[Federal Register Volume 60, Number 124 (Wednesday, June 28, 1995)]
[Rules and Regulations]
[Pages 33332-33333]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-15889]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. 125CE, Special Condition 23-ACE-81]


Special Conditions; Twin Commander Model 695 Airplane

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 Twin Commander 
Model 695 airplane modified by Garrett Aviation Services, Augusta, 
Georgia. This airplane will have novel and unusual design features when 
compared to the state of technology envisaged in the applicable 
airworthiness standards. These novel and unusual design features 
include the installation of electronic displays 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.

EFFECTIVE DATE: The effective date of these special conditions is June 
28, 1995. Comments must be received on or before July 28, 1995.

ADDRESSES: Comments may be mailed in duplicate to: Federal Aviation 
Administration, Office of the Assistant Chief Counsel, ACE-7, 
Attention: Rules Docket Clerk, Docket No. 125CE, Room 1558, 601 East 
12th Street, Kansas City, Missouri 64106. All comments must be marked: 
Docket No. 125CE. 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: Ervin Dvorak, Aerospace Engineer, 
Standards Office (ACE-110), Small Airplane Directorate, Aircraft 
Certification Service, Federal Aviation Administration, 601 East 12th 
Street, Kansas City, Missouri 64106; telephone (816) 426-6941.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety, and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
these special conditions.
    Interested persons are invited to submit such written data, views, 
or arguments as they may desire. Communications should identify the 
regulatory docket and special conditions 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. These special conditions may be changed in light of the 
comments received. All comments submitted will be available in the 
rules docket for examination by interested parties, 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. Persons wishing the FAA to 
acknowledge receipt of their comments, submitted in response to this 
request, must include a self-addressed and stamped postcard on which 
the following statement is made: ``Comments to Docket No. 125CE.'' The 
postcard will be date stamped and returned to the commenter.

Background

    On October 31, 1994, Garrett Aviation Services, 1550 Hangar Road, 
Augusta, Georgia 30906, made an application to the FAA for a 
supplemental type certificate (STC) for the Twin Commander Model 695 
airplane. The proposed modification incorporates a novel or unusual 
design feature, such as digital avionics consisting of an electronic 
flight instrument system (EFIS), that is vulnerable to HIRF external to 
the airplane.

Type Certification Basis

    The type certification basis for the Twin Commander Model 695 
Airplane is given in Type Certification Data Sheet No. 2A4 plus the 
following:
    Sec. 23.1301 of Amendment 23-20; Secs. 23.1309, 23.1311, and 
23.1321 of Amendment 23-41 and Sec. 23.1322 of Amendment 23-43; 
exemptions, if any; and the special conditions adopted by this remaking 
action.
Discussion

    The FAA may issue and amend special conditions, as necessary, as 
part of the type certification basis if the Administrator finds that 
the airworthiness standards, designated according to Sec. 21.101(b), 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 to establish a level of 
safety equivalent to that established in the regulations. Special 
conditions are normally issued according to Sec. 11.49, after public 
notice, as required by Secs. 11.28 and 11.29(b), effective October 14, 
1980, and become a part of the type certification basis in accordance 
with Sec. 21.101(b)(2).
    Garrett Aviation Services, plans to incorporate certain novel and 
unusual design features into an airplane for which the airworthiness 
standards do not contain adequate or appropriate safety standards for 
protection from the effects of HIRF. These features include electronic 
systems, which are 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 [[Page 33333]] 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 below:

                       Field Strength Volts/Meter                       
------------------------------------------------------------------------
                      Frequency                         Peak     Average
------------------------------------------------------------------------
10-100 KHz..........................................        50        50
100-500.............................................        60        60
500-2000............................................        70        70
2-30 MHz............................................       200       200
30-70...............................................        30        30
70-100..............................................        30        30
100-200.............................................       150        33
200-400.............................................        70        70
400-700.............................................      4020       935
700-1000............................................      1700       170
1-2 GHz.............................................      5000       990
2-4.................................................      6680       840
4-6.................................................      6850       310
6-8.................................................      3600       670
8-12................................................      3500      1270
12-18...............................................      3500       360
18-40...............................................      2100       750
------------------------------------------------------------------------

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, 
peak 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.
    A preliminary hazard analysis must be performed by the applicant, 
for approval by the FAA, to identify electrical and/or electronic 
systems that perform critical functions. 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, similarly 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.

Conclusion

    In view of the design features discussed for the Twin Commander 
Model 695 Airplane, the following special conditions are issued. This 
action is not a rule of general applicability and affects only those 
applicants who apply to the FAA for approval of these features on these 
airplanes.
    The substance of these special conditions has been subject to the 
notice and public comment procedure in several prior rulemaking 
actions. For example, the Dornier 228-200 (53 FR 14782, April 26, 
1988), the Cessna Model 525 (56 FR 49396, September 30, 1991), and the 
Beech Model 200, A200, and B200 airplanes (57 FR 1220, January 13, 
1992). It is unlikely that additional public comment would result in 
any significant change from those special conditions already issued and 
commented on. For these reasons, and because a delay would 
significantly affect the applicant's installation of the system and 
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 without notice. Therefore, these special conditions are 
being made effective upon publication in the Federal Register. However, 
as previously indicated, interested persons are invited to comment on 
these special conditions if they so desire.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols

Citation

    The authority citation for these special conditions is as follows:

    Authority: Secs. 313(a), 601, and 603 of the Federal Aviation 
Act of 1958; as amended (49 U.S.C. 1354(a), 1421, and 1423); 49 
U.S.C. 106(g); 14 CFR 21.16 and 21.101; and 14 CFR 11.28 and 11.49.

Adoption of 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 the modified Twin Commander Model 695 
airplane:
    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 June 1, 1995.
Henry A. Armstrong,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-15889 Filed 6-27-95; 8:45 am]
BILLING CODE 4910-13-M