Special Conditions; Hamilton Standard Model 568F Propeller

[Federal Register Volume 61, Number 2 (Wednesday, January 3, 1996)] [Rules and Regulations] [Pages 114-115] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 96-55]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 35

[Docket No. 94-ANE-60; Special Condition No. 35-ANE-02]

Special Conditions; Hamilton Standard Model 568F Propeller

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Hamilton Standard Model 568F propeller with electronic propeller and pitch control system. The applicable regulations currently do not contain adequate or appropriate safety standards for constant speed propellers with electronic propeller and pitch control. These special conditions contain additional safety standards which the Administrator considers necessary to establish a level of safety equivalent to that established by the airworthiness standards of part 35 of the Federal Aviation Regulations (FAR).

EFFECTIVE DATE: February 2, 1996.

FOR FURTHER INFORMATION CONTACT: Martin Buckman, Engine and Propeller Standards Staff, ANE-110, Engine and Propeller Directorate, Aircraft Certification Service, FAA, New England Region, 12 New England Executive Park, Burlington, Massachusetts, 01803-5229; telephone (617) 238-7112; fax (617) 238- 7199.

SUPPLEMENTARY INFORMATION:

Background

On January 26, 1994, Hamilton Standard applied for type certification for a new Model 568F propeller. The new propeller would use a new electronic propeller and pitch control system in place of the primary governor control and synchrophaser unit. The existing propeller pitch control is monitored by a governor which senses propeller speed and adjusts the pitch to absorb the engine power and therefore maintains the propeller at the correct RPM. When the primary governor fails, the propeller pitch is controlled by an overspeed governor. This type of system is conventional and its airworthiness considerations are addressed by part 35 of the FAR's. The FAA has determined that special conditions are necessary to certificate a Hamilton Standard electronic propeller and pitch control in place of the primary governor control and synchrophaser unit for the Model 568F propeller. A Notice of Proposed Special Conditions was published in the Federal Register on January 20, 1995 (60 FR 4114) for the Hamilton Standard Model 568F propeller with electronic propeller and pitch control system. This control is designed to operate a mechanical and hydraulic interface for the engine and propeller. It commands speed governing, synchrophasing and provides beta scheduling. Electronic propeller and pitch controls introduce potential failures that can result in hazardous conditions. These types of

[[Page 115]] failures are not addressed by the requirements of part 35. These failures can lead to the following possible hazardous conditions: (1) Loss of control of the propeller, (2) Instability of a critical function, (3) Unwanted change in propeller pitch causing improper thrust/ overspeed, and (4) Unwanted action of a critical control function resulting in propeller flat pitch or reverse. Certification issues that must be addressed are possible loss of aircraft-supplied electrical power, aircraft supplied data, failure modes, environmental effects including lightning strike sand high intensity radiated fields (HIRF) and software design. The FAA finds that under the provisions of Sec. 21.16 of the FAR, additional safety standards must be applied to the Hamilton Standard electronic propeller control for Model 568F propellers to demonstrate that it is capable of acceptable operation.

Type Certification Basis

Under the provisions of Sec. 21.17 of the FAR, Hamilton Standard must show that the Model 568F propeller meets the requirements of the applicable regulations in effect on the date of the application. Those FAR's are Sec. 21.21 and part 35, effective February 1, 1965, as amended. The Administrator finds that the applicable airworthiness regulations in part 35, as amended, do not contain adequate or appropriate safety standards for the Model 568F propeller. Therefore, the Administrator prescribes special conditions under the provisions of Sec. 21.16 to establish a level of safety equivalent to that established in the regulations. Special conditions, as appropriate, are issued in accordance with Sec. 11.49 of the FAR's after public notice and opportunity for comment, as required by Secs. 11.28 and 11.29(b), and become part of the type certification basis in accordance with Sec. 21.101(b)(2).

Discussion of Comments

Interested persons have been afforded the opportunity to participate in the making of these special conditions. Due consideration has been given to the comments received. One commenter states concern that the term ``unacceptable change'' is vague and could lead to multiple interpretations if the term was not defined in the special condition. The FAA agrees, and the term ``unacceptable change'' has been removed from the text and replaced with the term ``hazardous'', which is defined in the special condition. The commenter also states concern with system redundancy and states that FAR 25.1309, its associated Advisory Circular and a Failure Modes Effects Analysis should be included in the special conditions. The FAA disagrees. The special condition as written in paragraph (a)(2) addresses the commenter's concerns by requiring that the propeller be designed and constructed so that no single failure or malfunction, or probable combination of failures of electrical or electronic components of the propeller control system, result in a hazardous condition. Also, the propeller manufacturer includes a Failure Modes Effects Analysis (FMEA) report as part of the data required for propeller certification. This same report is submitted to the airframe manufacturer for incorporation into aircraft certification documentation to show compliance with FAR 25.1309. Therefore, the commenter's concerns are already included in the certification documentation and a special condition is not needed. After careful review of the available data, including the comments noted above, the FAA determined that air safety and the public interest require the adoption of these special conditions with the changes discussed previously.

Conclusion

This action affects only the Hamilton Standard Model 568F propeller with a new system of electronic propeller and pitch control. It is not a rule of general applicability and affects only the manufacturer who applied to the FAA for approval of these features on the propeller.

List of Subjects in 14 CFR Part 35

Air transportation, Aircraft, Aviation safety, Safety.

The authority citation for these special conditions continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704; 14 CFR 11.28, 21.16.

The Special Conditions

Accordingly, pursuant to the authority delegated to me by the Federal Aviation Administration (FAA), the following special conditions are issued as part of the type certification basis for the Hamilton Standard Model 568F propeller and pitch control system. Considering that electronic propeller and pitch control systems introduce potential failures that can result in hazardous conditions, the following special conditions are issued. (a) Each propeller and pitch control system which relies on electrical and electronic means for normal operation must: (1) Be designed and constructed so that any failure or malfunction of aircraft-supplied power or data will not result in a hazardous change in propeller pitch setting or prevent continued safe operation of the propeller. (2) Be designed and constructed so that no single failure or malfunction, or probable combination of failures of electrical or electronic components, or mechanical and hydraulic interface of the propeller control system, result in a hazardous condition. (3) Be tested to its environmental limits including transients (variations) caused by lightning and high intensity radiated fields (HIRF) and demonstrate no adverse effects on the control system operation and performance or resultant damage. These tests shall include, but not be limited to, the following: (i) Lightning strikes, such as multiple-stroke and multiple-burst; (ii) Pin-injected tests to appropriate wave forms and levels; (iii) HIRF susceptibility tests. (4) Be demonstrated by analysis/tests that associated software is designed and implemented to prevent errors that would result in a hazardous change in propeller pitch or a hazardous condition. (5) Be designed and constructed so that a failure or malfunction of electrical or electronic components in the propeller control system could not prevent safe operation of any remaining propeller that is installed on the aircraft. (b) For purposes of these special conditions, a hazardous condition is considered to exist for each of the following conditions: (1) Loss of control of the propeller, (2) Instability of a critical function, (3) Unwanted change in propeller pitch causing improper thrust/ overspeed, and (4) Unwanted action of a critical control function resulting in propeller flat pitch or reverse.

Issued in Burlington, Massachusetts, on December 19, 1995. James C. Jones, Acting Manager, Engine and Propeller Directorate, Aircraft Certification Service. [FR Doc. 96-55 Filed 1-2-96; 8:45 am] BILLING CODE 4910-13-M