[Federal Register Volume 59, Number 247 (Tuesday, December 27, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-31810]
[[Page Unknown]]
[Federal Register: December 27, 1994]
VOL. 59, NO. 247
Tuesday, December 27, 1994
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 29
[Docket No. 94-ASW-3; Notice No. SC-94-3-SW]
Special Condition: Bell Helicopter Textron Model 222U Helicopter,
Electronic Flight Instrument System
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed special condition.
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SUMMARY: This notice proposes a special condition for the Bell
Helicopter Textron, Inc., Model 222U helicopter modified by Heli-Dyne
Systems, Inc. This helicopter will have a novel or unusual design
feature associated with the Electronic Flight Instrument System. The
applicable airworthiness regulations do not contain adequate safety
standards for the protection of these critical function systems 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 airworthiness standards of part 29 of the Federal
Aviation Regulations.
DATES: Comments must be received on or before January 26, 1995.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration (FAA), Office of the Assistant Chief
Counsel, Attn: Rules Docket No. 94-ASW-3, 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. 94-ASW-3. 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, Policy and
Procedures Group, Fort Worth, Texas 76193-0112; 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. 94-ASW-3.'' The postcard will be date and time stamped and returned
to the commenter.
Background
On May 16, 1994, Heli-Dyne Systems, Inc., Hurst, Texas, applied for
a Supplemental Type Certificate for installation of an Electronic
Flight Instrument System in the Bell Helicopter Textron (BHTI) Model
222U helicopter. This model helicopter is a 10 passenger, 2 engine,
8,250 pound (Category B) or 7,850 pound (Category A) transport category
helicopter.
Type Certification Basis
The certification basis established for the BHTI Model 22U
helicopter includes: 14 CFR 21.29 and part 29 of the Federal Aviation
Regulations (FAR) effective February 1, 1965 (Transport Categories A
and B), Amendments 29-1 through 29-9; Amendment 29-11; Sec. 29.997 of
Amendment 29-10; Sec. 29.927(b)(2) of Amendment 29-17; Secs. 29.801,
29.25(c) 29.865, 29.1557(c), and 29.1555(c) of Amendment 29.12;
Secs. 29.1, 29.79, 29.1517, and 29.1587 of Amendment 29-21; Criteria
for Helicopter Instrument Flight Rule (IFR) certification dated
December 15, 1978; Exemption No. 2789, Sec. 29.811(h)(1) (following
Amendment 24, effective December 6, 1984, Sec. 29.811(h)(1) became
Sec. 29.811(f)(2)); and Exemption No. 4395, Sec. 29.855(a) and portions
of Sec. 29.855(d).
If the Administration 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
Sec. 11.49 of the FAR after public notice, 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).
Discussion
The BHTI Model 222U helicopter, at the time of the application for
modification by Heli-Dyne Systems, Inc., 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. The electronic flight instrument
system performs the attitude display function. The display of attitude,
altitude, and airspeed is critical to the continued safe flight and
landing of the helicopters for IFR operations in instrument
meteorological conditions. After the design is finalized, Heli-Dyne
Systems, Inc., will provide the FAA with a preliminary hazard that will
identify any other critical functions performed by the electrical/
electronic systems that are critical to the continued safe flight and
landing of the helicopters.
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 high intensity radiated
fields (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.
Furthermore, 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 of 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 to 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 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.
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 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 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.
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 KH2.......................................... 50 50
100-500............................................. 60 60
500-2,000........................................... 70 70
2-30 MH2............................................ 200 200
30-100.............................................. 30 30
100-200............................................. 150 33
200-400............................................. 70 70
400-700............................................. 4,020 935
700-1,000........................................... 1,700 170
1-2 GH2............................................. 5,000 990
2-4................................................. 6,680 840
4-6................................................. 6,850 310
6-8................................................. 3,600 670
8-12................................................ 3,500 1,270
12-18............................................... 3,500 360
18-40............................................... 2,100 750
------------------------------------------------------------------------
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 applicant 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: 49 U.S.C. 1344, 1348(c), 1352, 1354(a), 1355, 1421
through 1431, 1502, 1651(b)(2); 42 U.S.C. 1857f-10 4321 et seq.;
E.O. 11514; 49 U.S.C. 106(g).
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 Bell Helicopter Textron Model 222U 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 December 16, 1994.
Eric Bries,
Acting Manager, Rotorcraft Directorate Aircraft Certification Service.
[FR Doc. 94-31810 Filed 12-23-94; 8:45 am]
BILLING CODE 4910-13-M
