[Federal Register Volume 68, Number 43 (Wednesday, March 5, 2003)]
[Rules and Regulations]
[Pages 10365-10367]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-5129]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM244, Special Conditions No. 25-228-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, modified by Avcon Industries, Inc. These modified 
airplanes will have novel and unusual design features when compared to 
the

[[Page 10366]]

state of technology envisioned in the airworthiness standards for 
transport category airplanes. The modification incorporates the 
installation of dual Innovative Solutions and Support, Inc., Air Data 
Display Units, and a single Innovative Solutions and Support, Inc., 
Analog Interface Unit that performs critical functions. 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 February 20, 
2003. Comments must be received on or before April 4, 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. NM244, 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. NM244.

FOR FURTHER INFORMATION CONTACT: Mark Quam, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue, SW., Renton, Washington, 98055-4056; 
telephone (425) 227-2145; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA has determined that notice and opportunity for prior public 
comment are 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, the FAA invites 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 July 10, 2002, Avcon Industries, Inc., P.O. Box 748, Newton, 
Kansas 67144, applied for a supplemental type certificate (STC) to 
modify Learjet Model 24/25 series airplanes. These models are currently 
approved under Type Certificate No. A10CE. The Learjet model 24 series 
airplanes have two aft-mounted General Electric Turbojet engines, a 
maximum operating altitude of 45,000 feet, and carries a crew of two 
with a maximum of six passengers. The Learjet model 25 series airplanes 
have two aft-mounted General Electric Turbojet engines, a maximum 
operating altitude of 51,000 feet, and carries a crew of two with a 
maximum of eight passengers. The modification incorporates the 
installation of dual Innovative Solutions and Support, Inc. (IS&S) Air 
Data Display Units (ADDU) and a single IS&S Analog Interface Unit (AIU) 
that are replacements for the existing altimetry system. The dual IS&S 
ADDU and a single IS&S AIU system use 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) external to the airplane. This 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, 1992, Avcon Industries, Inc., 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 
Learjet Model 24/25 Series airplanes includes Sec.  21.29; 14 CFR part 
25 effective February 1, 1965, as amended by Amendments 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, 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 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(b)(2), Amendment 21-69, effective 
September 16, 1991.
    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 already 
included on Type Certificate Data Sheet (TCDS) A10CE to incorporate the 
same or similar novel or unusual design features, these special 
conditions would also apply to the other model under the provisions of 
Sec.  21.101(a)(1), Amendment 21-69, effective September 16, 1991.

Novel or Unusual Design Features

    The Learjet Model 24/25 Series airplanes modified by Avcon 
Industries, Inc., will incorporate installation of dual IS&S Air Data 
Display Units (ADDU), and a single IS&S Analog Interface Unit (AIU) 
that will perform critical functions. These advanced systems use 
electronics to a far greater extent than the original altimetry system 
and may be vulnerable to high-intensity radiated fields (HIRF) external 
to the airplane. The current airworthiness standards of

[[Page 10367]]

part 25 do not contain adequate or appropriate safety standards for the 
protection of this equipment from the adverse effects of HIRF. 
Accordingly, these systems are considered to be novel or unusual design 
features.

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, 
modified by Avcon Industries, Inc. These special conditions require 
that new sensitive 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 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 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
------------------------------------------------------------------------
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 Avcon Industries, Inc. 
Should Avcon Industries, Inc., 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 Sec.  21.101(a)(1), Amendment 21-69, effective 
September 16, 1991.

Conclusion

    This action affects only certain novel or unusual design features 
on Learjet Model 24/25 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 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 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 supplemental type certification basis for the Learjet Model 24/25 
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 February 20, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 03-5129 Filed 3-4-03; 8:45 am]
BILLING CODE 4910-13-U