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Special Conditions: Boeing Model 747-2G4B Series Airplanes; High-Intensity Radiated Fields (HIRF)

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Federal Aviation Administration (FAA), DOT.


Final special conditions; request for comments.


These special conditions are issued for Boeing Model 747-2G4B series airplanes modified by Boeing Airplane Services. These modified airplanes will have novel or unusual design features when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. The modification incorporates the installation of new Electronic Flight Instrument System (EFIS) displays. The EFIS displays will utilize electrical and electronic systems that perform critical functions. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for the protection of these systems from the effects of high-intensity-radiated fields (HIRF). 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.


The effective date of these special conditions is July 27, 2000.

Comments must be received on or before September 5, 2000.


Comments on these special conditions may be mailed in duplicate to: Federal Aviation Administration, Transport Airplane Directorate, Attention: Rules Docket (ANM-114), Docket No. NM173, 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. NM173. Comments may be inspected in the Rules Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

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Mark Quam, FAA, Standardization Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone (425) 227-2145; facsimile (425) 227-1149.

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Comments Invited

The FAA has determined that good cause exists for making these special conditions effective upon issuance; however, 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. These 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 No. NM173.” The postcard will be date stamped and returned to the commenter.


On August 25, 1997, Boeing Airplane Services, Wichita Division, P.O. Box 7730, Wichita, KS 67277-7730, applied for a Supplemental Type Certificate (STC) for the Boeing Model 747-2G4B series airplanes. The Boeing Model 747-2G4B is a Model 747-200 series airplane with four CF6-80C2B1 engines. The Model 747-200 series airplanes are an extended range passenger version of the Model 747-100 airplanes with changes to increase its strength and fuel capacity. The Model 747-2G4B will incorporate an Electronic Flight Instrument System (EFIS), which displays attitude and heading information and is manufactured by Astronautics. The modified airplanes are scheduled for certification in November 2000.

The Astronautics EFIS is a critical function that displays attitude and heading information. The EFIS must be designed and installed to ensure that their operations are not adversely affected by high intensity radiated fields (HIRF). These functions can be susceptible to disruption of both command and response signals as a result of electrical and magnetic interference caused by HIRF external to the airplane. This disruption of signals could result in loss of critical flight displays and annunciations, or could present misleading information to the pilot.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Boeing Airplane Services must show that the Boeing Model 747-2G4B series airplanes, as changed, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A20WE or the applicable regulations in effect on the date of application for the change. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations included in the certification basis for the Boeing Model 747-2G4B series airplanes include Title 14, Code of Federal Regulations (14 CFR) part 25, as amended by Amendments 25-1 through 25-8, plus additional requirements in Type Certificate Data Sheet (TCDS) A20WE. Start Printed Page 47842

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 Boeing Model 747-2G4B series airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Boeing Model 747-2G4B series airplanes must comply with the fuel vent and exhaust emission requirement of 14 CFR part 34 and the noise certification requirement of 14 CFR part 36.

Special conditions, as appropriate, are issued in accordance with § 11.49, as required by §§ 11.28 and 11.29, and become part of the airplane's type certification basis in accordance with § 21.101(b)(2).

Special conditions are initially applicable to the model for which they are issued. Should the applicant apply for a supplemental type certificate to modify any other model included on the same type certificate to incorporate the same novel or unusual design features, these special conditions would also apply to the other model under the provisions of § 21.101(a)(1).

Novel or Unusual Design Features

The Boeing Model 747-2G4B series airplanes will incorporate the Astronautics EFIS system, which performs critical functions. The EFIS system 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. This system may be vulnerable to HIRF external to the airplane. Accordingly, this system is considered to be a novel or unusual design feature.


There is no specific regulation that addresses the requirements for protection of 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 that is equivalent to that intended by the regulations incorporated by reference, special conditions are needed for the Boeing Model 747-2G4B airplanes modified to include the Astronautics EFIS system. These special conditions will require that this system, which performs critical functions, 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 (HIRF)

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 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 paragraph 1 OR 2 below:

1. A minimum threat of 100 volts rms per meter 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. Both peak and average field strength components from the Table are to be demonstrated.

FrequencyField strength (volts per meter)
10 kHz-100 kHz5050
100 kHz-500 kHz5050
500 kHz-2 MHz5050
2 MHz-30 MHz100100
30 MHz-70 MHz5050
70 MHz-100 MHz5050
100 MHz-200 MHz100100
200 MHz-400 MHz100100
400 MHz-700 MHz70050
700 MHz-1 GHz700100
1 GHz-2 GHz2000200
2 GHz-4 GHz3000200
4 GHz-6 GHz3000200
6 GHz-8 GHz1000200
8 GHz-12 GHz3000300
12 GHz-18 GHz2000200
18 GHz-40 GHz600200
The field strengths are expressed in terms of peak of the root-mean-square (rms) over the complete modulation period.

The threat levels identified above 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.


As discussed above, these special conditions are applicable to the Boeing Model 747-2G4B series airplanes modified by Boeing to include the Astronautics EFIS system. Should Boeing Airplane Services apply at a later date for a supplemental type certificate to modify any other model included on Type Certificate A20WE to incorporate the same novel or unusual design features, these special conditions would apply to that model as well under the provisions of § 21.101(a)(1).


This action affects only certain novel or unusual design features on the Boeing Model 747-2G4B series airplanes modified by Boeing Airplane Services. 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 airplanes.

The substance of the 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 herein. 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. 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.

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List of Subjects in 14 CFR Part 25

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The authority citation for these special conditions is as follows:

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

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The Special Conditions

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Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the

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2. For the purpose of these special conditions, the following definition applies:

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Issued in Renton, Washington, on July 27, 2000

Vi L. Lipski,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 00-19841 Filed 8-3-00; 8:45 am]