Appendix 1
6/11/09 AC 33-7A 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,
Appendix 1
6/11/09 AC 33-7A 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
6/11/09 AC 33-7A 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.