[Federal Register Volume 70, Number 197 (Thursday, October 13, 2005)]
[Rules and Regulations]
[Pages 59630-59631]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-20459]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM331; Special Conditions No. 25-302-SC]


Special Conditions: Learjet Model 35 Series; 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 Learjet Model 35 
series airplanes modified by Avcon Industries Inc. These modified 
airplanes will have a novel or unusual design feature when compared to 
the state of technology envisioned in the airworthiness standards for 
transport category airplanes. The modification incorporates the 
installation of new Kollsman 24771 Air data computers and Thommen AD30 
displays. 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.

DATES: The effective date of these special conditions is October 4, 
2005. Comments must be received on or before November 14, 2005.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate to: Federal Aviation Administration, Transport Airplane 
Directorate, Attention: Rules Docket (ANM-113), Docket No. NM331 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. NM331.

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-
1320.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA has determined that notice and opportunity for prior public 
comment is impracticable because these procedures would significantly 
delay certification of the airplane and thus delivery of the affected 
aircraft. In addition, the substance of these special conditions has 
been subject to the public comment process in several prior instances 
with no substantive comments received. The FAA therefore finds that 
good cause exists for making these special conditions effective upon 
issuance; however, we invite interested persons to participate in this 
rulemaking by submitting written 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 based on the comments we receive.
    If you want the FAA to acknowledge receipt of your comments on 
these special conditions, 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 August 5, 2005, Avcon Industries, Inc., P.O. Box 748, Newton, 
Kansas, 67114, applied for a supplemental type certificate (STC) to 
modify Learjet Model 35 series airplanes currently approved under Type 
Certificate No. A10CE. The Learjet Model 35 airplanes are small 
transport category airplanes powered by two turbojet engines, with 
maximum takeoff weight of up to 18,000 lbs. These airplanes operate 
with 2-person crew and can seat up to 8 passengers. The proposed 
modification incorporates the installation of Kollsman 24771 Air Data 
Computers and Thommen AD30 displays. The avionics/electronics and 
electrical systems installed in this airplane are flight critical and 
have the potential to be vulnerable to high-intensity radiated fields 
(HIRF) external to the airplane.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Avcon Industries, Inc., must 
show that the Learjet Model 35 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 Learjet Model 35 series airplanes includes 14 CFR part 25 
effective February 1, 1965, as amended by Amendments 25-1, 25-2, 25-4, 
25-7, 25-18, and Sec.  25.571(d) of Amendment 25-10, Special Conditions 
set forth in FAA letter to Learjet dated March 1, 1967, and Special 
Conditions No. 25-50-CE-6 dated April 18, 1973, and Amendment 1 dated 
September 18, 1973. The certification basis for Models 35A also 
includes Special Conditions No. 25-72-CE-8 dated November 3, 1976, and 
Amendment 1 dated March 14, 1978. The certification basis for Model 35A 
(C-21A), in addition to the basis listed above, includes Special 
Conditions 25-ANM-28 dated May 3, 1989. In addition, the certification 
basis includes certain later amended sections of the applicable part 25 
regulations that are not relevant to these special conditions.
    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 series airplanes 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Learjet Model 35 series airplanes must comply with the 
fuel vent and exhaust emission requirements of 14 CFR part 34 and the 
noise certification requirements of 14 CFR 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.
    Special conditions are initially applicable to the model for which 
they are issued. Should Avcon Industries Inc., apply at a later date 
for a supplemental type certificate to modify any other model included 
on Type Certificate No. A10CE to incorporate the

[[Page 59631]]

same or similar novel or unusual design feature, these special 
conditions would also apply to the other model under the provisions of 
Sec.  21.101.

Novel or Unusual Design Features

    As noted earlier, the Learjet Model 35 series airplanes, as 
modified by Avcon Industries, Inc., will incorporate Kollsman 24771 Air 
data computers and Thommen AD30 displays. The Thommen displays and air 
data sensor perform critical functions. These systems may be vulnerable 
to high intensity radiated fields external to the airplane. The current 
airworthiness standards of part 25 do not contain adequate or 
appropriate safety standards for the protection of this equipment from 
the adverse effects of HIRF. Accordingly, this system is 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 35 series airplanes as 
modified by Avcon Industries, Inc. These special conditions require 
that new avionics/electronics and electrical systems 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, and the advent of space and satellite communications, 
coupled with electronic command and control of the airplane, the 
immunity of critical 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 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 
identified in the table below for the frequency ranges indicated. Both 
peak and average field strength components from the table are to be 
demonstrated.

------------------------------------------------------------------------
                                                       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
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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 35 series airplanes modified by Avcon Industries, Inc. 
Should Avcon Industries, Inc., apply at a later date for a supplemental 
type certificate to modify any other model included on Type Certificate 
No. A10CE to incorporate the same or similar novel or unusual design 
feature, these special conditions would apply to that model as well 
under the provisions of Sec.  21.101.

Conclusion

    This action affects only certain novel or unusual design features 
on Learjet Model 35 series airplanes modified by Avcon Industries, 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 these special conditions has been subjected to the 
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 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

0
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 35 series 
airplanes modified by Avcon Industries, Inc.
    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.
    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 October 4, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-20459 Filed 10-12-05; 8:45 am]
BILLING CODE 4910-13-P