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CFR NPRM
 Federal Register Information
[Federal Register: February 14, 1985 (Volume 50, Number 31)]
[Page 6186]
Header Information
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 33
[Docket No. 24466; Notice No. 85-6]
Airworthiness Standards; Aircraft Engines, Engine Control Systems
Preamble Information
AGENCY: Federal Aviation Administration, DOT
ACTION: Notice of Proposed Rulemaking
SUMMARY: This notice proposes to establish requirements for the certification of electronic aircraft engine control systems. Such control systems have already been developed for turbine engines and the potential exists for reciprocating engine applications. Electronic control systems, however, have unique characteristics which are not addressed in the current regulations pertaining to engine controls. Therefore, this proposal would add a new section to Federal Aviation Regulations (FAR) Part 33, to establish uniform functional standards specifically designed for electronic controls.
DATES: Comments must be received on or before May 20, 1985.
ADDRESSES: Comments on this proposal may be delivered or mailed in duplicate to: Federal Aviation Administration, Office of the General Counsel, Room 916, Attention: Rules Docket No. 24466, 800 Independence Avenue, S.W., Washington, D.C. 20591.
Comments may be examined in the Rules Docket weekdays, except Federal holidays, between 8:30 a.m. and 5:00 p.m.
FOR FURTHER INFORMATION CONTACT: H. Alden Jackson, Engine and Propeller Standards Staff, ANE-110, Federal Aviation Administration, New England Region, 12 New England Executive Park, Burlington, Massachusetts 01803; telephone (617) 273-7078.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Comments relating to the environmental, energy, or economic impact that might result from adoption of the proposals contained in this notice are invited. Comments are specifically requested concerning the implementation and effective date of the final rule. The FAA proposes to establish an effective date of 180 days after the issuance of the final rule. All initial comment received on or before May 20, 1985, and all reply comments received on or before July 20, 1985, will be considered by the Administrator before taking action on the proposed rule. The proposal contained in this notice may be changed in the light of comments received. Communications should identify the regulatory docket or notice number and be submitted in duplicate to the address specified above. All comments submitted will be available for examination in the Rules Docket both before and after the closing date for comments. Commenters wishing the FAA to acknowledge receipt of their comments on this notice must submit with those comments a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket No. 24466". The postcard will be date/time stamped and returned to the commenter. A report summarizing each substantive public contact with FAA personnel concerned with this rulemaking will be filed in the docket.
Availability of NPRM
Any person may obtain a copy of this Notice of Proposed Rulemaking (NPRM) by submitting a request to the Federal Aviation Administration, Office of Public Affairs, Attention: Public Information Center, APA-430, 800 Independence Avenue, S.W., Washington, D.C. 20591, or by calling (202) 426-8058. Communications must identify the notice number of the NPRM. Persons interested in being placed on a mailing list for future NPRM's should also request a copy of Advisory Circular No. 11-2 which describes the application procedures.
Background
State-of-the-art technology has let to the development of more complex and more nearly automated control systems for aircraft engines. This is particularly true in the cases of electrical and electronic engine control systems. Although electronic controls have, so far, only been developed for turbine engines, the potential exists that they may be developed for future use with reciprocating engines. Presently, there are no established definitive regulations that provide the certification basis for these engine control systems. The FAA has in recent years relied upon generalized interpretations of the FAR, Advisory Circular information, and certain aviation committee documentation to allow for such certification on a case-by-case basis. Therefore, the need has become evident for an addition to Part 33 of the FAR that establishes and standardizes the certification basis for electrical and electronic engine control systems for both turbine-powered and reciprocating-powered engines.
Electronic controls vary from a simple trimming device with full hydromechanical control backup to a complex, full authority, digital system with no mechanical backup. The operation of mechanical and analog electronic control systems may be verified by testing, since measured outputs are continuous functions of known inputs and dedicated hardware is used to perform each function. However, control systems based on digital computer technology are discontinuous and use shared hardware resources which cannot be completely tested. Although discontinuities can be made small, they raise the problem of finding if any are larger than expected and finding the set of circumstances which would cause them to occur. Undiscovered software errors which could cause significant discontinuities, rather than failures, are the primary concern. As all engines on an aircraft could experience such as effect simultaneously, the resulting loss of power could be greater than a single engine failure. To identify these discontinuities by testing would require tests for each and every combination of individual inputs. Since this is impractical, the method used for the design of the system software must be a part of the certification review.
It has been a consistent certification requirement that engine operational integrity must be isolated from dependence on aircraft power or data inputs. This requirement shall continue with respect to electronic controls. Therefore, if aircraft power or data is used, a loss of either must not result in a significant change in engine operation.
Continued safe operation must be provided in the event of failures of the electrical or electronic components over a required range of power or thrust. Judgment must be used in establishing the required range, which depends on the intended application of the engine. The proposal concerning component failures is intended to permit flexibility and not impede design improvements or impose economic penalties, such as excessive redundancy, in the configuration of the control systems.
Lightning is a potential hazard which, in the past, has been primarily associated with the fuel within a fuel system and not the control of the fuel system. With the advent of electronic engine controls and the increased use of aircraft composite materials, however, the possibility exists that lightning strikes may affect engine operation. Therefore, the maximum level of lightning induced transients, which the control system can tolerate, must be specified for certification.
Economic Impact
There is no known increased cost impacts over current industry practice associated with the proposed rule. This proposed rule codifies and standardizes the existing FAA practice with regard to the certification of engine control systems, particularly with those systems that are electrical or electronic in nature and more recently with the full authority digital electronic control (FADEC) system of the Pratt & Whitney 2037 turbine engine. Because these systems are state-of-the-art and there are presently no definitive regulations which provide for their certification, the FAA has relied upon generalized interpretations of the FAR, Advisory Circular information, and other aviation committee documentation to allow for certification on a case-by-case basis. The FAR rules which have been applied generally to the certification of electronic and electrical engine control system include Part 25.901, Installation; Part 33.75, Safety Analysis; and Part 33.91, Engine Components Tests. None of these rules, however, provide explicit requirements with regard to engine controls. In consonance with existing FAA practice, this proposed rule underlies the FAA's intent to promulgate a regulation which institutes functional objective requirements rather than mandate design requirements in order to accomplish the certification of engine control systems.
Proposal 1 requires that control systems which rely on electrical or electronic means for operation must have the degree of authority of the primary control system and secondary system(s), if provided, specified in percent of power or thrust output. This essentially requires the manufacturer to state the control parameters to which the system is designed so that evaluation of the software design methodology may be made and the need for dedicated power sources may be established. This proposal does not require manufacturers to perform any additional testing or activities beyond current certification practices.
Proposal 2 requires that electrical or electronic control systems must be designed and constructed so that any failure of aircraft supplied power or data will not result in an excessive change of power or thrust or prevent continued safe operation of the engine. This proposal provides the engine manufacturer with alternatives in order to meet this requirement. For example, the manufacturer may meet the requirement through supply of an independent power supply such as a generator, or through a secondary power supply such as batteries, if the above conditions can be proved and documented. Establishing the certification requirement through the latter alternative may be difficult given present state-of-the-art technology. Regardless, the FAA has strictly interpreted this certification issue in the existing FAR as requiring engine isolation.
Proposal 3 requires that electrical or electronic control systems be designed and constructed so that any probable failure or malfunction of electrical or electronic components will not prevent continued safe operation of the engine. All manufacturers have chosen in the past to design and construct a hydromechanical or electronic control backup system that accomplishes this objective, and the FAA has approved these methods. Therefore, this requirement codifies current practices.
Proposal 4 requires that electrical or electronic control systems have environmental limits, including transients due to lightning strikes, specified. As with current certification practice, the requirement that the aircraft withstand lightning transients and continue operation, remains.
Proposal 5 requires that electrical or electronic control systems have all associated software designed and implemented to prevent errors which would result in an excessive loss of power or thrust or unsafe conditions, and have the method used to design and implement the software specified and be suitable for application. Software components are generally designed to critical levels. This proposed rule would provide the flexibility to allow the design of certain software components to less than critical levels if the manufacturer can show that unsafe conditions would not result from it.
Therefore, the proposed rule will establish clearer functional objective requirements that provide the basis for the certification of engine control systems. Furthermore, codifying these functional requirements will provide unquantified benefits to manufacturers and the Federal government by allowing them to standardize their certification efforts, thus resulting in reduced design, testing, and administrative costs.
This regulatory action merely proposes to codify and standardize in Part 33 Subpart B, functional requirements (objectives) pertaining to the certification of electrical and electronic engine control systems. This proposed rule is in consonance with present certification requirements as pertains to engine control systems and does not mandate specific design requirements. Because this proposed rule would not impose certification standards (objective) beyond those currently applied in practice by the FAA, there is no cost impact associated with the proposal. Furthermore, as described above, this proposed rule provides benefits to manufacturers and the Federal government through standardization of certification efforts. The FAA invites comments on the benefit and cost aspects of this proposed rule.
Trade Impact
The FAA cannot discern what impact, if any, this regulation would have on foreign trade. FAA invites comments on what impact this regulation would have on the sale of foreign aviation products or services in the U.S. and on the sale of U.S. aviation products and services in foreign countries.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) was enacted by Congress to insure, among other things, that small entities are not disproportionately affected by government regulations. The RFA requires agencies to review rules which may have a "significant economic impact on a substantial number of small entities". There are no known engine manufacturers, airframe manufacturers, or manufacturers of electrical or electronic engine control systems which are considered to be "small entities" under the definitions of the RFA. Therefore, under the criteria of the RFA, it is certified that this proposal will not have a significant economic impact on a substantial number of small entities.
Conclusion
The FAA has determined that this is not a major regulation under Executive Order 12291. Its adoption will result in savings to the private sector, to consumers, and to the governmental sector by lowering design, testing, and administrative costs incurred in the type certification of aircraft and engines. In addition, the FAA has determined that this amendment is not significant under the Department of Transportation Regulatory Policies and Procedures (44 FR 11034; February 26, 1979). The evaluation prepared for this action is contained in the regulatory docket. A copy of it may be obtained by contacting the person identified under the caption "FOR FURTHER INFORMATION CONTACT".
List of Subjects in 14 CFR Part 33
Aircraft engines, Aircraft aviation safety.
Regulatory Information
The Proposed Amendment
Accordingly, the FAA proposes to amend Part 33 of the FAR (14 CFR Part 33) as follows:
PART 33 - AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES
By adding new Sec. 33.XX to read as follows:
Sec. 33.XX Electronic engine control systems.
Each control system which relies on electrical or electronic means for operation must:
(a) Have the degree of authority of the primary control system and secondary systems(s), if provided, specified in percent of power or thrust output for normal operation and failure conditions.
(b) Be designed and constructed so that any failure of aircraft supplied power or data will no result in a significant change of power or thrust or prevent continued safe operation of the engine.
(c) Be designed and constructed so that any probable failure or malfunction of electrical or electronic components of the control will not result in an unsafe condition or loss of ability to control the engine over an approved range of power or thrust.
(d) Have environmental limits, including transients due to lightning strikes, specified.
(e) Have all associated software designed and implemented to prevent errors which would result in an excessive loss of power or thrust or other unsafe condition, and have the method used to design and implement the software specified and be suitable for the applications.
(Sec. 313(a), 601, and 603, Federal Aviation Act of 1958, as amended (49 U.S.C. 1354a), 1421, and 1423); (49 U.S.C. 106(g) revised, Pub. L. 97-449, January 12, 1983); 14 CFR 11.45)
Footer Information
Issued in Burlington, Massachusetts, on December 21, 1984.
Robert E. Whittington,
Director, New England Region.
[FR Doc. 85-3733 Filed 2-13-85; 8:45 am]
BILLING CODE 4910-13-M
 Comments
Document History
Other Notice of Proposed Rulemaking Actions:
Not Applicable.
Final Rule Actions:
Final Rule. Docket No. 24466; Issued on 05/11/93.
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