[Federal Register Volume 66, Number 51 (Thursday, March 15, 2001)]
[Rules and Regulations]
[Pages 15020-15022]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-6372]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM186, Special Conditions No. 25-175-SC]


Special Conditions: Learjet Model 55 and 55B 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 55 and 
55B airplanes modified by JetCorp. 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 the installation of 
dual Attitude Heading Reference Systems (ARHS) that provide air data 
input to both pilot and copilot flight instruments displaying critical 
flight parameters (attitude) to the flightcrew. The applicable 
airworthiness standards do not contain adequate or appropriate safety 
standards for the protection of these systems from the effects of high-
intensity radiated fields. The 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 7, 2001. 
Comments must be received on or before April 16, 2001.

ADDRESSES: Comments on these special conditions may be mailed in 
duplicate

[[Page 15021]]

to: Federal Aviation Administration, Transport Airplane Directorate, 
Attn: Rules Docket (ANM-114), Docket No. NM186, 1601 Lind Avenue SW., 
Renton, Washington, 98055-4056; or delivered in duplicate to the 
Transport Airplane Directorate at the above address. Comments must be 
marked: Docket No. NM186. 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: 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 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 rules docket or special 
conditions number and be submitted in duplicate to the address 
specified above. The Administrator will consider all communications 
received on or before the closing date for comments. These special 
conditions may be changed in light of the comments received. All 
comments received 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. 
Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to these special conditions must include a self-
addressed, stamped postcard on which the following statement is made: 
``Comments to Docket No. NM186.'' The postcard will be date stamped and 
returned to the commenter.

Background

    On November 28, 2000, JetCorp, 18152 Edison Avenue, Chesterfield, 
Missouri, 63005, applied for a supplemental type certificate (STC) to 
modify Learjet Model 55 and 55B airplanes listed on Type Certificate 
A10CE. The Lear 55 and 55B are twin-engine, executive type transports 
capable of carrying two flight crewmembers and eight passengers. Two 
aft-mounted Garrett TFE-731 engines power both models. The modification 
incorporates the installation of dual Rockwell Collins Attitude Heading 
Reference Systems (ARHS) 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, JetCorp must show that the 
Learjet Model 55 and 55B 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 55 and 55B airplanes includes 14 CFR part 25, 
dated February 1, 1965, as amended by Amendments 25-1, 25-3, 25-4, 25-
7, 25-10, 25-12, 25-18, 25-21, 25-30, and selected regulations under 
Amendments 25-11, 25-14, 25-15, 25-17, 25-20, 25-23, 25-36, 25-38, 25-
40, 25-42, and 25-43, as listed in Type Certificate Data Sheet 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 55 and 55B 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 55 and 55B airplanes must comply with the 
fuel vent and exhaust emission requirements of part 34 and the noise 
certification requirements of part 36.
    Special conditions, as defined in Sec. 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 JetCorp 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 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

    As noted earlier, the modified Learjet Model 55 and 55B airplanes 
will incorporate dual 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.

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 avionic/electronic 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 55 and 55B. These special 
conditions require that new avionic/electronic and electrical 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 paragraph 1, or paragraph 2, below:

[[Page 15022]]

    1. A minimum threat of 100 volts rms 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 following field 
strengths 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
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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
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 55 and 55B airplanes modified by JetCorp. Should JetCorp 
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 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 novel or unusual design features 
on Learjet Model 55 and 55B airplanes modified by JetCorp. 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 period 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 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 55 and 55B airplanes 
modified by JetCorp.
    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 March 7, 2001.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-6372 Filed 3-14-01; 8:45 am]
BILLING CODE 4910-13-P