The mandatory inspection and maintenance actions considered under CS-E 25(b)(1) may also evolve after entering service, based on the service experience.

(2)Where it is permitted to carry out certain tests with the engines installed in the aircraft, the relevant manual(s) should provide information on the way in which minimum installed performance levels will be verified (if necessary) and related to the static sea-level test-bed ratings approved for the Engine.

(3)The manuals required under CS-E 25 should include, where applicable, details of the division of the Engine into modules, giving the nomenclature and clearly defining the boundaries for each module.

(4)Inspection and maintenance actions for engines having 30-Second and 2-Minute OEI Power ratings. (See CS-E 25(b)(2))

(a)For Engines with 30-Second and 2-Minute OEI Power ratings, the airworthiness limitations section of the instructions for continued airworthiness are required to prescribe the mandatory post-flight inspections and maintenance actions which are applicable following the use of either of these two ratings, or both, prior to next flight.

If the 2-Minute OEI Power rating time period is extended to 2 1/2 minutes, as described in paragraph (5) of AMC E 40(b), the additional 30- second period is considered as a de-rated 30-Second OEI Power rating and the maintenance actions prescribed for the 30-Second OEI rating should be used. Alternatively, the applicant may seek approval for prescribing a different set of inspections and maintenance actions for time exceedence of Engine operation at the 2-Minute OEI Power rating if this is appropriately justified and validated. For instance, if the Engine is essentially the same as one which has a 2 1/2-Minute OEI rating equivalent to the new 2-Minute OEI rating, then the maintenance considerations of the 2 1/2-Minute OEI rating might also be applicable after use of the 2-Minute OEI rating for up to 2.5 minutes.

If only the accumulated usage time is recorded under CS-E 60(d)(2), the inspection and maintenance action prescribed as required by CS-E 25(b)(2) should be based on the total recorded time duration regardless of the number of applications at the ratings used in one flight.

(b)The 30-Second and 2-Minute OEI ratings were originally intended to allow brief periods of operation close to the limits of the Engine design. This may result in component deterioration beyond serviceable limits so that they would not be suitable for further use.

The extent to which use of the ratings cause component damage or life reduction, in particular the life of Engine Critical Parts, is primarily a function of Engine design margins, application exposure level and duration, hardware condition prior to use and operating environment. Because Engine operating conditions and time recording are specifications for this rating, the maintenance actions can be related directly to an actual documented usage level, time and, if applicable, known condition prior to rating application (hours / cycles / prior rating exposure, etc.).

Depending on the actual operating parameters such as temperature and time exposure which are recorded during usage of these ratings in accordance with CS-E 60(d), it is possible to pre-define a maintenance action and decrement of the remaining time before overhaul or component replacement, based on the type, level and duration of exposure. If the mandatory maintenance instructions result in no maintenance action, then the minimum specification would be the interpretation of recorded event data and documentation of the data in the maintenance log(s). The instructions for continued airworthiness should also include the definition of data to be provided by the operator on the Engine during service to support the applicant in completing the Engine in service evaluation programme

(c)Validation of mandatory post-flight inspection and maintenance actions.

(i)Under CS-E 40(f), at any time during its service life, the Engine should be maintained in a condition which would assure that the 30-Second and 2-Minute OEI ratings can be attained and sustained. This specification has a bearing on both power assurance procedures and instructions for continued airworthiness. The mandatory maintenance following the use of 30-Second or 2-Minute OEI rating should be capable of identifying and correcting any component distress which could significantly reduce subsequent Engine reliability or prevent the Engine from achieving or sustaining further application of the OEI ratings.

The applicant should provide evidence by endurance test results or analysis based on test data of the endurance tests, and/or with other certification tests and service experience of similar type and design of engines, to show that the power at 30-Second and 2-Minute OEI ratings is achievable and can be sustained for the respective duration at any time between overhauls or major maintenance of the Engine.

(ii)Essential to the establishment of mandatory maintenance instructions is a thorough knowledge of the potential damage incurred with use of the 30-Second and 2-Minute OEI ratings and, more importantly, the remaining margin to component Failure or reduced Engine performance due to use of these OEI ratings.

The certification procedures for the 30-Second and 2-Minute OEI ratings emphasise demonstrating design adequacy by endurance testing and by specific margin tests for turbine temperature, rotor speeds, etc. An understanding of operating margins to various Failure modes when operating at the 30-Second and 2-Minute OEI ratings is needed for establishing adequate instructions for continued airworthiness. These Failure modes should be determined and validated by appropriate methods or experience.

(iii)The applicant should undertake the necessary actions, including instructions in Engine manuals, to make sure that the operators are aware of the need and understand the procedures to properly collect and return the information necessary for the applicant to monitor the adequacy of the prescribed mandatory maintenance actions.

(d)In-service Engine evaluation programme

(i)In order to comply with CS-E 25(b)(2), an in-service Engine evaluation programme to assure the continued adequacy of the instructions for continued airworthiness and of power availability data should be provided and be approved by the Agency prior to certification.

The intent of this programme is to obtain relevant data concerning Engine hardware condition and power availability at various stages in the life of the Engine hardware critical to the achievement of the ratings and to compare that data to corresponding data observed during the certification process that defined the instructions for continued airworthiness.

Differences may exist in hardware condition and power availability characteristics from in-service engines that have not experienced any usage of the 30-Second or 2-Minute OEI ratings versus similar parameters that existed prior to the two-hour additional endurance test of CS-E 740(c)(3)(iii).

Similarly, differences may exist in hardware condition and power assurance characteristics from in-service engines after usage of the 30-Second or 2-Minute OEI ratings versus similar parameters observed following the two-hour additional endurance test of CS-E 740(c)(3)(iii).

Proper definition of the instructions for continued airworthiness is expected to have anticipated and accounted for such in-service conditions; this programme should however be structured to validate that such in-service differences are properly accounted for. If the data obtained during the execution of the programme indicates that the in-service differences are not properly accounted for, then the data from the programme or from additional Engine testing should be used to modify the instructions as appropriate.

(ii)The in-service Engine evaluation programme should include some type of service Engine testing and / or evaluations of service usage of the 30-Second / 2-Minute OEI ratings, although equivalent service Engine test experience on engines of similar design is acceptable as an alternative. This part of the programme would consist of, but not be limited to, one or more of the following elements:

Scheduled tests of in-service Engines imposing three applications of 30 seconds OEI rated power, while either installed in the rotorcraft or in an Engine test cell. For selected representative aged engines, the programme would include number and frequency of samples, as well as inspection and test specifications. Such specifications should include the recording of data on the available power and the identification of the hardware condition before and after 30-Second and 2-Minute OEI rating usage.

Unscheduled tests of engines of opportunity imposing three applications of 30 seconds OEI rated power. The programme may include actions to be taken when Engines become available that meet certain predetermined criteria. Definition of selection criteria for representative aged engines should be included in the programme. Inspection / test specifications on such engines should include the recording of data on the available power and the identification of the hardware condition before and after 30-Second and 2-Minute OEI rating usage.

Service usage of 30-second/2 minute OEI rated power. This may include recorded power available data, post usage power available data and / or results of the mandatory maintenance and inspection actions.

The equivalent service test on engines of similar design is acceptable although it should be demonstrated as being representative.

The aircraft certification testing of the 30-Second and/or 2-Minute OEI ratings could also provide additional recorded data with respect to available power, post-usage power data and results of hardware maintenance and inspection of the Engine, to support the programme.

In addition to the tests on engines from service, the in-service evaluation programme may also include test evidence from development or certification tests to reduce, but not eliminate, the required number of engines from service.

During the execution of the in-service evaluation programme, the instructions for continued airworthiness should be modified as necessary, based on the results. Similarly, if circumstances warrant, the programme itself may be modified, as additional in-service data become available.

(iii)The information or actions needed from the operator to support the in-service evaluation programme may be prescribed in the airworthiness limitation section of the instructions for continued airworthiness.

(5)For an Engine with a 30-Minute Power rating, the usage of this rating should be considered in the establishment of instructions for continued airworthiness. Usage limitations, such as the cumulated time limit for the 30-Minute Power rating, should be specified in the appropriate section of the ICA. Instructions should also be included for when these limits are reached.

(6)The applicant for the certification of a piston Engine may substantiate a time between overhauls (TBO) or a time between replacements (TBR). TBO is a recommended number of running hours or calendar time before the Engine requires overhaul. TBR is a recommended number of running hours or calendar time before the Engine requires replacement (instead of overhaul). The substantiation of the recommended TBO/TBR running hours should be performed as follows.

(a)The applicant may use the 150-hour endurance test required by CS-E 440 for the substantiation of the TBO/TBR. The applicant may then propose a TBO/TBR ranging between 600 flight hours (e.g. for fully new designs) and 1 000 flight hours (e.g. for derivative designs). The TBO/TBR value should be agreed by EASA.

(b)If the applicant wishes to propose a TBO/TBR higher than what the CS-E 440 test allows it to substantiate (see paragraph (6)(a) above), then the following method may be used.

(i)An additional Engine cyclic durability test should be run on an Engine representative of the type design.

(ii)The cycle profile should be based on estimated aircraft flight profiles.

(iii)The number of cycles should be representative of the TBO/TBR intended to be declared and should represent a level of Engine deterioration at least equivalent to that of an Engine at the end of the intended TBO/TBR.

(iv)The instructions for continued airworthiness associated with the intended TBO/TBR should be performed and validated during the Engine cyclic test.

(v)Complementary analysis and/or testing should be provided to support any aspects not adequately demonstrated throughout the Engine cyclic durability test.

(vi)If it is proposed to subject the tested Engine to any kind of strip examination during the test in order to validate an interim TBO/TBR, it should then be shown that cleaning or replacement of any seal or component (e.g. bolts) during reassembly of the Engine will not favourably influence the outcome of the test.

(vii)Past experience with Engines of similar design and/or in-service operation, where applicable, may also be used as alternative evidence to support or complement the proposed TBO/TBR. The credit taken for the duration of such cyclic durability test should use a factor of 1, unless the applicant can justify, and EASA accepts, a higher value.

(c)The applicant may also include a calendar time in the recommended TBO/TBR that takes into account Engine components degradation that are time dependent, such as ageing of some material, corrosion, etc.

(d)The TBO/TBR should be declared, and the necessary corresponding instructions (e.g. an Engine overhaul manual when using a TBO) should be provided, as required by CS-E 25(a).

[Amdt No: E/1]

[Amdt No: E/5]