[Federal Register Volume 61, Number 90 (Wednesday, May 8, 1996)]
[Proposed Rules]
[Pages 20760-20762]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-11496]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 29
[Docket No. 96-ASW-2; Notice No. SC-96-2-SW]


Special Condition: Sikorsky Model S76C, High Intensity Radiated 
Fields

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed special condition.

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SUMMARY: This notice proposes a special condition for the Sikorsky 
Model S76C helicopter. This helicopter 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 for 
the protection of electronic systems that perform critical functions 
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 applicable airworthiness 
standards.

DATES: Comments must be received on or before June 7, 1996.

ADDRESSES: Comments on this proposal may be mailed in duplicate to the 
Federal Aviation Administration (FAA), Office of the Assistant Chief 
Counsel, Attn: Rules Docket No. 96-ASW-2, 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. 96-ASW-2. 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, Regulations Group, 
Fort Worth, Texas 76193-0110; 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. 96-ASW-2.'' The postcard will be date and time stamped and returned 
to the commenter.

Background

    Sikorsky Aircraft Corporation, Stratford, Connecticut, applied for 
an amendment to the Type Certificate for Model S76C helicopter on 
August 15, 1990. The amendment will allow installation of Turbomeca 
Arriel Model 2S1 engines with FADEC control and 30 second/2 minute 
ratings as alternate engines for the Sikorsky Model S76C helicopter. 
This is a 12 (14 including crew) passenger, twin engine, 11,700 pound 
transport category helicopter.

Type Certificate Basis

    The type certification basis is 14 Code of Federal Regulations part 
29, February 1, 1965, and Amendments 29-1 through 29-11; in addition, 
portions of Amendment 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); Amendment 29-13, specifically Sec. 29.965; Amendment 29-24, 
specifically Sec. 29.1325; Amendment 29-30 specifically Sec. 29.811; 
Amendment 29-34, specifically Secs. 29.67(a)(1)(i), 29.923(a), (b) (1) 
& (3), 29.1143(f), 29.1305(a) (24) & (25), 29.1521 (i) & (j) and 
29.1549(e); and Amendment 36-14 of 14 CFR part 36, Appendix H.
    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 to 
establish a level of safety equivalent to that established in the 
regulations.
    Special conditions, as appropriate, are issued in accordance with 
Federal Aviation Administration Sec. 11.49 after public notice, as 
required by Secs. 11.28 and 11.29(b), and become part of the type 
certification basis in accordance with Federal Aviation Administration 
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).

Discussion

    The Sikorsky Model S76C helicopter, at the time of the application 
for amendment to U.S. Type Certificate

[[Page 20761]]

H1NE, 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. A Full Authority 
Digital Engine Control (FADEC) is an example of an electronic device 
that performs the critical functions of engine control. The control of 
the engines is critical to the continued safe flight and landing of the 
helicopter during visual flight rules (VFR) and instrument flight rules 
(IFR) operations.
    If it is determined that this helicopter currently or at a future 
date incorporates other electrical/electronic systems performing 
critical functions, those systems also will be required to comply with 
the requirements of this special condition.
    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 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.
    Futhermore, 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 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 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

[[Page 20762]]

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 500 
MHZ and 1 KHZ square wave with greater than 90 percent depth 
of modulation from 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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    As discussed above, these special conditions are applicable 
initially to the Sikorsky Model S76C helicopter. Should Sikorsky 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 conditions would apply to that model as well, under the 
provisions of Sec. 21.101(a)(1).

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 manufacturer 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: 42 U.S.C. 7572; 49 U.S.C. 106(g), 40105, 40113, 
44701, 44702, 44704, 44709, 44711, 44713, 44715, 45303.

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 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 
helicopters are exposed to high intensity radiated fields external to 
the helicopters.

    Issued in Fort Worth, Texas, on April 26, 1996.
Larry M. Kelly,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 96-11496 Filed 5-7-96; 8:45 am]
BILLING CODE 4910-13-M