Airworthiness standards: Special conditions— 82; high intensity radiated fields,

[Federal Register: June 23, 1998 (Volume 63, Number 120)]

[Rules and Regulations]

[Page 34121-34123]

From the Federal Register Online via GPO Access [wais.access.gpo.gov]

[DOCID:fr23jn98-2]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM149, Special Conditions No. 25-138-SC]

Special Conditions: McDonnell Douglas DC-9-81,-82 Airplanes; High Intensity Radiated Fields (HIRF)

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

SUMMARY: These special conditions are issued for McDonnell Douglas DC- 9-81, -82 airplanes modified by Midwest Express Airlines. 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 special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that provided by the existing airworthiness standards.

DATES: The effective date of these special conditions is June 11, 1998. Comments must be received on or before August 7, 1998.

ADDRESSES: Comments on these special conditions may be mailed in duplicate to: Federal Aviation Administration, Office of the Assistant Chief Counsel, Attn: Rules Docket (ANM-7), Docket No. NM149, 1601 Lind Avenue SW., Renton, Washington, 98055-4056; or delivered in duplicate to the Office of the Assistant Chief Counsel at the above address. Comments must be marked: Docket No. NM149. 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: Connie Beeane, 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) 227-2796.

SUPPLEMENTARY INFORMATION:

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 docket and special conditions 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 submitted 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 filedin the docket. Persons wishing the FAA to acknowledge receipt of their comments submitted in response to this request must submit with those comments a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket No. NM149.'' The postcard will be date stamped and returned to the commenter.

Background

On March 12, 1998, Midwest Express Airlines applied for a supplemental type certificate (STC) to modify McDonnell Douglas DC-9- 81, -82 airplanes listed on Type Certificate A6WE. The modification incorporates the installation of electronic flight instrument system (EFIS) for display of critical flight parameters (altitude, airspeed, and attitude) to the crew. These displays can be susceptible to disruption to both command/response signals as a result of electrical and magnetic interference. This disruption of signals could result in loss of all critical flight displays and annunciations or present misleading information to the pilot.

[[Page 34122]]

Type Certification Basis

Under the provisions of 14 CFR Sec. 21.101, Midwest Express Avionics must show that the McDonnell Douglas DC-9-81, -82 airplanes, as changed, continue to meet the applicable provisions of the regulations incorporated by reference in Type Certificate No. A6WE, 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 certification basis for the modified McDonnell Douglas DC-9-81, -82 airplanes include 14 CFR part 25, dated February 1, 1965, with Amendments 1 through 40, as amended by TCDS A6WE.

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 McDonnell Douglas DC-9-81, -82 airplanes because of novel or unusual design features, 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 14 CFR 11.49 after public notice, as required by Secs. 11.28 and 11.29, 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 Midwest Express Airlines apply at a later date for design change approval to modify any other model already included on the same type certificate to incorporate the same novel or unusual design feature, these special conditions would also apply to the other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

The modified McDonnell Douglas DC-9-81, -82 will incorporate a new electronic flight instrument system (EFIS), which was not available at the time of certification of these airplanes, that performs critical functions. This system may be vulnerable to 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 McDonnell Douglas DC-9-81, -82, which require that new electrical and electronic systems, such as the EFIS, that perform 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 paragraphs 1, OR 2 below:

  1. A minimum threat of 100 volts per meter peak electric field strength from 10 KHz to 18 GHz.

    1. The threat must be applied to the system elements and their associated wiring harnesses without the benefit of airframe shielding.

    2. 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

    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 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.

    The threat levels identified above differ from those used in previous special conditions 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.

    Applicability

    As discussed above, these special conditions are applicable to McDonnell Douglas DC-9-81, -82 airplanes modified by Midwest Express Airlines. Should Midwest Express Airlines apply at a later date for design change approval to modify any other model included on the same type certificate to incorporate the same novel or unusual design feature, these special conditions would apply to that model as well under the provisions of Sec. 21.101(a)(1).

    Conclusion

    This action affects only certain design features on McDonnell Douglas DC-9-81, -82 airplanes modified by Midwest Express Avionics. 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.

    The substance of the special conditions for this airplane has been subjected to the notice and comment procedure 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 immediately. Therefore, these special conditions are being made effective upon issuance. The FAA is requesting comments to allow interested persons to submit views that may not have been submitted in

    [[Page 34123]]

    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 type certification basis for McDonnell Douglas DC-9-81, -82 airplanes modified by Midwest Express Airlines.

  3. 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. 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 June 11, 1998. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

    [FR Doc. 98-16632Filed6-22-98; 8:45 am]

    BILLING CODE 4910-13-P