[Federal Register Volume 64, Number 139 (Wednesday, July 21, 1999)]
[Rules and Regulations]
[Pages 38999-39001]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-18566]



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  Federal Register / Vol. 64, No. 139 / Wednesday, July 21, 1999 / 
Rules and Regulations  

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM159; Special Conditions No. 25-145-SC]


Special Conditions: Boeing Model 707-353B (USAF C-137) Airplanes; 
High Intensity Radiated Fields (HIRF) Protection

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for Boeing Model 707-353B 
(USAF C-137) airplanes. These airplanes will have novel and unusual 
design features when compared to the state of technology envisioned in 
the airworthiness standards for transport category airplanes. These 
design features include the installation of an inertial navigation 
system (INS) for which the current applicable airworthiness regulations 
do not contain adequate or appropriate safety standards with regard to 
protection of the system from the effects of high-intensity radiated 
fields. These special conditions contain the additional safety 
standards that the Administrator considers necessary to establish a 
level of safety equivalent to that established by the existing 
airworthiness standards.

DATES: The effective date of these special conditions is July 13, 1999. 
Comments must be received on or before August 20, 1999.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate to: Federal Aviation Administration, Transport Airplane 
Directorate, Attention: Rules Docket (ANM-114), Docket No. NM159, 1601 
Lind Avenue SW., Renton, Washington 98055-4056; or delivered in 
duplicate to the Transport Airplane Directorate at the above address. 
All comments must be marked: Docket No. NM159. Comments may be 
inspected in the Rules Docket weekdays, except Federal holidays, 
between 7:30 a.m. and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT: Mark Quam, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone 
(425) 227-2799; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

FAA's Determination as to Need for Public Process

    The FAA has determined that notice and opportunity for prior public 
comment hereon are impracticable because those procedures would 
significantly delay issuance of the approval design and, thus, the 
delivery of the affected aircraft.
    In addition, the substance of these special conditions has been 
subject to the public comment process in several prior instances with 
no substantive comments received. Thus, the FAA has previously provided 
the public with a number of opportunities to comment on proposed 
special conditions that are substantively identical to those at issue; 
and the FAA is reasonably assured that all interested members of the 
public have had an opportunity to comment and that their comments have 
been fully considered. The FAA, therefore, finds that additional 
redundant notices are unnecessary, and good cause exists for making 
these special conditions effective upon issuance.

Comments Invited

    Although this action is in the form of final special conditions 
and, for the reasons stated above, is not preceded by notice and an 
opportunity for public comment, comments are invited on this rule. 
Interested persons are invited to submit such written data, views, or 
arguments as they may desire. Communications should identify the 
regulatory docket or notice 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 conditions 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 notice must include a self-
addressed, stamped postcard on which the following statement is made: 
``Comments to Docket NM159.'' The postcard will be date stamped and 
returned to the commenter.

Background

    On August 7, 1998, Boeing Commercial Airplane Group, P.O. Box 7730, 
Wichita, Kansas 67277, made application to the FAA for a Supplemental 
Type Certificate(STC) for the Boeing Model B-707-353B airplane [known 
as the U.S. Air Force (USAF) C-137]. The proposed configuration of this 
model will incorporate an upgrade of the inertial navigation system 
(INS) from the Litton LTN-72 model to the LTN-92 model.
    The INS provides attitude, heading, and navigation data to the 
flight crew. Display of attitude information is considered a critical 
function. Critical functions must be designed and installed to ensure 
that their operations are not adversely affected by high intensity 
radiated fields (HIRF). The existing airworthiness regulations do not 
contain adequate or appropriate safety standards for protection from 
the effects of HIRF external to the airplane; therefore, a special 
condition is proposed.

Supplemental Type Certification Basis

    Under the provisions of 14 CFR Sec. 21.101 (``Designation of 
applicable regulations''), Boeing must show that the Model 707-353B 
(USAF C-137) airplanes meet the applicable provisions of the 
regulations incorporated by reference in Type Certificate No. 4A26, or 
the applicable regulations in effect on the date of application for the 
change to the Model 707-353B. The regulations incorporated by reference 
in the type certificate are commonly referred to as the ``original type 
certification basis.'' The certification basis for the Model 707-353B 
airplanes includes Civil Air Regulations (CAR) 4b, as amended by 
Amendments 4b-1, 4b-2, and 4b-3; and

[[Page 39000]]

additional requirements identified in Type Certificate Data Sheet 4A26.

Purpose of Special Conditions

    If the Administrator finds that the applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
an airplane because of a novel or unusual design feature of that 
airplane, the FAA may then prescribe special conditions to establish a 
level of safety equivalent to that established in the regulations. 
Special conditions are authorized under the provisions of 14 CFR 21.16 
(``Special conditions'').
    Special conditions, as appropriate, are issued in accordance with 
14 CFR 11.49, as required by Sec. Sec. 11.28 and 11.29, and become part 
of the airplane's type certification basis in accordance with 
Sec. 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 14 CFR 21.101(a)(1).

Novel or Unusual Design Features

    The Boeing STC for the Model 707-353B (USAF C-137) airplanes 
includes the upgrade of the INS system from the Litton LTN-72 model to 
the LTN-92 model. This INS contains electronic equipment for which the 
current airworthiness standards (14 CFR part 25) do not contain 
adequate or appropriate safety standards that address protecting this 
equipment from the adverse effects of HIRF. Accordingly, this system is 
considered to be a ``novel or unusual design feature.''

Discussion

    As stated previously, there is no specific regulation that 
addresses requirements for protection of electrical and electronic 
systems from HIRF external to the airplane. Increased power levels from 
ground-based radio transmitters and the growing use of sensitive 
electrical and electronic systems to command and control airplanes have 
made it necessary to provide adequate protection.
    To ensure that a level of safety is achieved equivalent to that 
intended by the regulations incorporated by reference, the FAA has 
determined that special conditions are needed for the Boeing Model 707-
353B (USAF C-137) modifed to include the upgraded INS. These special 
conditions will require that this system, which performs critical 
functions, must be designed and installed to preclude component damage 
and interruption of function due to both the direct and indirect 
effects of HIRF.

Protection of Systems from High-Intensity Radiated Fields (HIRF)

    Recent advances in technology have given rise to the application in 
aircraft designs of advanced electrical and electronic systems that 
perform functions required for continued safe flight and landing. Due 
to the use of sensitive solid-state advanced components in analog and 
digital electronics circuits, these advanced systems are readily 
responsive to the transient effects of induced electrical current and 
voltage caused by HIRF. Such HIRF can degrade electronic systems 
performance by damaging components or by upsetting system functions.
    Furthermore, the HIRF environment has undergone a transformation 
that was not foreseen when the current requirements were developed: 
Higher energy levels are radiated from transmitters that are used for 
radar, radio, and television. Also, the number of transmitters has 
increased significantly. There also is uncertainty concerning the 
effectiveness of airframe shielding for HIRF. Furthermore, coupling to 
cockpit-installed equipment through the cockpit window apertures is 
undefined.
    The combined effect of the technological advances in airplane 
design and the changing environment has resulted in an increased level 
of vulnerability of electrical and electronic systems required for the 
continued safe flight and landing of the airplane. Effective measures 
against the effects of exposure to HIRF must be provided during the 
design and installation of these systems.

Actions Required by Special Conditions

    The accepted maximum energy levels in which airplane system 
installations must be capable of operating safely are based on surveys 
and analyses of existing radio frequency emitters. These special 
conditions require that the airplane be evaluated under these energy 
levels for the protection of the electronic system and its associated 
wiring harness. These external threat levels, which are lower than 
previously required values, are believed to represent the worst case to 
which an airplane would be exposed in the operating environment.
    These special conditions require that the systems installed in 
aircraft that perform critical functions must be qualified to the HIRF 
environment defined in paragraph 1., below, or (as an option to a fixed 
value using laboratory tests) that defined in paragraph 2, below:
    1. The applicant may demonstrate that the operation and operational 
capability of the installed electrical and electronic systems that 
perform critical functions are not adversely affected when the airplane 
is exposed to the HIRF environment defined below:

------------------------------------------------------------------------
                                                 Field Strength  (volts
                                                       per meter)
                   Frequency                   -------------------------
                                                    Peak       Average
------------------------------------------------------------------------
10 kHz-100 kHz................................           50           50
100 kHz-500 kHz...............................           50           50
500 kHz-2 MHz.................................           50           50
2 MHz-30 MHz..................................          100          100
30 MHz-70 MHz.................................           50           50
70 MHz-100 MHz................................           50           50
100 MHz-200 MHz...............................          100          100
200 MHz-400 MHz...............................          100          100
400 MHz-700 MHz...............................          700           50
700 MHz-1 GHz.................................          700          100
1 GHz-2 GHz...................................         2000          200
2 GHz-4 GHz...................................         3000          200
4 GHz-6 GHz...................................         3000          200

[[Page 39001]]

 
6 GHz-8 GHz...................................         1000          200
8 GHz-12 GHz..................................         3000          300
12 GHz-18 GHz.................................         2000          200
18 GHz-40 GHz.................................          600         200
------------------------------------------------------------------------
The field strengths are expressed in terms of peak root-mean-square
  (rms) values.

        Or
    b. The applicant may demonstrate by a system laboratory test that 
the electrical and electronic systems that perform critical functions 
withstand an electromagnetic field strength of 100 volts per meter, 
without the benefit of airplane structural shielding, over a frequency 
range of 10 kHz to 18 GHz.

    Note: The field strength values for the HIRF environment and 
laboratory test levels are expressed in root-mean-square units 
measured during the peak of the modulation cycle, as many laboratory 
instruments indicate amplitude. These are commonly called ``peak-
rms'' values. The true peak field strength values will be higher by 
a factor of the square root of two.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 707-353B (USAF C-137) airplanes modified to include the 
upgraded INS. Should Boeing Commercial Airplane Group apply at a later 
date for a design change approval to the type certificate to include 
any other model incorporating the same novel or unusual design feature, 
these special conditions would apply to that model as well, under the 
provisions of 14 CFR 21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on the Boeing 707-353B (USAF C-137) airplanes. 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 airplane.
    Further, the substance of these special conditions 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 in this document. For 
this reason, and because a delay would significantly affect the 
certification of the airplane, which is imminent, the FAA has 
determined that prior public notice and comment are unnecessary and 
impracticable, and good cause exists for adopting these special 
conditions upon issuance. However, 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 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.
    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the supplemental type certification basis for the Boeing Model 707-353B 
(USAF C-137) airplanes.
    1. Protection of Electrical and Electronic Systems from Unwanted 
Effects of High-Intensity Radiated Fields (HIRF). Each electrical and 
electronic system that performs critical functions must be designed and 
installed to ensure that the operations and operational capability of 
these systems to perform critical functions are not adversely affected 
when the airplane is exposed to high-intensity radiated electromagnetic 
fields external to the airplane.
    2. For the purpose of these special conditions, the following 
definition applies:
    Critical Functions: Functions whose failure would contribute to or 
cause a failure condition that would prevent the continued safe flight 
and landing of the airplane.

    Issued in Renton, Washington, on July 13, 1999.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-18566 Filed 7-20-99; 8:45 am]
BILLING CODE 4910-13-U