[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]



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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.

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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]
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