[Federal Register Volume 61, Number 90 (Wednesday, May 8, 1996)]
[Proposed Rules]
[Pages 20760-20762]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-11496]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
[Docket No. 96-ASW-2; Notice No. SC-96-2-SW]
Special Condition: Sikorsky Model S76C, High Intensity Radiated
Fields
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed special condition.
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SUMMARY: This notice proposes a special condition for the Sikorsky
Model S76C helicopter. This helicopter will have a novel or unusual
design feature associated with the installation of electronic systems
that perform critical functions. The applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
the protection of electronic systems that perform critical functions
from the effects of external high intensity radiated fields (HIRF).
This notice contains the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the applicable airworthiness
standards.
DATES: Comments must be received on or before June 7, 1996.
ADDRESSES: Comments on this proposal may be mailed in duplicate to the
Federal Aviation Administration (FAA), Office of the Assistant Chief
Counsel, Attn: Rules Docket No. 96-ASW-2, Fort Worth, Texas 76193-0007,
or delivered in duplicate to the Office of the Assistant Chief Counsel,
2601 Meacham Blvd., Fort Worth, Texas. Comments must be marked Docket
No. 96-ASW-2. Comments may be inspected in the Rules Docket weekdays,
except Federal holidays, between 9 a.m. and 3 p.m.
FOR FURTHER INFORMATION CONTACT:
Mr. Robert McCallister, FAA, Rotorcraft Directorate, Regulations Group,
Fort Worth, Texas 76193-0110; telephone (817) 222-5121.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of this
proposed special condition by submitting such written data, views, or
arguments as they may desire. Communications should identify the
regulatory docket number and be submitted in duplicate to the address
specified above. All communications received on or before the closing
date for comments will be considered before taking action on this
proposal. The special condition proposed in this notice may be changed
in light of comments received. All comments received will be available
in the Rules Docket for examination by interested persons, both before
and after the closing date for comments. A report summarizing each
substantive public contact with FAA personnel concerning this
rulemaking will be filed in the docket. Persons wishing the FAA to
acknowledge receipt of their comments submitted in response to this
notice must submit with those comments a self-addressed, stamped
postcard on which the following statement is made: ``Comments to Docket
No. 96-ASW-2.'' The postcard will be date and time stamped and returned
to the commenter.
Background
Sikorsky Aircraft Corporation, Stratford, Connecticut, applied for
an amendment to the Type Certificate for Model S76C helicopter on
August 15, 1990. The amendment will allow installation of Turbomeca
Arriel Model 2S1 engines with FADEC control and 30 second/2 minute
ratings as alternate engines for the Sikorsky Model S76C helicopter.
This is a 12 (14 including crew) passenger, twin engine, 11,700 pound
transport category helicopter.
Type Certificate Basis
The type certification basis is 14 Code of Federal Regulations part
29, February 1, 1965, and Amendments 29-1 through 29-11; in addition,
portions of Amendment 29-12, specifically, Secs. 29.67, 29.71, 29.75,
29.141, 29.173, 29.175, 29.931, 29.1189(a)(2), 29.1555(c)(2),
29.1557(c); Amendment 29-13, specifically Sec. 29.965; Amendment 29-24,
specifically Sec. 29.1325; Amendment 29-30 specifically Sec. 29.811;
Amendment 29-34, specifically Secs. 29.67(a)(1)(i), 29.923(a), (b) (1)
& (3), 29.1143(f), 29.1305(a) (24) & (25), 29.1521 (i) & (j) and
29.1549(e); and Amendment 36-14 of 14 CFR part 36, Appendix H.
If the Administrator finds that the applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
these helicopters because of a novel or unusual design feature, special
conditions are prescribed 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
Federal Aviation Administration Sec. 11.49 after public notice, as
required by Secs. 11.28 and 11.29(b), and become part of the type
certification basis in accordance with Federal Aviation Administration
21.101(b)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design feature, the special conditions would also apply to the
other model under the provisions of Sec. 21.101(a)(1).
Discussion
The Sikorsky Model S76C helicopter, at the time of the application
for amendment to U.S. Type Certificate
[[Page 20761]]
H1NE, was identified as incorporating one and possibly more electrical,
electronic, or combination of electrical and electronic (electrical/
electronic) systems that will perform functions critical to the
continued safe flight and landing of the helicopters. A Full Authority
Digital Engine Control (FADEC) is an example of an electronic device
that performs the critical functions of engine control. The control of
the engines is critical to the continued safe flight and landing of the
helicopter during visual flight rules (VFR) and instrument flight rules
(IFR) operations.
If it is determined that this helicopter currently or at a future
date incorporates other electrical/electronic systems performing
critical functions, those systems also will be required to comply with
the requirements of this special condition.
Recent advances in technology have prompted the design of aircraft
that include advanced electrical and electronic systems that perform
functions required for continued safe flight and landing. However,
these advanced systems respond to the transient effects of induced
electrical current and voltage caused by the HIRF incident on the
external surface of the helicopters. These induced transient currents
and voltages can degrade the performance of the electrical/electronic
systems by damaging the components or by upsetting the systems'
functions.
Futhermore, the electromagnetic environment has undergone a
transformation not envisioned by the current application of
Sec. 29.1309(a). Higher energy levels radiate from operational
transmitters currently used for radar, radio, and television; the
number of transmitters has increased significantly.
Existing aircraft certification requirements are inappropriate in
view of these technological advances. In addition, the FAA has received
reports of some significant safety incidents and accidents involving
military aircraft equipped with advanced electrical/electronic systems
when they were exposed to electromagnetic radiation.
The combined effects of technological advances in helicopter design
and the changing environment have resulted in an increased level of
vulnerability of the electrical and electronic systems required for the
continued safe flight and landing of the helicopters. Effective
measures to protect these helicopters against the adverse effects of
exposure to HIRF will be provided by the design and installation of
these systems. The following primary factors contributed to the current
conditions: (1) increased use of sensitive electronics that perform
critical functions, (2) reduced electromagnetic shielding afforded
helicopter systems by advanced technology airframe materials, (3)
adverse service experience of military aircraft using these
technologies, and (4) an increase in the number and power of radio
frequency emitters and the expected increase in the future.
The FAA recognizes the need for aircraft certification standards to
keep pace with technological developments and a changing environment
and, in 1986, initiated a high priority program to (1) determine and
define electromagnetic energy levels; (2) develop guidance material for
design, test, and analysis; and (3) prescribe and promulgate regulatory
standards. The FAA participated with industry and airworthiness
authorities of other countries to develop internationally recognized
standards for certification.
The FAA and airworthiness authorities of other countries have
identified a level of HIRF environment that a helicopter could be
exposed to during IFR operations. While the HIRF requirements are being
finalized, the FAA is adopting a special condition for the
certification of aircraft that employ electrical/electronic systems
that perform critical functions. The accepted maximum energy levels
that civilian helicopter system installations must withstand for safe
operation are based on surveys and analysis of existing radio frequency
emitters. This special condition will require the helicopters'
electrical/electronic systems and associated wiring be protected from
these energy levels. These external threat levels are believed to
represent the worst-case exposure for a helicopter operating under IFR.
The HIRF environment specified in this proposed special condition
is based on many critical assumptions. With the exception of takeoff
and landing at an airport, one of these assumptions is the aircraft
would be not less than 500 feet above ground level (AGL). Helicopters
operating under visual flight rules (VFR) routinely operate at less
than 500 feet AGL and perform takeoffs and landings at locations other
than controlled airports. Therefore, it would be expected that the HIRF
environment experienced by a helicopter operating VFR may exceed the
defined environment by 100 percent or more.
This special condition will require the systems that perform
critical functions, as installed in the aircraft, to meet certain
standards based on either a defined HIRF environment or a fixed value
using laboratory tests.
The applicant may demonstrate that the operation and operational
capability of the installed electrical/electronic systems that perform
critical functions are not adversely affected when the aircraft is
exposed to the defined HIRF environment. The FAA has determined that
the environment defined in Table 1 is acceptable for critical functions
in helicopters operating at or above 500 feet AGL. For critical
functions of helicopters operating at less than 500 feet AGL,
additional factors must be considered.
The applicant may also demonstrate by a laboratory test that the
electrical/electronic systems that perform critical functions can
withstand a peak electromagnetic field strength in a frequency range of
10 KHZ to 18 GHZ. If a laboratory test is used to show
compliance with the defined HIRF environment, no credit will be given
for signal attenuation due to installation. A level of 100 v/m and
other considerations, such as an alternate technology backup that is
immune to HIRF, are appropriate for critical functions during IFR
operations. A level of 200 v/m and further considerations, such as an
alternate technology backup that is immune to HIRF, are more
appropriate for critical functions during VFR operations.
Applicants must perform a preliminary hazard analysis to identify
electrical/electronic systems that perform critical functions. The term
``critical'' means those functions whose failure would contribute to or
cause a failure condition that would prevent the continued safe flight
and landing of the helicopters. The systems identified by the hazard
analysis as performing critical functions are required to have HIRF
protection.
A system may perform both critical and noncritical functions.
Primary electronic flight systems and their associated components
perform critical functions such as attitude, altitude, and airspeed
indications. HIRF requirements would apply only to the systems that
perform critical functions.
Compliance with HIRF requirements will be demonstrated by tests,
analysis, models, similarity with existing systems, or a combination of
these methods. The two basic options of either testing the rotorcraft
to the defined environment or laboratory testing may not be combined.
The laboratory test allows some frequency areas to be under tested and
requires other areas to have some safety margin when compared to the
defined environment. The areas required to have some safety margin are
those that have been, by past testing, shown to exhibit
[[Page 20762]]
greater susceptibility to adverse effects from HIRF; and laboratory
tests, in general, do not accurately represent the aircraft
installation. Service experience alone will not be acceptable since
such experience in normal flight operations may not include an exposure
to HIRF. Reliance on a system with similar design features for
redundancy, as a means of protection against the effects of external
HIRF, is generally insufficient because all elements of a redundant
system are likely to be concurrently exposed to the radiated fields.
The modulation that represents the signal most likely to disrupt
the operation of the system under test, based on its design
characteristics, should be selected. For example, flight control
systems may be susceptible to 3 HZ square wave modulation while
the video signals for electronic display systems may be susceptible to
400 HZ sinusoidal modulation. If the worst-case modulation is
unknown or cannot be determined, default modulations may be used.
Suggested default values are a 1 KHZ sine wave with 80 percent
depth of modulation in the frequency range from 10 KHZ to 500
MHZ and 1 KHZ square wave with greater than 90 percent depth
of modulation from MHZ to 18 GHZ. For frequencies where the
unmodulated signal would cause deviations from normal operation,
several different modulating signals with various waveforms and
frequencies should be applied.
Acceptable system performance would be attained by demonstrating
that the critical function components of the system under consideration
continue to perform their intended function during and after exposure
to required electromagnetic fields. Deviations from system
specifications may be acceptable but must be independently assessed by
the FAA on a case-by-case basis.
Table 1.--Field Strength Volts/meter
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Frequency Peak Average
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10-100 KHZ................ 50 50
100-500................... 60 60
500-2000.................. 70 70
2-30 MHZ.................. 200 200
30-100.................... 30 30
100-200................... 150 33
200-400................... 70 70
400-700................... 4020 935
700-1000.................. 1700 170
1-2 GHZ................... 5000 990
2-4....................... 6680 840
4-6....................... 6850 310
6-8....................... 3600 670
8-12...................... 3500 1270
12-18..................... 3500 360
18-40..................... 2100 750
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As discussed above, these special conditions are applicable
initially to the Sikorsky Model S76C helicopter. Should Sikorsky apply
at a later date for a change to the type certificate to include another
model incorporating the same novel or unusual design feature, the
special conditions would apply to that model as well, under the
provisions of Sec. 21.101(a)(1).
Conclusion
This action affects only certain unusual or novel design features
on one model of helicopter. 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 affected helicopters.
List of Subjects in 14 CFR Parts 21 and 29
Aircraft, Air transportation, Aviation safety, Rotorcraft, Safety.
The authority citation for this special condition is as follows:
Authority: 42 U.S.C. 7572; 49 U.S.C. 106(g), 40105, 40113,
44701, 44702, 44704, 44709, 44711, 44713, 44715, 45303.
The Proposed Special Condition
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration (FAA) proposes the
following special condition as a part of the type certification basis
for the Sikorsky Model S76C helicopter.
Protection for Electrical and Electronic Systems From High Intensity
Radiated Fields
Each system that performs critical functions must be designed and
installed to ensure that the operation and operational capabilities of
these critical functions are not adversely affected when the
helicopters are exposed to high intensity radiated fields external to
the helicopters.
Issued in Fort Worth, Texas, on April 26, 1996.
Larry M. Kelly,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 96-11496 Filed 5-7-96; 8:45 am]
BILLING CODE 4910-13-M
