[Federal Register Volume 59, Number 83 (Monday, May 2, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-10288]
[[Page Unknown]]
[Federal Register: May 2, 1994]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 29
[Docket No. 94-ASW-1; Special Condition 29-ASW-13]
Special Condition: Sikorsky Model S76C Helicopter, Electronic
Flight Instrument System
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final special condition; request for comments.
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SUMMARY: This special condition is issued for the Sikorsky Model S76C
helicopter modified by Sikorsky Aircraft, a Division of United
Technologies Corporation. 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 or
appropriate safety standards for the protection of these critical
function systems from the effects of external high intensity radiated
fields (HIRF). This special condition contains additional safety
standards that the Administrator considers necessary to establish a
level of safety equivalent to that provided by the applicable
airworthiness standards.
DATES: The effective date of this special condition is May 2, 1994.
Comments must be received on or before June 1, 1994.
ADDRESSES: Comments may be mailed in duplicate to: Federal Aviation
Administration (FAA), Office of the Assistant Chief Counsel, Attn:
Rules Docket No. 94-ASW-1, Fort Worth, Texas 76193-0007, or delivered
in duplicate to the Office of the Assistant Chief Counsel, 2601 Meacham
Blvd., room 663, Fort Worth, Texas 76137.
Comments must be marked Docket No. 94-ASW-1. 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: 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 delay delivery of the affected helicopter. These notice
and comment procedures are also considered unnecessary since the public
has been previously provided with a substantial number of opportunities
to comment on substantially identical special conditions and their
comments have been fully considered. Therefore, good cause exists for
making this special condition effective upon issuance.
Comments Invited
Although this final special condition was not subject to notice and
opportunity for prior public comment, comments are invited on this
final special condition. Interested persons are invited to comment on
this final 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 under the caption ADDRESSES. All communications received on
or before the closing date for comments will be considered. This
special condition 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-1.'' The postcard will be date
and time stamped and returned to the commenter.
Background
On October 12, 1993, Sikorsky Aircraft, West Palm Beach, Florida,
applied for a Supplemental Type Certificate for installation of an
Electronic Flight Instrument System in a Sikorsky Aircraft Model S76C
helicopter. This is a 13 passenger, twin engine, 11,400 pound transport
category helicopter.
Type Certification Basis
The certification basis established for the Sikorsky Model S76C
helicopter includes: 14 CFR part 29 (part 29) effective February 1,
1965, Amendments 29-1 through 29-11; in addition, portions of
Amendments 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);
portions of Amendment 29-13, specifically Sec. 29.965; Sec. 29.1325 of
Amendment 29-24; Sec. 29.811 of Amendment 29-30; Amendment 36-14 of
part 36, appendix H; instrument flight criteria for S-76 (interim)
dated February 10, 1977; Special Conditions 29-82-NE-3 (Docket No.
17721) dated March 27, 1978; Equivalent Safety Finding for
Sec. 29.173(b), National Environmental Act of 1969; Noise Control Act
of 1972; Sec. 29.865 including Sec. 29.25 of Amendment 29-12, when
cargo hook system, P/N 76255-02000, is installed; and for external load
operations, part 133, including Amendments 1-4. Compliance with the
following optional requirements has been established: Ditching
provisions Sec. 29.563 including Secs. 29.801 and 29.807(d) and
excluding Secs. 29.1411, 29.1415, and 29.1561 of Amendment 29-12, when
emergency flotation gear, P/N 76076-02002, is installed. For over-water
operations, compliance with the operating rules and Secs. 29.1411,
29.1415, and 29.1561 must be shown.
If the Administrator finds that the applicable airworthiness
regulations do not contain adequate or appropriate safety standards for
this helicopter 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 and become part of the type certification basis in
accordance with Sec. 21.101(b)(2). Provision is made for the public
comment period in Sec. 11.28.
Discussion
The Sikorsky Model S76C helicopter, at the time of the application
for modification by Sikorsky Aircraft, was identified as having
modifications that incorporate 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,
Sikorsky Aircraft will provide the FAA with a preliminary hazard
analysis 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 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 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 special condition is based
on many critical assumptions. With the exception of takeoff and landing
at an airport, one of these assumptions is that 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
capabilities 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 shown, by past testing, 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 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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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 helicopter.
The substance of this special condition for similar installations
in a variety of helicopters has been subjected to the notice and
comment procedure and has finalized without substantive change. 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 impractical, and good cause exists for
adopting this special condition immediately. Therefore, this special
condition is being made effective upon issuance. The FAA is requesting
comments to allow interested persons to submit views that may not have
been submitted in response to prior opportunities for comment.
List of Subjects in 14 CFR Part 29
Aircraft, Air transportation, Aviation safety, Rotorcraft, Safety.
The authority citations for this special condition are 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 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 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 helicopter
is exposed to high intensity radiated fields external to the
helicopter.
Issued in Fort Worth, Texas, on April 14, 1994.
Mark R. Schilling,
Acting Manager, Rotorcraft Directorate Aircraft Certification Service.
[FR Doc. 94-10288 Filed 4-29-94; 8:45 am]
BILLING CODE 4910-13-M
