[Federal Register Volume 63, Number 120 (Tuesday, June 23, 1998)]
[Rules and Regulations]
[Pages 34121-34123]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-16632]


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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.

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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 filed in 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.
    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                    -----------------------
                                                     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.
    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. 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. 98-16632 Filed 6-22-98; 8:45 am]
BILLING CODE 4910-13-P