[Federal Register Volume 64, Number 59 (Monday, March 29, 1999)]
[Rules and Regulations]
[Pages 14818-14820]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-7626]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR part 25
[Docket No. NM153, Special Conditions No. 25-143-SC]
Special Conditions: Learjet Model 35, 35A, 36, 36A Airplanes;
High Intensity Radiated Fields (HIRF)
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final special conditions; request for comments.
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SUMMARY: These special conditions are issued for Learjet Model 35, 35A,
36, 36A airplanes modified by Learjet, Inc. 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 March 19,
1999; Comments must be received on or before April 28, 1999.
ADDRESSES: Comments on these special conditions may be mailed in
duplicate to: Federal Aviation Administration, Office of the Regional
Counsel, Attn: Rules Docket (ANM-7), Docket No. NM153, 1601 Lind Avenue
SW., Renton, Washington, 98055-4056; or delivered in duplicate to the
Office of the Regional Counsel at the above address. Comments must be
marked: Docket No. NM153. 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: Ross Landes, FAA, Standardization
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification
Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056;
telephone (425) 227-1071; facsimile (425) 227-1149.
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 regulatory docket and
special conditions
[[Page 14819]]
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. NM153.'' The postcard will be date stamped and returned
to the commenter.
Background
On January 7, 1999, Learjet, Inc. applied for a supplemental type
certificate (STC) to modify Learjet Model 35, 35A, 36, and 36A
airplanes listed on Type Certificate A10CE. The modification
incorporates the installation of dual LITEF LCR-92, Attitude and
Heading Reference Systems (AHRS) that provide air data input to both
pilot and copilot flight instruments displaying critical flight
parameters (attitude) to the flightcrew. The AHRS 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.
Type Certification Basis
Under the provisions of 14 CFR 21.101, Learjet, Inc. must show that
the Learjet Model 35, 35A, 36, and 36A airplanes, as changed, continue
to meet the applicable provisions of the regulations incorporated by
reference in Type Certificate No. A10CE, 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 Learjet Model 35, 35A, 36, and 36A airplanes
includes 14 CFR part 25, dated February 1, 1965, with Amendments 25-1
through 25-18, as amended by Type Certificate Data Sheet (TCDS) A10CE.
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 Learjet Model 35, 35A, 36, and 36A
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
Sec. 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 Learjet, Inc. apply at a later date for a
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 Learjet Model 35, 35A, 36, and 36A airplanes will
incorporate a new dual Attitude and Heading Reference System (AHRS)
that performs critical functions and was not available at the time of
certification of these airplanes. This system 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 Learjet Model 35, 35A, 36, and 36A which
require that new electrical and electronic systems, such as the AHRS,
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.
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Frequency
Field strength (volts per meter) -------------------------------
Peak Average
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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
[[Page 14820]]
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
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The field strengths are expressed in terms of peak root-mean-square
(rms) values.
The threat levels identified above differ from those used in
earlier special conditions. They 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
Learjet Model 35, 35A, 36, and 36A airplanes modified by Learjet, Inc.
Learjet Inc. may 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 Learjet Model
35, 35A, 36, and 36A airplanes modified by Learjet, Inc. 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
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 Learjet Model 35, 35A, 36, and 36A
airplanes modified by Learjet, Inc.
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 March 19, 1999.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 99-7626 Filed 3-26-99; 8:45 am]
BILLING CODE 4910-13-P
