[Federal Register Volume 69, Number 128 (Tuesday, July 6, 2004)]
[Rules and Regulations]
[Pages 40537-40538]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-15037]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM282 Special Conditions No. 25-267-SC]


Special Conditions: Learjet Model 35, 35A, 36, and 36A 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 Learjet Model 35, 35A, 
36, and 36A series airplanes modified by Flight Test Associates. These 
modified 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 installation of a Honeywell Model BA-250 altimeter 
indicator and a Model AM-250 barometric altimeter. 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 June 3, 2004. 
Comments must be received on or before August 5, 2004.

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. NM282, 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. NM282.

FOR FURTHER INFORMATION CONTACT: Mr. Steve Edgar, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone 
(425) 227-2025; facsimile (425) 227-1149.

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, 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 4:00 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 December 19, 2003, Flight Test Associates, Incorporated, of 
Mojave, California, applied to the FAA, Los Angeles Aircraft 
Certification Office, for a supplemental type certificate (STC) to 
modify Learjet Model 35, 35A, 36, and 36A series airplanes. These 
models are currently approved under Type Certificate No. A10CE. The 
proposed modification incorporates installation of the digital 
Honeywell Model BA-250 altimeter indicator and Model AM-250 barometric 
altimeter as primary altimeters. The information presented by this 
equipment is flight critical. The digital altimeters installed in these 
airplanes 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, Flight Test Associates must 
show that the Learjet Model 35, 35A, 36, and 36A 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 regulations incorporated by reference in Type Certificate No. 
A10CE include 14 CFR part 25 as amended by Amendments 25-2, 25-4, 25-7, 
25-10, and 25-18.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25, as amended) do not contain adequate 
or appropriate safety standards for the modified Learjet Model 35, 35A, 
36, and 36A 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, 35A, 36, and 36A 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 Flight Test Associates apply at a later date 
for a supplemental type certificate to modify any other model included 
on the same type certificate to incorporate the 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.

[[Page 40538]]

Novel or Unusual Design Features

    As noted earlier, the Learjet Model 35, 35A, 36, and 36A series 
airplanes modified by Flight Test Associates will incorporate new dual 
primary altimeters that will perform critical functions. These systems 
may be vulnerable to HIRF 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, 35A, 36, and 36A series 
airplanes modified by Flight Test Associates. These special conditions 
require that new primary altimeters 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 is shown with either HIRF protection 
special condition 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 
identifed in the following table 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
2GHz-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 35, 35A, 36, and 36A series airplanes modified by Flight 
Test Associates. Should Flight Test Associates apply at a later date 
for an STC 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 as 
under the provisions of 14 CFR 21.101.

Conclusion

    This action affects only certain novel or unusual design features 
on the Learjet Model 35, 35A, 36, and 36A series airplanes modified by 
Flight Test Associates. 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 record keeping 
requirements.


0
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 the Learjet Model 35, 
35A, 36, and 36A series airplanes modified by Flight Test Associates:
    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 June 3, 2004.
Franklin Tiangsing,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 04-15037 Filed 7-2-04; 8:45 am]
BILLING CODE 4910-13-P