[Federal Register Volume 68, Number 82 (Tuesday, April 29, 2003)]
[Rules and Regulations]
[Pages 22578-22580]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-10450]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM247, Special Conditions No. 25-232-SC]


Special Conditions: Learjet Model 24/25 Series 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 the Learjet Model 24/
25 series airplanes, as modified by LJSC Ltd. 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. The modification incorporates the installation of 
dual IS&S air data display units (ADDU) and a single IS&S analog 
interface unit (AIU). 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 provided by the existing 
airworthiness standards.

DATES: The effective date of these special conditions is April 14, 
2003. Comments must be received on or before May 29, 2003.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate to: Federal Aviation Administration, Transport Airplane 
Directorate, Attn: Rules Docket (ANM-113), Docket No.NM247, 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. NM247. Comments may be inspected in 
the Rules Docket weekdays, except Federal holidays, between 7:30 a.m. 
and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Greg Dunn, 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) 227-2799; facsimile (425) 227-
1149.

SUPPLEMENTARY INFORMATION:

FAA's Determination as to Need for Public Process

    The FAA has determined that notice and opportunity for prior public 
comment are unnecessary in accordance with 14 CFR 11.38, because the 
FAA has provided previous opportunities to comment on substantially 
identical special conditions and has fully considered and addressed all 
the substantive comments received. Based on a review of the comment 
history and the comment resolution, the FAA is satisfied that new 
comments are unlikely. The FAA, therefore, finds that good cause exists 
for making these special conditions effective upon issuance. However, 
the FAA invites interested persons to participate in this rulemaking by 
submitting comments, data, or views. The most helpful comments 
reference a specific portion of the special conditions, explain the 
reason for any recommended change, and include supporting data. We ask 
that you send us two copies of written comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning these special conditions. The docket is available for public 
inspection before and after the comment closing date. If you wish to 
review the docket in person, go to the address in the ADDRESSES section 
of this preamble between 7:30 a.m. and 4 p.m., Monday through Friday, 
except Federal holidays.
    We will consider all comments we receive on or before the closing 
date for comments. We will consider comments filed late if it is 
possible to do so without incurring expense or delay. We may change 
these special conditions in light of the comments we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it back to you.

Background

    On October 8, 2002, LJSC Ltd., 8201 E. 34th North Building 800, 
Suite 805, Wichita, Kansas 67226, applied for a supplemental type 
certificate (STC) to modify the Learjet Model 24/25 series airplanes 
approved under Type Certificate No. A10CE. The modification 
incorporates the installation of dual IS&S air data display units 
(ADDU), and a single IS&S analog interface unit (AIU).
    The dual IS&S air data display units (ADDU) and single IS&S analog

[[Page 22579]]

interface unit (AIU) replace the existing altimetry system. This system 
uses electronics to a far greater extent than the original altimetry 
system, and may be more susceptible to electrical and magnetic 
interference caused by high-intensity radiated fields (HIRF). 
Disruption of these signals could result in loss of altitude, or 
present misleading information to the pilot.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Amendment 21-69, effective 
September 16, 1991, LJSC Ltd. must show that the Learjet Model 24/25 
series 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 24/25 series airplanes includes 14 CFR part 25 
effective February 1, 1965, as amended by 25-2 and 25-4. Other 
applicable amendments, regulations, and special conditions are noted in 
Type Certificate Data Sheet (TCDS) A10CE.
    If the Administrator finds that the applicable airworthiness 
regulations (that is, 14 CFR part 25, as amended) do not contain 
adequate or appropriate safety standards for the Learjet Model 24/25 
series airplanes because of novel or unusual design features, special 
conditions are prescribed under the provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Learjet Model 24/25 series airplanes must comply with 
the fuel vent and exhaust emission requirement of 14 CFR part 34 and 
the noise certification requirement of part 36.
    Special conditions, as defined in 14 CFR 11.19, are issued in 
accordance with Sec.  11.38, 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 LJSC Ltd. apply at a later date for a 
supplemental type certificate to modify any other model already 
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 14 CFR 21.101(a)(1).

Novel or Unusual Design Features

    The Learjet Model 24/25 series airplanes will incorporate the 
installation of dual IS&S air data display units (ADDU) and a single 
IS&S analog interface unit (AIU). Because these advanced systems use 
electronics to a far greater extent than the original altimetry system, 
they may be more susceptible to electrical and magnetic interference 
caused by high-intensity radiated fields (HIRF) external to the 
airplane. 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. 
Accordingly, these instruments are considered to be a novel or unusual 
design feature.

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 avionics/electronics and electrical 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 24/25 series airplanes, as 
modified to include the new altimetry system. These special conditions 
will require that the new dual IS&S air data display units (ADDU) and 
single IS&S analog interface unit (AIU), which 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/electronics and electrical 
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 in accordance with either paragraph 1 OR 2 below:
    1. A minimum threat of 100 volts rms (root-mean-square) 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 field strengths 
indicated in the table below for the frequency ranges indicated. Both 
peak and average field strength components from the table below are to 
be demonstrated.

------------------------------------------------------------------------
                                                        Field strength
                                                       (volts per meter)
                      Frequency                      -------------------
                                                        Peak     Average
------------------------------------------------------------------------
10kHz-100kHz........................................        50        50
100kHz-500kHz.......................................        50        50
500kHz-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 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.

Applicability

    As discussed above, these special conditions are applicable to 
Learjet Model 24/25 series airplanes modified by LJSC Ltd. to include 
the dual IS&S air data display units (ADDU) and a single IS&S analog 
interface unit (AIU). Should LJSC Ltd. apply at a later date for a 
supplemental type certificate to modify any other model already 
included on Type Certificate A10CE to incorporate the same novel or 
unusual design features, these special conditions would apply to that 
model as well under the provisions of 14 CFR 21.101(a)(1).

[[Page 22580]]

Conclusion

    This action affects only certain design features on Learjet Model 
24/25 series airplanes modified by LJSC Ltd. 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 notice and comment procedure in several prior instances 
and has been derived without substantive change from those previously 
issued. 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.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and record keeping 
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 supplemental type certification basis for Learjet Model 24/25 
series airplanes modified by LJSC Ltd.
    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 external to the airplane.
    2. 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 April 14, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 03-10450 Filed 4-28-03; 8:45 am]
BILLING CODE 4910-13-P