[Federal Register Volume 61, Number 84 (Tuesday, April 30, 1996)]
[Rules and Regulations]
[Pages 18939-18941]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-10673]



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Rules and Regulations
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Federal Register / Vol. 61, No. 84 / Tuesday, April 30, 1996 / Rules 
and Regulations

[[Page 18939]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. 131CE, Special Condition 23-ACE-86]


Special Conditions; Cessna Model 425 Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

-----------------------------------------------------------------------

SUMMARY: These special conditions are issued for the Cessna Model 425 
airplanes modified by Modern Avionics, Inc., Eden Prairie, Minnesota. 
These airplanes 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 on 
publication in the Federal Register. Comments must be received on or 
before May 30, 1996.

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. 131CE, Room 1558, 601 East 
12th Street, Kansas City, Missouri 64106. All comments must be marked: 
Docket No. 131CE. 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. 131CE.'' The 
postcard will be date stamped and returned to the commenter.

Background

    On March 8, 1996, Modern Avionics, Inc., 10000 Flying Cloud Drive, 
Eden Prairie, Minnesota 55347, made an application to the FAA for a 
supplemental type certificate (STC) for the Cessna Model 425 airplanes. 
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 Cessna Model 425 Airplanes is 
given in Type Certification Data Sheet No. A7CE 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 
rulemaking 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, designed 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, effective 
October 25, 1989, after public notice, as required by Secs. 11.28 and 
11.29(b), and become a part of the type certification basis in 
accordance with Sec. 21.101(b)(2).
    Modern Avionics, Inc., 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

[[Page 18940]]

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 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 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, 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.

Conclusion

    In view of the design features discussed for the Cessna Model 425 
Airplanes, 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 Models 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: 49 U.S.C. 106(g); 40113, 44701, 44702, and 44704; 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 Cessna Model 425 
Airplanes:
    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.


[[Page 18941]]


    Issued in Kansas City, Missouri on April 15, 1996.
Henry A. Armstrong,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-10673 Filed 4-29-96; 8:45 am]
BILLING CODE 4910-13-M