4 Disc, spacer, or seal growth/rub 5 Creep 6 Incipient melting 7 Rub induced HCF; and 8 Blade release.
(d) The applicant should provide mandatory inspection procedures that can reliably ascertain component distress and continued airworthiness; define life reduction;
or require certain component replacement, repair, or overhaul. An applicant that has an extensive service history with derivative engines can combine that experience with OEI test results and failure mode/margin knowledge to establish the maintenance requirements with a high degree of confidence. A new type design may have to rely on design/FMEA predictions, development/certification/flight tests, and dedicated failure mode test experience to form the basis for establishing OEI usage maintenance requirements. These initial requirements could be altered later based on documented service experience and or additional development tests.
(3) Program to Validate Continued Airworthiness Instructions and Power Availability.
(a) The in-service engine evaluation program required under A33.4(b)(3) ensures the continued adequacy of the airworthiness instructions and power availability.
To achieve this goal, the applicant should collect data related to the condition of engine hardware and power availability at various stages in the life of the engine. The applicant should verify that the data satisfactorily compares with that used to define the mandatory post-flight inspection and maintenance actions at the time of engine certification. When comparing data from the in-service engines that experienced the use of 30-second and 2 minute OEI ratings with data from the certification engine following the 2-hour endurance test required under section 33.87(f), the applicant may find differences in hardware condition and power assurance characteristics. The applicant must ensure that any of these differences are properly addressed and accounted for by the mandatory inspection and maintenance actions required under this section. Otherwise, these differences, the in-service engine data, or any other supplementary data obtained by additional engine test, should be used to modify the mandatory instructions.
(b) The applicant should identify in the ALS the type of data and the procedures to collect and return the information necessary for the in-service evaluation program. To decide what data should be collected, the applicant should consider the following:
1 Whether the engine is a new type design, a derivative, or a derivative of a previously certified engine with 30-second and 2-minute OEI ratings.
2 The applicable service experience with identical or similar engine designs.
3 The certification and development test results indicating whether the OEI ratings are aggressive or conservative, or whether the use of the ratings causes 13
additional distress or no distress to the engine hardware.
4 Knowledge of failure modes and margins to failure.
(c) The in-service engine evaluation program must include some type of service engine testing and/or evaluations of service usage of the 30-second and 2-minute ratings, although equivalent service engine test experience on engines of similar design is acceptable as an alternative. This part of the program would consist of, but not be limited to, one or more of the following elements:
1 Scheduled tests of in-service engines consisting of three applications of the 30-second OEI rated power, while either installed in the rotorcraft or in an engine test cell. The engines should be selected to have sufficient service time to meet the goal described in paragraph 5.l.(3)(a) above. The program should specify the test frequency and the number of engines to be tested, as well as test parameters, necessary inspections, and data to be recorded. At a minimum, the recorded data should relate to the available power, power assurance validation, and hardware condition before and after the 30 second and 2-minute OEI rating usage.
2 Unscheduled opportunity tests of engines consisting of three applications of the 30-second OEI rated power. The program 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 program. Inspection/test requirements on such engines should include the recording of data related to available power and the identification of the hardware condition before and after the 30-second and 2-minute OEI rating usage.
3 Service usage of 30-second and 2-minute OEI rated power. This may include recorded (in service) power available data, power available data determined after the use of 30-second and 2-minute OEI ratings, and results of the mandatory inspection and maintenance actions.
4 Tests of in-service engines of similar design are also acceptable, providing they are shown to be equivalent or representative.
(d) The number of the in-service engines tested may be reduced if justified by the data obtained during the engine development or certification tests. Engine data obtained during the rotorcraft certification testing of the 30-second and 2-minute OEI ratings may be also used when it applies to engine available power and the hardware condition. Although the number of engines tested may be reduced based on certification data, the in-service engine tests under this program cannot be eliminated.
(e) During the execution of the in-service engine evaluation program, the applicant should modify the continuing airworthiness instructions as needed based on the results obtained. Similarly, if circumstances warrant, the program may need to be modified as additional in-service data becomes available.
//signed by Peter A. White// Peter A. White Acting Manager, Engine and Propeller Directorate 15
Appendix 1 APPENDIX 1. RULEMAKING BACKGROUND ON 30-SECOND OEI AND 2
MINUTE OEI RATINGS
1. The Aerospace Industries Association of America, Inc., (AIA) submitted a petition for rulemaking to the FAA on September 20, 1984, requesting an amendment to part 33 to permit type certification of engines and rotorcraft with new 30-second OEI and 2-minute OEI ratings.
2. As a result of the AIA petition, the FAA issued Notice of Proposed Rulemaking (NPRM) No. 89-27 and Supplemental Notice of Proposed Rulemaking (SNPRM) No. 89 27A, published in the Federal Register on September 22, 1989 (54 FR 39080) and February 7, 1995 (60 FR 7380), respectively. The NPRM proposed definitions and type certification standards for 30-second OEI and 2-minute OEI ratings at higher power levels than those currently available. In response to several comments, the FAA issued the SNPRM, which proposed modified definitions to 30-second OEI and 2-minute OEI ratings and minor wording changes to §§ 33.29, 33.67, and 33.85. The SNPRM also proposed a second overspeed test requirement in § 33.27 for 30-second OEI and 2-minute OEI ratings.
3. The final rule (Amendment 33-18) was published in the Federal Register on June 19, 1996 (61 FR 31324). In the final rule, the FAA adopted the proposed new definitions of 30-second OEI and 2-minute OEI power ratings. The FAA also revised requirements related to OEI ratings in §§ 33.7, 33.29, 33.67, 33.85, 33.87, 33.88, and 33.93. The proposed change to § 33.27 was not adopted because the FAA determined that certain technical aspects had not been resolved and were still under discussion with the Aviation Rulemaking Advisory Committee harmonization working group. The FAA indicated in the final rule that the overspeed test requirements for the ratings would be addressed on a case-by-case basis for each application for type certification that requests 30-second and 2-minute OEI ratings. Four special conditions that addressed overspeed test requirements for 30-second OEI and 2-minute OEI ratings for certain specific engine models were issued between 1993 and 2006.
4. A working group composed of representatives of the FAA, the Joint Aviation Authorities (JAA), Transport Canada, and industry recommended a set of harmonized certification requirements for parts 1 and 33 applicable to the 30-second and 2-minute OEI ratings. The European Aviation Safety Agency (EASA) subsequently adopted these new requirements as part of its Certification Specifications for Engines. The proposed revisions to the certification standards for § 1.1 and §§ 33.5, 33.29, 33.67, 33.87, 33.88,
33.93, and Appendix A33.4 were published on May 4, 2007 in the Federal Register (72 FR 25207). The final rule was subsequently published as Amendment No. 33-25 on August 18, 2008 in the Federal Register (73 FR 48119), effective October 17, 2008. This rule harmonizes FAA type certification standards for these ratings with the requirements of EASA in the Certification Specifications for Engines and with proposed requirements for Transport Canada Civil Aviation, thus simplifying airworthiness approvals for import and export. Subsequently, Amendment No. 33-26, which was published on August 19, 16
Appendix 1 2008, updated the requirements in § 33.28 for engine control systems and moved the requirements of 33.67(d) to 33.28(k).
Appendix 2 APPENDIX 2. EXAMPLE OF SPECIAL CONDITIONS FOR OVERSPEED TEST REQUIREMENTS OF § 33.27
1. The following is an example of the technical content of special conditions to § 33.27(b) for the 30-second OEI and 2-minute OEI ratings. For engines with 30-second and 2-minute OEI ratings, in addition to the requirements of § 33.27(b), turbine and compressor rotors should have sufficient strength to withstand the conditions specified in one of the following tests for the most critically stressed rotor component of each turbine and compressor, including integral drum rotors and centrifugal compressor, as determined by analysis or other acceptable means. We recommend selecting the test from the following paragraphs (a or b), as determined by the speed defined in paragraph a(2) or b(2), whichever is higher.
a. Test for a period of two and one-half minutes—
(1) At its maximum operating temperature except as provided in § 33.27(c)(2)(iv);
and
(2) At the highest speed determined, in accordance with § 33.27(c)(2)(i) through
(iv).
(3) This test may be performed using a separate test vehicle as desired.
b. Test for a period of 5 minutes—
(1) At its maximum operating temperature except as provided in § 33.27(c)(2)(iv);
and
(2) At 100 percent of the highest speed that would result from failure of the most critical component of each turbine and compressor or system in a representative installation of the engine when operating at 30-second and 2-minute OEI rating conditions; and
(3) The test speed must take into account minimum material properties, maximum operating temperature, and the most adverse dimensional tolerances.
(4) This test may be performed using a separate test vehicle as desired.
Following the test, rotor growth and distress beyond dimensional limits for an overspeed condition is permitted for 30-second and 2-minute OEI ratings only, provided the structural integrity of the rotor is maintained, as shown by a procedure acceptable to the FAA.