[Federal Register Volume 70, Number 70 (Wednesday, April 13, 2005)]
[Rules and Regulations]
[Pages 19257-19259]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-7430]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. CE221, Special Condition 23-161-SC]


Special Conditions; Twin Commander Aircraft Models 690C, 690D, 
695, 695A, and 695B; Protection of Systems for 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 to Twin Commander Aircraft 
LLC. 19010 59th DR. NE. Arlington, WA. 98223 for a Supplemental Type 
Certificate for the Twin Commander Aircraft Models 690C, 690D, 695, 
695A, and 695B. These airplanes will have novel and unusual design 
features when compared to the state of technology envisaged in the 
applicable airworthiness standards. The novel and unusual design 
features include the installation of dual Innovative Solutions & 
Support (IS&S) Air Data Display Units (ADDU) for which the applicable 
regulations do not contain adequate or appropriate airworthiness 
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 the airworthiness 
standards applicable to these airplanes.

DATES: The effective date of these special conditions is April 13, 
2005.
    Comments must be received on or before May 13, 2005 for domestic, 
August 11, 2005 for foreign.

ADDRESSES: Comments may be mailed in duplicate to: Federal Aviation 
Administration, Regional Counsel, ACE-7, Attention: Rules Docket Clerk, 
Docket No. CE221, Room 506, 901 Locust, Kansas City, Missouri 64106. 
All comments must be marked: Docket No. CE221. 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: Wes Ryan, Aerospace Engineer, 
Standards Office (ACE-110), Small Airplane Directorate, Aircraft 
Certification Service, Federal Aviation Administration, 901 Locust, 
Room 301, Kansas City, Missouri 64106; telephone (816) 329-4127.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice and 
opportunity for prior public comment hereon are impracticable because 
these procedures would significantly delay issuance of the approval 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.

Comments Invited

    Interested persons are invited to submit such written data, views, 
or arguments, as they may desire. Communications should identify the 
regulatory docket or notice number and be submitted in duplicate to the 
address specified above. All communications received on or before the 
closing date for comments will be considered by the Administrator. The 
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 this notice must include a self-
addressed, stamped postcard on which the following statement is made: 
``Comments to Docket No. CE221.'' The postcard will be date stamped and 
returned to the commenter.

Background

    On April 5, 2004, Twin Commander Aircraft LLC. 19010 59th DR NE. 
Arlington, WA. 98223, made application to the FAA for a new 
Supplemental Type Certificate for the Twin Commander Aircraft Models 
690C, 690D, 695, 695A, and 695B. The Twin Commander Aircraft Models of 
concern are approved under TCDS No. 2A4. The proposed modification 
incorporates a novel or unusual design feature, a digital air data 
computer, which may be vulnerable to HIRF external to the airplane.

Type Certification Basis

    Under the provisions of 14 CFR part 21, Sec.  21.101, Twin 
Commander Aircraft LLC. must show that the Twin Commander Aircraft 
Models 690C, 690D, 695, 695A, and 695B meet the following provisions, 
or the applicable regulations in effect on the date of application for 
the change. For those areas modified or impacted by the installation of 
the IS&S ADDU (Air Data Display Unit) system, the following paragraphs 
as amended by Amendments 23-1 through 23-54 must be complied with: 
23.305, 23.307, 23.365, 23.603, 23.609, 23.611, 23.613, 23.625, 23.627, 
23.771, 23.773, 23.777, 23.1301, 23.1303, 23.1309, 23.1311, 23.1321, 
23.1322, 23.1331, 23.1335, 23.1351, 23.1357, 23.1359, 23.1361, 23.1365, 
23.1367, 23.1381, 23.1431, 23.1529, 23.1541, 23.1543, 23.1581 and the 
special conditions adopted by this rulemaking action. For systems that 
are not modified or impacted by the installation, the original 
certification basis listed on TCDS No. 2A4 are still applicable.

Discussion

    If the Administrator finds that the applicable airworthiness 
standards do not contain adequate or appropriate safety standards 
because of novel or unusual design features of an airplane, special 
conditions are prescribed under the provisions of Sec.  21.16.
    Special conditions, as appropriate, as defined in Sec.  11.19, are 
issued in accordance with Sec.  11.38 after public notice and become 
part of the type certification basis in accordance with Sec.  21.101.
    Special conditions are initially applicable to the models for which 
they are issued. Should the applicant apply 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, 
the special conditions would also apply to the other model under the 
provisions of Sec.  21.101.

Novel or Unusual Design Features

    Twin Commander Aircraft LLC. plans to incorporate certain novel and 
unusual design features into an airplane for which the airworthiness 
standards do not contain adequate or appropriate

[[Page 19258]]

safety standards for protection from the effects of HIRF. These 
features include the addition of a digital Air Data computer, which may 
be susceptible to the HIRF environment, that were not envisaged by the 
existing regulations for this type of airplane.

Protection of Systems From High Intensity Radiated Fields (HIRF)

    Recent advances in technology have given rise to the application in 
aircraft designs of advanced electrical and electronic systems that 
perform functions required for continued safe flight and landing. Due 
to the use of sensitive solid-state advanced components in analog and 
digital electronics circuits, these advanced systems are readily 
responsive to the transient effects of induced electrical current and 
voltage caused by the HIRF. The HIRF can degrade electronic systems 
performance by damaging components or upsetting system functions.
    Furthermore, the HIRF environment has undergone a transformation 
that was not foreseen when the current requirements were developed. 
Higher energy levels are radiated from transmitters that are used for 
radar, radio, and television. Also, the number of transmitters has 
increased significantly. There is also uncertainty concerning the 
effectiveness of airframe shielding for HIRF. Furthermore, coupling to 
cockpit-installed equipment through the cockpit window apertures is 
undefined.
    The combined effect of the technological advances in airplane 
design and the changing environment has resulted in an increased level 
of vulnerability of electrical and electronic systems required for the 
continued safe flight and landing of the airplane. Effective measures 
against the effects of exposure to HIRF must be provided by the design 
and installation of these systems. The accepted maximum energy levels 
in which civilian airplane system installations must be capable of 
operating safely are based on surveys and analysis of existing radio 
frequency emitters. These special conditions require that the airplane 
be evaluated under these energy levels for the protection of the 
electronic system and its associated wiring harness. These external 
threat levels, which are lower than previous required values, are 
believed to represent the worst case to which an airplane would be 
exposed in the operating environment.
    These special conditions require qualification of systems that 
perform critical functions, as installed in aircraft, to the defined 
HIRF environment in paragraph 1 or, as an option to a fixed value using 
laboratory tests, in paragraph 2, as follows:
    (1) The applicant may demonstrate that the operation and 
operational capability of the installed electrical and electronic 
systems that perform critical functions are not adversely affected when 
the aircraft is exposed to the HIRF environment defined:

------------------------------------------------------------------------
                                                         Field strength
                                                           (volts per
                       Frequency                             meter)
                                                       -----------------
                                                          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 root-mean-square
  (rms) values.

or,
    (2) The applicant may demonstrate by a system test and analysis 
that the electrical and electronic systems that perform critical 
functions can withstand a minimum threat of 100 volts per meter, 
electrical field strength, from 10 kHz to 18 GHz. When using this test 
to show compliance with the HIRF requirements, no credit is given for 
signal attenuation due to installation.
    The applicant, for approval by the FAA, to identify either 
electrical or electronic systems that perform critical functions, must 
perform a preliminary hazard analysis. The term ``critical'' means 
those functions, whose failure would contribute to, or cause, a failure 
condition that would prevent the continued safe flight and landing of 
the airplane. The systems identified by the hazard analysis that 
perform critical functions are candidates for the application of HIRF 
requirements. A system may perform both critical and non-critical 
functions. Primary electronic flight display systems, and their 
associated components, perform critical functions such as attitude, 
altitude, and airspeed indication. The HIRF requirements apply only to 
critical functions.
    Compliance with HIRF requirements may be demonstrated by tests, 
analysis, models, similarity with existing systems, or any combination 
of these. Service experience alone is not acceptable since normal 
flight operations may not include an exposure to the HIRF environment. 
Reliance on a system with similar design features for redundancy as a 
means of protection against the effects of external HIRF is generally 
insufficient since all elements of a redundant system are likely to be 
exposed to the fields concurrently.

Applicability

    As discussed above, these special conditions are applicable to the 
Twin Commander Aircraft Models 690C, 690D, 695, 695A, and 695B. Should 
Twin Commander Aircraft LLC. apply at a later date for a supplemental 
type certificate to modify any other model on the same type certificate 
to incorporate the same novel or unusual design feature, the 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 one model of airplane. 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 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 23

    Aircraft, Aviation safety, Signs and symbols.

[[Page 19259]]

PART 23--AIRWORTHINESS STANDARDS; NORMAL, UTILITY, ACROBATIC, AND 
COMMUTER CATEGORY AIRPLANES

Citation

0
The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113 and 44701; 14 CFR 21.16 and 
21.101; and 14 CFR 11.38 and 11.19.

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 type certification basis for the Twin Commander Aircraft Models 
690C, 690D, 695, 695A, and 695B modified by Twin Commander Aircraft 
LLC. to add a digital Air Data computer.
    1. Protection of Electrical and Electronic Systems from High 
Intensity Radiated Fields (HIRF). Each system that performs critical 
functions must be designed and installed to ensure that the operations, 
and operational capabilities of these systems to perform critical 
functions, are not adversely affected when the airplane is exposed to 
high intensity radiated electromagnetic 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 Kansas City, Missouri on April 1, 2005.
David R. Showers,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-7430 Filed 4-12-05; 8:45 am]
BILLING CODE 4910-13-P