[Federal Register Volume 64, Number 97 (Thursday, May 20, 1999)]
[Rules and Regulations]
[Pages 27447-27450]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-12743]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 27
[Docket No. SW00S; Special Condition No. 27-00S-SC]
Special Conditions: Bell Helicopter Textron Canada Model 427
Helicopters, High Intensity Radiated Fields
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special condition; request for comments.
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SUMMARY: This special condition is issued for Bell Helicopter Textron
Canada (Bell) Model 427 helicopters. These helicopters 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 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 May 11, 1999.
Comments must be received on or before July 6, 1999.
ADDRESSES: Comments on this special condition may be mailed in
duplicate to: Federal Aviation Administration, Office of the Regional
Counsel, Attention: Rules Docket No. SW00S, 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. SW00S. 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: Jorge Castillo, FAA, Rotorcraft
Directorate, Rotorcraft Standards Staff, Fort Worth, Texas 76193-0110;
telephone 817-222-5127, 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. SW00S.'' The postcard will be date
stamped and returned to the commenter.
Background
On September 16, 1996, Bell applied for a type certificate for the
Model 427 helicopter. The Bell Model 427 helicopter is a 6-passenger (8
including crew) normal category helicopter with a four-bladed rotor. It
is powered by two Pratt and Whitney 206D engines with a gross weight of
6000 pounds.
Type Certification Basis
Under the provisions of 14 CFR 21.17, Bell must show that the Model
427 helicopter meets the applicable provisions of the regulations as
listed below:
14 CFR 21.29
14 CFR Part 27 as amended through and including amendment
27-31 and amendment 27-33
14 CFR Part 29 as amended through and including amendment
29-40, as it affects FAR Part 27 Appendix C
The Amendments of 14 CFR Part 34 and Part 36 in effect on
the day the Type Certificate is issued
National Environmental Policy Act of 1969
Noise Control Act of 1972
[[Page 27448]]
Any Special conditions, Exemptions, and Equivalent Safety
Findings deemed necessary
In addition, the certification basis includes certain special
conditions and equivalent safety findings that are not relevant to this
special condition.
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.
In addition to the applicable airworthiness regulations and special
conditions, the Bell Model 427 helicopter must comply with the noise
certification requirements of 14 CFR part 36; and the FAA must issue a
finding of regulatory adequacy pursuant to Sec. 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. 21.17(a)(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, 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 Bell Model 427 helicopter will incorporate the following novel
or unusual design features: Electrical, electronic, or a combination of
electrical electronic (electrical/electronic) systems that perform
critical control functions, or provide critical displays. Examples of
such critical control functions and displays are electronic flight
instruments that will be providing displays critical to the continued
safe flight and landing of the helicopter during operation in
Instrument Meteorological Conditions (IMC), and Full Authority Digital
Engine Controls (FADEC) that will be performing engine control
functions that are critical to the continued safe flight and landing of
the helicopter during Visual Flight Rules (VFR) and Instrument Flight
Rules (IFR) operations.
Discussion
The Bell Model 427 helicopter, at the time of application, was
identified as incorporating one and possibly more electrical/electronic
systems, such as electronic flight instruments and FADEC. After the
design is finalized, Bell will provide the FAA with a preliminary
hazard analysis that will identify any other critical functions that
are performed by the electrical/electronic systems, and are required
for safe flight and landing.
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 incidents 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
[[Page 27449]]
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 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 non-critical
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
------------------------------------------------------------------------
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
------------------------------------------------------------------------
Table 2.--IFR Rotorcraft Field Strength Volts/Meter
------------------------------------------------------------------------
Frequency Peak Average
------------------------------------------------------------------------
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
------------------------------------------------------------------------
Applicability
As previously discussed, this special condition is applicable to
Bell Model 427 helicopters. Should Bell 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 helicopters. 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 Part 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 Bell Helicopter Textron Canada Model 427
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.
[[Page 27450]]
Issued in Fort Worth, Texas, on May 11, 1999.
Eric Bries,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 99-12743 Filed 5-19-99; 8:45 am]
BILLING CODE 4910-13-U
