[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