[Federal Register Volume 63, Number 135 (Wednesday, July 15, 1998)]
[Rules and Regulations]
[Pages 38075-38077]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-18857]



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  Federal Register / Vol. 63, No. 135 / Wednesday, July 15, 1998 / 
Rules and Regulations  

[[Page 38075]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM147; Special Conditions No. 25-139-SC]


Special Conditions: Boeing Model 757-300; High-Intensity Radiated 
Fields

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Boeing Model 757-
300 airplane. This airplane will utilize new avionics/electronic 
systems that provide critical data to the flightcrew. The applicable 
regulations do not contain adequate or appropriate safety standards for 
the protection of these systems 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.

EFFECTIVE DATE: August 14, 1998.

FOR FURTHER INFORMATION CONTACT: John Dimtroff, FAA, Airplane and 
Flight Crew Interface Branch, ANM-111, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, 
Washington, 98055-4056, telephone (425) 227-2117 or facsimile (425) 
227-1320.

SUPPLEMENTARY INFORMATION:

Background

    On February 21, 1996, the Boeing Commercial Airplane Group, P. O. 
Box 3707, Seattle, Washington 98124-2207, applied for an amendment to 
Type Certificate No. A2NM to include the new Model 757-300, a 
derivative of the 757-200. The 757-300 is a swept-wing, conventional-
tail, twin-engine, turbofan-powered transport. Each engine is capable 
of delivering 43,100 pounds of thrust. The flight controls are 
unchanged beyond those changes deemed necessary to accommodate the 
stretched configuration. The airplane has a seating capacity of up to 
295, and a maximum takeoff weight of 270,000 pounds (122,470 Kg).

Type Certification Basis

    Under the provisions of Title 14 CFR 21.101, Boeing must show that 
the Model 757-300 meets the applicable provisions of the regulations 
incorporated by reference in Type Certificate No. A2NM, or the 
applicable regulations in effect on the date of application for the 
change to the Model 757-300. The regulations incorporated by reference 
in the type certificate are commonly referred to as the ``original type 
certification basis.'' The regulations incorporated by reference in 
Type Certificate No. A2NM include 14 CFR part 25, as amended by 
Amendments 25-1 through 25-45, and certain other later amended sections 
of part 25 that are not relevant to these special conditions. Except 
for certain earlier amended sections of part 25 that are not relevant 
to these special conditions, Boeing has chosen to comply with part 25 
as amended by Amendments 25-1 through 25-85, the applicable regulations 
in effect on the date of application. In addition to the applicable 
airworthiness regulations and special conditions, the 757-300 must 
comply with the fuel vent and exhaust emission requirements of part 34, 
effective September 10, 1990, plus any amendments in effect at the time 
of certification; and the noise certification requirements of part 36, 
effective December 1, 1969, as amended by Amendment 36-1 through the 
amendment in effect at the time of certification. These special 
conditions form an additional part of the type certification basis.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the 757-300 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 of the FAR after public notice, as required by Secs. 11.28 
and 11.29(b), and become part of the 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 Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The 757-300 airplane avionics enhancement utilizes electronic 
systems that perform critical functions, including the following 
airframe Line Replaceable Units (LRU): Multi-Mode Receiver (MMR), 
Flight Control Computer (FCC), Yaw Damper Stabilizer Trim Module (YSM), 
Air Data Inertial Reference System (ADIRS), and the Allied Signal Radio 
Altimeter (RA). These systems may be vulnerable to high-intensity 
radiated fields (HIRF) external to the airplane.

Discussion

    There is no specific regulation that addresses protection 
requirements for electrical and electronic systems from HIRF. 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, special 
conditions are needed for the 757-300, which require that new 
technology electrical and electronic systems, such as the MMR, FCC, 
YSM, ADIRS, and RA, be designed and installed to preclude component 
damage and interruption of function due to both the direct and indirect 
effects of HIRF.

High-Intensity Radiated Fields

    With the trend toward increased power levels from ground based 
transmitters, plus the advent of space and satellite communications, 
coupled with electronic command and control of

[[Page 38076]]

the airplane, the immunity of critical digital avionics systems to HIRF 
must be established.
    It is not possible to precisely define the HIRF to which the 
airplane will be exposed in service. There is also uncertainty 
concerning the effectiveness of airframe shielding for HIRF. 
Furthermore, coupling of electromagnetic energy to cockpit-installed 
equipment through the cockpit window apertures is undefined. Based on 
surveys and analysis of existing HIRF emitters, an adequate level of 
protection exists when compliance with the HIRF protection special 
condition is shown with either paragraphs 1 or 2 below:
    1. A minimum threat of 100 volts per meter peak electric field 
strength from 10 KHz to 18 GHz.
    a. The threat must be applied to the system elements and their 
associated wiring harnesses without the benefit of airframe shielding.
    b. Demonstration of this level of protection is established through 
system tests and analysis.
    2. A threat external to the airframe of the following field 
strengths for the frequency ranges indicated.

----------------------------------------------------------------------------------------------------------------
                                                          Field strength (volts per meter)                      
                                   -----------------------------------------------------------------------------
             Frequency                         US                    UK/European              Consolidated      
                                   -----------------------------------------------------------------------------
                                        Peak         Avg.         Peak         Avg.         Peak         Avg.   
----------------------------------------------------------------------------------------------------------------
10 kHz-100 kHz....................           30           30           50           50           50           50
100 kHz-500 kHz...................           40           30           60           60           60           60
500 kHz-2 MHz.....................           30           30           70           70           70           70
2 MHz-30 MHz......................          190          190          200          200          200          200
30 MHz-70 MHz.....................           20           20           30           30           30           30
70 MHz-100 MHz....................           20           20           30           30           30           30
100 MHz-200 MHz...................           30           30          150           30          150           30
200 MHz-400 MHz...................           30           30           70           70           70           70
400 MHz-700 MHz...................           80           80          700           40          700           80
700 MHz-1 GHz.....................          690          240         1700           80         1700          240
1 GHz-2 GHz.......................          970           70         5000          360         5000          360
2 GHz-4 GHz.......................         1570          350         4500          360         4500          360
4 GHz-6 GHz.......................         7200          300         5200          300         7200          300
6 GHz-8 GHz.......................          130           80         2000          330         2000          330
8 GHz-12 GHz......................         2100           80         3500          270         3500          270
12 GHz-18 GHz.....................          500          330         3500          180         3500          330
18 GHz-40 GHz.....................          780           20           NA           NA          780           20
  The field strengths are expressed in terms of peak root-mean-square (rms) values.                             
----------------------------------------------------------------------------------------------------------------

    The threat levels identified above differ from those used in 
previous special conditions and are the result of an FAA review of 
existing studies on the subject of HIRF, in light of the ongoing work 
of the Electromagnetic Effects Harmonization Working Group of the 
Aviation Rulemaking Advisory Committee. In general, these standards are 
less critical than the threat level that was previously used as the 
basis for earlier special conditions

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-98-02-SC for the 757-
300 was published in the Federal Register on March 25, 1998 (63 FR 
14381). Three commenters responded.
    The first commenter, representing the interests of airline pilots, 
concurs with the special conditions as proposed.
    The second commenter, the United Kingdom Civil Aviation Authority 
(CAA), states that harmonized HIRF requirements and associated guidance 
material arising from FAA/Joint Aviation Authorities (JAA) 
participation in a working group of the Aviation Rulemaking Advisory 
Committee (ARAC) are well established and known to the FAA and should 
be applied by the FAA where special conditions of this nature are 
required. The commenter also states that the JAA has applied the 
harmonized requirements and means of compliance, and as the FAA may be 
faced with finding compliance on behalf of the JAA, it may be 
inappropriate for the FAA to apply any special condition or means of 
compliance that is not in accordance with the harmonized standards.
    The FAA concurs with this commenter; however, at the time of 
application for certification of the 757-300, the requirements depicted 
in the certification program were not fully harmonized. The HIRF 
requirements in place at the time were as depicted in the proposed 
special condition. Future airplane certification programs will include 
the fully harmonized requirements. Also, Boeing can elect to use the 
newer, harmonized requirement table if they so choose.
    The applicant, Boeing Commercial Airplane Group, also provided 
comments on the proposed special conditions. Boeing does not believe a 
HIRF special condition should be applied to existing production 
airplane models. The FAA does not agree. Section 21.101 of 14 CFR part 
21 states that special conditions can be applied to both new and 
substantially complete redesigns of a component, equipment 
installation, or system installation. Upgrades of existing production 
airplanes, if the upgrade incorporates new or substantially complete 
redesigns of a component, equipment installation, or system 
installation, do fall within the scope of Sec. 21.101.
    Boeing also states that applying the HIRF special conditions would 
deter them from upgrading existing airplane models. The FAA has 
consistently applied the requirements in the HIRF special condition to 
avionics upgrades of existing production model airplanes. Many of these 
upgrades have been in the form of supplemental type certifications on 
Boeing airplanes and were designed and installed by applicants other 
than Boeing. The special conditions have not deterred other applicants 
from upgrading existing Boeing airplanes. Also, Boeing already applies 
the requirements within the HIRF special conditions to existing 
production model airplanes. When Boeing certified the Model 777-200 and 
the Model 777-300, components, equipment installations, or system 
installations from the Model 777-200, which were new or substantially 
redesigned, were shown to comply with the requirements of the HIRF 
special condition. When the engines on the Model 767 were upgraded to 
include Full Authority Digital Engine Controls

[[Page 38077]]

(FADECs), the FADECs were shown to comply with the HIRF special 
conditions. The FAA HIRF requirements have been consistent, and Boeing 
has been aware of and complied with these requirements for several 
years.
    Boeing further states that the HIRF special condition would 
effectively deter them from upgrading electronic equipment that 
incorporates safety and reliability enhancing features. The FAA 
requirements in the HIRF special condition reflect the need to address 
a known environmental hazard, recognized by the technical and 
regulatory community worldwide. Protection against this known 
environmental hazard is required by FAA for all systems performing 
functions whose failure would contribute to or cause a catastrophic 
failure condition that would prevent the continued safe flight and 
landing of the airplane. This policy applies, regardless of whether the 
new or significantly changed component, equipment, or system is 
intended to improve an unrelated safety or reliability issue. Improving 
one aspect of safety or reliability should not degrade another aspect 
of safety.
    The FAA has consistently applied the requirements in the HIRF 
special conditions to certification programs for over 12 years, 
regardless of whether the certification was based on a new airplane 
type, or a change to an existing airplane. Changing this policy for one 
model of Boeing airplanes would not be consistent with the FAA policy 
over the last 12 years. Therefore, special conditions for the 757-300 
are adopted as proposed in Notice 25-98-02-SC.

Applicability

    As discussed above, these special conditions are applicable 
initially to the Model 757-300 airplane. Should Boeing 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 certain design features only on the Model 757-
300. It is not a rule of general applicability and affects only the 
manufacturer who applied to the FAA for approval of these features on 
this model.

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 type certification basis for Boeing Model 757-300 series airplanes.
    1. Protection 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 
operation and operational capability of these systems to perform 
critical functions are not adversely affected when the airplane is 
exposed to high-intensity radiated fields.
    2. For the purpose of this special condition, 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 7, 1998.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-18857 Filed 7-14-98; 8:45 am]
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