Special Conditions; Hamilton Standard Model 247F Propeller

[Federal Register Volume 60, Number 228 (Tuesday, November 28, 1995)] [Rules and Regulations] [Pages 58508-58509] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 95-28995]

======================================================================= -----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 35

[Docket No. 94-ANE-50; Notice No. 35-ANE-01]

Special Conditions; Hamilton Standard Model 247F Propeller

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

-----------------------------------------------------------------------

SUMMARY: These special conditions are issued for Hamilton Standard Model 247F 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 the 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: December 28, 1995.

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 March 8, 1993, Hamilton Standard applied for an amendment to the type certificate of Model 247F 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 normally 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 247F propeller. This control is designed to operate with existing mechanical and hydraulic interface of the engine and propeller. Electronic propeller and pitch controls introduce potential failures that can result in unsafe conditions. These types of failures are not addressed by the requirements of part 35. These failures can lead to the following possible unsafe 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.

[[Page 58509]]

Certification issues that must be addressed are possible loss of aircraft-supplied electrical power, aircraft supplied data, failures modes, environmental effects including lightning strikes and 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 247F 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 247F 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 247F 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 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).

Novel or Unusual Design Features

Because of the unusual design features of the Hamilton Standard Model 247F propeller with electronic propeller and pitch control, the FAA issues special conditions under Sec. 21.16 of the FAR. 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 was concerned that the terms ``unsafe conditions'' and ``unacceptable change'' are vague and could lead to multiple interpretations if the terms were not defined in the special conditions. The FAA agrees, and the term ``unsafe conditions'' is now defined in the special conditions and the term ``unacceptable change'' has been removed and replaced with the term ``unsafe condition''. One commenter was concerned with system redundancy and stated that FAR 25.1309, its associated Advisory Circular and a Failure Modes Effects Analysis (FMEA) should be applied to the special condition. The FAA disagrees. The special condition as stated in paragraph (a)(2) addresses the commenter's concern 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 an unsafe condition. Also, the propeller manufacturer includes a 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. 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 Hamilton Standard Model 247F 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 aircraft. 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; and 14 CFR 11.49 and 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 247F propeller and pitch control system. Considering that electronic propeller and pitch control systems introduce potential failures that can result in unsafe 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 an unsafe condition of the 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 of the propeller control system, result in an unsafe 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 an unsafe propeller pitch setting or an unsafe condition. (5) Be designed and constructed so that a failure or malfunction of electrical or electronic components in the propeller or control system will not prevent safe operation of any remaining propeller that is installed on the aircraft. (b) For the purpose of these special conditions, an unsafe 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 November 16, 1995. Jay Pardee, Manager, Engine and Propeller Directorate, Aircraft Certification Service. [FR Doc. 95-28995 Filed 11-27-95; 8:45 am] BILLING CODE 4910-13-M