[Federal Register Volume 61, Number 3 (Thursday, January 4, 1996)]
[Rules and Regulations]
[Pages 254-255]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-56]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 35
[Docket No. 94-ANE-61; Special Condition No. 35-ANE-03]
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 Hamilton Standard
Model 568F propeller. This propeller is constructed using all composite
blades, a novel and unusual design feature. Part 35 of the Federal
Aviation Regulations (FAR's) currently does not address the
airworthiness considerations associated with propellers constructed
using all composite blades. These special conditions contain additional
safety standards which the Administrator finds necessary to establish a
level of safety equivalent to that established by the airworthiness
standards of part 35 of the FAR's.
EFFECTIVE DATE: February 5, 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. This propeller is
constructed using all composite blades, a novel and unusual design
feature. A Notice of Proposed Special Conditions was published in the
Federal Register on January 20, 1995 (60 FR 4116) for the Hamilton
Standard Model 568F propeller constructed with composite material.
Propellers constructed entirely of composite material have additional
airworthiness considerations not currently addressed by part 35 of the
Federal Aviation Regulations (FAR). Those additional airworthiness
considerations associated with propellers constructed using all
composite blades are propeller integrity following a bird strike,
propeller integrity following a lightning strike, and propeller fatigue
strength when exposed to the deteriorating effects of in-service use
and the environment.
Type Certificate Basis
Under the provisions of Sec. 21.17 of the FAR's, 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 because it is
constructed using composite material. Therefore, the Administrator
prescribes special conditions under the provisions of Sec. 21.16 of the
FAR's 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).
Novel or Unusual Design Features
Hamilton Standard Model 568F propeller incorporates propeller
blades constructed using composite material. This material has fibers
that are woven or aligned in specific directions to give the material
directional strength properties. These properties depend on the type of
fiber, the orientation and concentration of fiber, and matrix material.
Composite materials could exhibit multiple modes of failure. Propellers
constructed of composite material must demonstrate airworthiness when
considering these novel design features.
The requirements of part 35 of the FAR's were established to
address the airworthiness considerations associated with wood and metal
propellers used primarily on reciprocating engines. Propeller blades of
this type are generally thicker than composite blades, and have
demonstrated good service experience following a bird strike. Propeller
blades constructed using composite material are generally thinner when
used on turbine engines, and are typically installed on high
performance aircraft. High performance aircraft generally fly at high
airspeeds with correspondingly high impact forces associated with a
bird strike. Thus, composite propellers must demonstrate propeller
integrity following a bird strike.
In addition, part 35 of the FAR's do not currently require a
demonstration of propeller integrity following a lightning strike. No
safety considerations arise from lightning strikes on propellers
constructed of metal because the electrical current is safely conducted
through the metal blade without damage to the propeller. Fixed pitched,
wooden propellers are generally used on engines installed on small,
general aviation aircraft that typically do not encounter flying
conditions conducive to lightning strikes. Composite propeller blades,
however, may be used on turbine engines and high performance aircraft
which have an increased risk of lightning strikes. Composite blades may
not safely conduct or dissipate the electrical current from a lightning
strike. Severe damage can result if the propellers are not properly
protected. Therefore, composite blades must demonstrate propeller
integrity following a lightning strike. Information on testing for
lightning protection is set out in SAE Report AE4L, entitled,
``Lightning Test Waveforms and Techniques for Aerospace Vehicles and
Hardware,'' dated June 20, 1978.
Lastly, the current certification requirements address fatigue
evaluation only of metal propeller blades or hubs, and those metal
components of non-metallic blade assemblies. Allowable design stress
limits for composite blades must consider the deteriorating effects of
the environment and in-service use, particularly those effects from
temperature, moisture, erosion and chemical attack. Composite blades
also present new and different considerations for retention of the
blades in the propeller hub.
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 comments received.
One commenter is concerned that the terms ``reasonable and
foreseeable'' in paragraph (3) FATIGUE EVALUATION of the special
condition is a vague interpretation, and will result in large variation
in how this requirement is applied.
The FAA disagrees. The special conditions are written with the
accepted terminology from Sec. 35.37, Fatigue limit tests, of the
FAR's, which states that ``The fatigue evaluation must include
consideration of all reasonably foreseeable vibration load patterns.''
This terminology has been established because each propeller
installation presents a unique set of operating conditions that must be
incorporated
[[Page 255]]
into the fatigue evaluation. The inclusion of specific aircraft
operating conditions may result in the fatigue evaluation of operating
conditions of minor significance while leaving out conditions of major
significance.
One commenter agreed with the three proposed special conditions as
written and proposed two additional special conditions concerning ice
strikes due to ice shedding from the airframe and ice accretion due to
the heat transfer properties of composite materials.
The FAA disagrees with the addition of the two additional special
conditions for the following reasons. First, ice strikes due to ice
shedding from the airframe is a concern for pusher type installations.
The Hamilton Standard Model 568F propeller is a tractor configuration
and therefore normally will not be exposed to ice shedding from the
airframe. Second, heat transfer properties of the Hamilton Standard
Model 568F composite blade are similar to other composite shell and all
composite blades with deicing systems that have had a good service
history. In addition for propeller installations that require deicing,
the propeller manufacture provides a deicing system and the required
documentation to the airframer for compliance with the current
regulations.
Conclusion
This action affects only the Hamilton Standard Model 568F propeller
and future propeller models within this series. It is not a rule of
general application, and it affects only the manufacturer who applied
to the FAA for approval of this propeller model.
List of Subjects in 14 CFR Part 35
Air Transportation, Aircraft, Aviation safety, Safety.
PART 35--[AMENDED]
The authority citation 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
Administrator, the Federal Aviation Administration (FAA) issues the
following special conditions for the Hamilton Standard Model 568F
Propeller:
(a) For purposes of these special conditions, a hazardous condition
is considered to exist for each of the following conditions:
(1) Loss of the propeller blade, or a major portion of a blade.
(2) Overspeed of the propellers.
(3) Unintended movement of the blade below the established minimum
inflight blade angle, or to an angle that results in excessive drag.
(4) The inability to feather the propeller when necessary.
(b) In addition to the requirements of Federal Aviation Regulation
part 35, the following must be shown:
(1) BIRD STRIKE
For propeller of composite construction it must be shown that:
The propeller can withstand a 4 pound bird strike at the blade's
critical radial location when operating at takeoff RPM and liftoff (Vr)
speed of a typical aircraft, without giving rise to a hazardous
condition and while maintaining the capability to be feathered.
(2) LIGHTNING STRIKE
A lightning strike on a propeller of a composite construction shall
not result in a hazardous condition. The propeller shall be capable of
continued safe operation.
(3) FATIGUE EVALUATION
A fatigue evaluation must be provided and the fatigue limits
determined for each propeller hub, blade, and each primary load
carrying component of the propeller. The fatigue evaluation must
consider all known and reasonable foreseeable vibration and cyclic load
patterns that may be encountered in service. The fatigue limits must
account for the effects of in-service deterioration, such as impact
damage, nicks, grooves, galling, or bearing wear; for variations in
production material properties; for environmental effects such as
temperature, moisture, erosion, chemical attack, etc., that cause
deterioration.
Issued in Burlington, Massachusetts, on December 19, 1995.
James C. Jones,
Acting Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. 96-56 Filed 1-3-96; 8:45 am]
BILLING CODE 4910-13-M
