[Federal Register Volume 63, Number 92 (Wednesday, May 13, 1998)]
[Rules and Regulations]
[Pages 26422-26424]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-12710]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Parts 21 and 27
[Docket No. SW003; Special Conditions No. 27-003-SC]
Special Conditions: Eurocopter Model AS-355 E, F, F1, F2, N
``Ecureuil II/Twinstar'' Helicopters, Electronic Flight Instruments
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special condition; request for comments.
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SUMMARY: This special condition is issued for the Eurocopter Model AS-
355 E, F, F1, F2, N ``Ecureuil II/Twinstar'' helicopters. These
helicopters will have a novel or unusual design feature associated with
the Electronic Flight Instruments. The applicable airworthiness
regulations do not contain adequate or appropriate safety standards to
protect systems that perform critical control functions, or provide
critical displays, from the effects of high-intensity radiated fields
(HIRF). This special condition contains the additional safety standards
that the Administrator considers necessary to ensure that critical
functions of systems will be maintained when exposed to HIRF.
DATES: The effective date of this special condition is April 30, 1998.
Comments must be received on or before July 13, 1998.
ADDRESSES: Comments on this special condition may be mailed in
duplicate to: Federal Aviation Administration, Office of the Regional
Counsel, Attention: Rules Docket No. SW003, Fort Worth, Texas 76193-
0007 or deliver in duplicate to the Office of the Regional Counsel at
2601 Meacham Blvd., Fort Worth, Texas 76137. Comments must be marked:
Rules Docket No. SW003. Comments may be inspected in the Rules Docket
weekdays, except Federal holidays, between 8:30 a.m. and 4:00 p.m.
FOR FURTHER INFORMATION CONTACT: Robert McCallister, FAA, Rotorcraft
Directorate, Regulations Group, Fort Worth, Texas 76193-0111; telephone
817-222-5121, fax 817-222-5961.
SUPPLEMENTARY INFORMATION: The FAA has determined that notice and
opportunity for prior public comment hereon are impracticable because
these procedures would significantly delay issuance of the approval
design and thus delivery of the affected aircraft. In addition, notice
and opportunity for prior public comment are unnecessary since the
substance of this special condition has been subject to the public
comment process in several prior instances with no substantive comments
received. The FAA therefore finds that good cause exists for making
this special condition effective upon issuance.
Comments Invited
Interested persons are invited to submit such written data, views,
or arguments as they may desire. Communications should identify the
regulatory docket or special condition 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 by the
Administrator. The special condition may be changed in light of the
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. Commenters wishing the FAA to acknowledge receipt of their
comments submitted in response to this special condition must include a
self-addressed, stamped postcard on which the following statement is
made: ``Comments to Rules Docket No. SW003.'' The postcard will be date
stamped and returned to the commenter.
Background
On February 25, 1998, American Eurocopter announced their intent to
amend, under their Designated Airworthiness Authority (DAS), the
Supplemental Type Certificate (STC) SH7714AW-D to add electronic flight
instruments, including an Attitude Display Instrument. This amendment
and the original STC are effective for the Models AS-355 E, F, F1, F2,
N ``Ecureuil II/Twinstar'' helicopters. These are normal category five-
passenger helicopters powered by two Allison 250-C20 engines for the
Model AS-355 E, F, F1, F2 helicopters and by two Turbomeca Arrius 1A
engines for the Model AS-355 N helicopters.
Type Certification Basis
Under the provisions of 14 CFR 21.101, Eurocopter must show that
the Model AS-355 E, F, F1, F2, N ``Ecureuil II/Twinstar'' helicopters
meet the applicable provisions of the regulations incorporated by
reference in Type Certificate Data Sheet (TCDS) No. H11EU or the
applicable regulations in effect on the date of notification of intent
to change the Models AS-355 E, F, F1, F2, N. The regulations
incorporated by reference in the type certificate are commonly referred
to as the ``original type certification basis.'' The regulations
incorporated by reference in H11EU are as follows: Sec. 21.29 and, for
Models AS-355 E, F, F1, F2, 14 CFR part 27, effective February 1, 1965
plus Amendments 27-1 through 27-16; for Model AS-355 N, part 27,
effective February 1, 1965, plus Amendments 27-1 through 27-20, and the
following sections of Amendment 27-1: 27.21, 27.45, 27.71, 27.79,
27.143, 27.151, 27.161, 27.173, 27.175, 27.177, 27.672, 27.673, 27.729,
27.735, 27.779, 27.807, 27.1329, 27.1413, 27.1519, 27.1525, 27.1555,
27.1585, and 27.1587. In addition, the certification basis includes
certain other special conditions.
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.
[[Page 26423]]
In addition to the applicable airworthiness regulations and special
conditions, the Models AS-355 E, F, F1, F2, N must comply with the
noise certification requirements of 14 CFR part 36; and the FAA must
issue a finding of regulatory adequacy pursuant to section 611 of
Public Law 92-574, the ``Noise Control Act of 1972.''
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49, 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).
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).
Novel or Unusual Design Features
The Eurocopter Model AS-355 E, F, F1, F2, N ``Ecureuil II/
Twinstar'' helicopters will incorporate the following novel or unusual
design features: Electrical, electronic, or combination of electrical
electronic (electrical/electronic) systems, such as electronic flight
instruments, that will be providing displays critical to the continued
safe flight and landing of the helicopter. Electronic flight
instruments provide information critical for operation in instrument
meteorological conditions.
Discussion
The Eurocopter Model AS-355 E, F, F1, F2, N ``Ecureuil II/
Twinstar'' helicopters, at the time of application, were identified as
having modifications that incorporate one and possibly more electrical/
electronic systems, such as electronic flight instruments. After the
design is finalized, Eurocopter will provide the FAA with a preliminary
hazard analysis that will identify any other critical functions,
required for safe flight and landing, performed by the electrical/
electronic systems.
Recent advances in technology have given rise to the application in
aircraft designs of advanced electrical/electronic systems that perform
critical control functions, or provide critical displays. These
advanced systems respond to the transient effects of induced electrical
current and voltage caused by HIRF incident on the external surface of
the helicopter. 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.
Furthermore, the electromagnetic environment has undergone a
transformation not envisioned by the current application of
Sec. 27.1309(a). Higher energy levels radiate from operational
transmitters currently used for radar, radio, and television. Also, 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 the technological advances in helicopter
design and the changing environment have resulted in an increased level
of vulnerability of the electrical/electronic systems required for the
continued safe flight and landing of the helicopter. 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 the developments in technology and environment and, in
1986, initiated a high priority program to (1) determine and define
electromagnetic energy levels; (2) develop and describe 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 two levels of the HIRF environment that a helicopter could
be exposed to, one environment for Visual Flight Rules (VFR) operations
and a different environment for Instrument Flight Rules (IFR)
operations. While the HIRF rulemaking requirements are being finalized,
the FAA is adopting a special condition for the certification of
aircraft that employ electrical/electronic systems that perform
critical control functions, or provides critical displays. 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 to
be protected from these energy levels. These external threat levels are
believed to represent the exposure for a helicopter operating under VFR
or IFR.
Compliance with HIRF requirements will be demonstrated by tests,
analysis, models, similarity with existing systems, or a combination of
these methods. 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.
This special condition will require the systems that perform
critical control functions, or provide critical displays, as installed
in the aircraft, to meet certain standards based on either a defined
HIRF environment or a fixed value using laboratory tests. Control
system failures and malfunctions can more directly and abruptly
contribute to a catastrophic event than display system failures and
malfunctions. Therefore, it is considered appropriate to require more
rigorous HIRF verification methods for critical control systems than
for critical display systems.
The applicant may demonstrate that the operation and operational
capabilities of the installed electrical/electronic systems that
perform critical functions are not adversely affected when the aircraft
is exposed to the defined HIRF test environment. The FAA has determined
that the test environment defined in Table 1 is acceptable for critical
control functions in helicopters. The test environment defined in Table
2 is acceptable for critical display systems in helicopters.
The applicant may also demonstrate by a laboratory test that the
electrical/electronic systems that perform critical control functions
or provide critical displays 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
[[Page 26424]]
compliance with the defined HIRF environment, no credit will be given
for signal attenuation due to installation. A level of 100 volts per
meter (v/m) is appropriate for critical display systems. A level of 200
v/m is appropriate for critical control functions. Laboratory test
levels are defined according to RTCA/DO-160D Section 20 Category W (100
v/m and 150 mA) and Category Y (200 v/m and 300 mA). As defined in DO-
160D Section 20, the test levels are defined as the peak of the root
means squared (rms) envelope. As a minimum, the modulations required
for RTCA/DO-160D Section 20 Categories W and Y will be used. Other
modulations should be selected as the signal most likely to disrupt the
operation of the system under test, based on its design
characteristics. 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 400 MHz and 1 KHz
square wave with greater than 90 percent depth of modulation from 400
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.
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 an unsafe 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 display 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, including control and
display.
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.--VFR Rotorcraft, Field Strength Volts/Meter
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Frequency Peak Average
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10-100 KHz........................................ 150 150
100-500........................................... 200 200
500-2000.......................................... 200 200
2-30 MHz.......................................... 200 200
30-100............................................ 200 200
100-200........................................... 200 200
200-400........................................... 200 200
400-700........................................... 730 200
700-1000.......................................... 1400 240
1-2 GHz........................................... 5000 250
2-4............................................... 6000 490
4-6............................................... 7200 400
6-8............................................... 1100 170
8-12.............................................. 5000 330
12-18............................................. 2000 330
18-40............................................. 1000 420
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Table 2.--IFR Rotorcraft Field Strength Volts/Meter
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Frequency Peak Average
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10-100 KHz........................................ 50 50
100-500........................................... 50 50
500-2000.......................................... 50 50
2-30 MHz.......................................... 100 100
30-70............................................. 50 50
70-100............................................ 50 50
100-200........................................... 100 100
200-400........................................... 100 100
400-700........................................... 700 50
700-1000.......................................... 700 100
1-2 GHz........................................... 2000 200
2-4............................................... 3000 200
4-6............................................... 3000 200
6-8............................................... 1000 200
8-12.............................................. 3000 300
12-18............................................. 2000 200
18-40............................................. 600 200
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Applicability
As previously discussed, this special condition is applicable to
the Model AS-355 E, F, F1, F2, N helicopters. Should American
Eurocopter 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 condition would apply to that model as well under
the provisions of Sec. 21.101(a)(1).
Conclusion
This action affects only certain novel or unusual design features
on one model series of helicopter. It is not a rule of general
applicability and affects only the applicant who applied to the FAA for
approval of these features on the helicopter.
The substance of this special condition has been subjected to the
notice and comment period in several prior instances and has been
derived without substantive change from those previously issued. It is
unlikely that prior public comment would result in a significant change
from the substance contained herein. For this reason and because a
delay would significantly affect the certification of the helicopter,
which is imminent, the FAA has determined that prior public notice and
comment are unnecessary and impracticable, and good cause exists for
adopting this special condition upon issuance. The FAA is requesting
comments to allow interested persons to submit views that may not have
been submitted in response to the prior opportunities for comment
described above.
List of Subjects in 14 CFR Parts 21 and 27
Aircraft, Air transportation, Aviation safety, Rotorcraft, Safety.
The authority citation for these special conditions is as follows:
42 U.S.C. 7572; 49 U.S.C. 106(g), 40105, 40113, 44701-44702, 44704,
44709, 44711, 44713, 44715, 45303.
The Special Condition
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special condition is issued as part of the
type certification basis for Eurocopter Models AS 355 E, F, F1, F2, N
``Ecureuil II/Twinstar'' helicopters.
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 helicopter
is exposed to high intensity radiated fields external to the
helicopter.
Issued in Fort Worth, Texas, on April 30, 1998.
Eric Bries,
Acting Manager, Rotorcraft Directorate Aircraft Certification Service,
ASW-100.
[FR Doc. 98-12710 Filed 5-12-98; 8:45 am]
BILLING CODE 4910-13-U
