[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
------------------------------------------------------------------------
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