[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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