[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