[Federal Register Volume 60, Number 105 (Thursday, June 1, 1995)]
[Proposed Rules]
[Pages 28547-28550]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-13397]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-93; Special Conditions No. 25-ANM-99]


Special Condition: Cessna Aircraft Company, Model 750 (Citation 
X) Airplane, High-Intensity Radiated Fields

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special condition.

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SUMMARY: This special condition for the Cessna Aircraft Company 
(Cessna) is issued for the Model 750 (Citation X) airplane. This new 
airplane will utilize new avionics/electronic systems that provide 
critical data to the flightcrew. The applicable regulations do not 
contain adequate or appropriate safety standards for the protection of 
these systems from the effects of high-intensity radiated fields. This 
special condition contains the additional safety standards that the 
Administrator considers necessary to establish a level of safety 
equivalent to that established by the existing airworthiness standards.

EFFECTIVE DATE: July 3, 1995.

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 (206) 221-2145, facsimile 
(206) 227-1320.

SUPPLEMENTARY INFORMATION:

Background

    On October 15, 1991, Cessna Aircraft Company (Cessna), 6030 Cessna 
Blvd., P.O. Box 7704, Wichita, KS 67277-7704, applied for a new type 
certificate in the transport airplane category for the Model 750 
(Citation X) airplane. The Cessna Model 750 is a T-tail, low swept 
wing, medium-sized business jet powered by two GMA-3007C turbofan 
engines mounted on pylons extending from the aft fuselage. Each engine 
will be capable of delivering 6,000 pounds thrust. The flight controls 
will be powered and capable of manual reversion. The airplane has a 
seating capacity of up to twelve passengers, and a maximum takeoff 
weight of 31,000 pounds. [[Page 28548]] 

Type Certification Basis

    Under the provisions of Sec. 21.17 of the FAR, Cessna must show, 
except as provided in Sec. 25.2, that the Model 750 (Citation X) meets 
the applicable provisions of part 25, effective February 1, 1965, as 
amended by Amendments 25-1 through 25-74 and Amendment 25-80. In 
addition, the proposed certification basis for the Model 750 includes 
part 34, effective September 10, 1990, plus any amendments in effect at 
the time of certification; and part 36, effective December 1, 1969, as 
amended by Amendment 36-1 through the amendment in effect at the time 
of certification. No exemptions are anticipated. This special condition 
will form an additional part of the type certification basis.
    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 Cessna Model 750 because of a 
novel or unusual design feature, 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, as appropriate, are issued in accordance with 
Sec. 11.49 of the FAR after public notice, as required by Secs. 11.28 
and 11.29, and become part of the type certification basis in 
accordance with Sec. 21.17(a)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The Model 750 incorporates new avionics/electronic installations, 
including a digital Electronic Flight Instrument System (EFIS), Air 
data System, Attitude and Heading Reference System (AHRS), Navigation 
and Communication System, Autopilot System, and a Full Authority 
Digital Engine Control (FADEC) system that controls critical engine 
parameters. These systems may be vulnerable to high-intensity radiated 
fields external to the airplane.

Discussion

    At the time that Cessna applied for type certification of the 
Cessna Model 750 (Citation X) airplane, the existing lightning 
protection airworthiness certification requirements were insufficient 
to provide an acceptable level of safety for new technology avionics 
and electronic systems. The two existing regulations that specifically 
pertained to lightning were Sec. 25.581 (the airframe in general), and 
Sec. 25.954 (fuel system protection). There were, however, no 
regulations that specifically addressed protection of electrical and 
electronic systems from lightning.
    On March 29, 1994, the FAA published in the Federal Register Notice 
of Proposed Special Conditions No. SC-94-1-NM (59 FR 14571) for the 
Cessna Model 750 (Citation X). These special conditions were proposed 
requirements to protect the airplane systems from the effects of 
lightning and high-intensity radiated fields (HIRF). Cessna, commenting 
to the docket by letter, noted that there were differences in the 
preamble language from the language used in issue papers that discussed 
the proposed method of compliance with the special conditions. The FAA 
agreed. Although the special conditions proposed were not changed from 
the original notice, the methods of compliance discussed in the issue 
papers that preceded the original notice were, in fact, different in 
certain respects than the methods of compliance discussed in the 
original notice. The FAA inadvertently left out Cessna's proposed 
alternative methods of complying with the proposed special conditions. 
As the methods of compliance proposed by Cessna deviate in certain 
respects from previous methods of compliance with the proposed special 
conditions, the FAA agreed these methods should also be made available 
for the public record and comment as well. Therefore, Notice SC-94-1-NM 
was republished in the Federal Register on September 12, 1994, as 
Notice SC-94-1A-NM (59 FR 46775) in its entirety, including Cessna's 
proposed alternative methods of compliance with the special conditions.
    The FAA agrees with Cessna's proposed alternative method of testing 
and evaluation of the effects of lightning on the installed airplane 
systems when complying with the proposed special conditions. However, 
lightning protection is no longer considered a novel or unusual design 
feature relative to the regulations, as Amendment 25-80, effective May 
21, 1994, was added to 14 CFR part 25 of the FAR (59 FR 22116, April 
28, 1994). The lightning special condition differs from the rule in 
that the definitions of critical and essential functions are retained 
as a separate paragraph (i.e. item 3 in the notice). The rule also 
provides approaches to compliance for designing and verifying lightning 
protection in Sec. 25.1316(c) that would be no different than the 
approaches to compliance for the special conditions.
    As there is no longer a need for lightning special conditions, the 
proposed lightning special condition has been removed from this final 
special condition and Sec. 25.1316, as adopted by Amendment 25-80, will 
be added to the Cessna 750 certification basis as authorized under 
Sec. 21.17(a)(1)(i). Cessna's proposed method of testing and evaluation 
of the effects of lightning on the installed airplane systems for 
compliance with the lightning special condition can be utilized when 
complying with Sec. 25.1316, as the intent of the lightning special 
condition and Sec. 25.1316 are identical.
    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 electrical and electronic 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, a special 
condition is needed for the Cessna Model 750, to require that new 
technology electrical and electronic systems, such as the EFIS, FADEC, 
AHRS, etc., be designed and installed to preclude component damage and 
interruption of function due to both the direct and indirect effects 
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, the FAA considers that 
an adequate level of protection exists when compliance with the HIRF 
protection special condition is shown with either paragraphs 1 or 2 
below:
    1. A minimum threat of 100 volts per meter peak electric field 
strength from 10 KHz to 18 GHz.
    a. The threat must be applied to the system elements and their 
associated [[Page 28549]] 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.


------------------------------------------------------------------------
                                                      Peak (V/   Average
                      Frequency                          M)       (V/M) 
------------------------------------------------------------------------
10 KHz-100 KHz......................................        50        50
100 KHz-500 KHz.....................................        60        60
500 KHz-2000 KHz....................................        70        70
2 MHz-30 MHz........................................       200       200
30 MHz-100 MHz......................................        30        30
100 MHz-200 MHz.....................................       150        33
200 MHz-400 MHz.....................................        70        70
400 MHz-700 MHz.....................................     4,020       935
700 MHz-1000 MHz....................................     1,700       170
1 GHz-2 GHz.........................................     5,000       990
2 GHz-4 GHz.........................................     6,680       840
4 GHz-6 GHz.........................................     6,850       310
6 GHz-8 GHz.........................................     3,600       670
8 GHz-12 GHz........................................     3,500     1,270
12 GHz-18 GHz.......................................     3,500       360
18 GHz-40 GHz.......................................     2,100       750
------------------------------------------------------------------------


    Cessna's market for the Model 750 Citation X includes, at the 
present time, two European JAA member countries. Consequently, Cessna 
intends to pursue certification to meet the European JAA requirements 
as well as the FAA requirements. To reduce the testing required, Cessna 
proposes to test to an environment that combines a proposed FAA 
certification environment (from the SAE AE4R Subcommittee) and a 
proposed JAA certification environment (from EUROCAE WG-33) to form a 
``worst case'' certification environment. Cessna's proposed environment 
consists of the following:

    Where the combined proposed certification environment is less than 
100 volts per meter, Cessna would test to the proposed certification 
environment (JAA or FAA, whichever is higher). Where the combined 
environment is greater than 100 volts per meter, Cessna would test to 
the proposed JAA environment (less aircraft attenuation above 200 MHz). 
The aircraft attenuation would be established by the results of full 
vehicle tests conducted by Cessna on Model 650, Citation III, and 
Citation VII aircraft. Cessna's proposed Model 750 HIRF certification 
environment is as follows:

  Proposed Cessna 750 (Citation X (CX)) HIRF Certification Environment  
------------------------------------------------------------------------
                               Proposed FAA   Proposed JAA              
                              certification  certification   Proposed CX
       Frequency (HZ)          environment    environment    environment
                                (peak/avg)     (peak/avg)    (peak/avg) 
------------------------------------------------------------------------
10K-500K....................  50/50          40/40          50/50       
500K-2M.....................  40/40          40/40          40/40       
2M-30M......................  100/100        100/100        100/100     
30M-100M....................  20/20          20/20          20/20       
100M-200M...................  50/30          50/30          50/30       
200M-400M...................  70/70          70/70          70/70       
400M-700M...................  1520/750       700/30         700/30      
700M-1G.....................  1300/170       1300/70        1300/70     
1G-2G.......................  2500/180       2500/160       2500/160    
2G-4G.......................  3500/360       3500/240       3500/240    
4G-6G.......................  6800/280       3200/280       3200/280    
6G-8G.......................  1800/330       800/330        800/330     
8G-12G......................  3500/215       3500/330       3500/330    
12G-18G.....................  1700/270       1700/180       1700/180    
------------------------------------------------------------------------

Discussion of Comments

    There were no comments received in response to Notice SC-94-1-NM 
other than those submitted by Cessna, as discussed earlier in this 
document. No comments were received in response to Supplemental Notice 
SC-94-1A-NM.

The Federal Aviation Administration's Analysis/Summary

    The FAA does not agree with Cessna's proposed alternative method of 
compliance (i.e., the proposed CX threat environment) for the 
evaluation of the effects of HIRF on the installed airplane systems. 
The FAA has not formally adopted any of the certification environments 
proposed by Cessna listed above. The latest published FAA policy that 
defines the external environment acceptable for airplane testing is 
dated July 29, 1992, and is reflected earlier in the preamble to these 
special conditions. If Cessna wishes to reduce testing by combining the 
FAA and JAA environments, Cessna should test to the higher of the 
values given in the environment tables that have been adopted by the 
FAA and JAA. It should be noted that frequencies above 18 GHz should be 
used only if the pass/fail criteria are not met in the 12-18 GHz range, 
or if the system is designed to operate in the range from 18-40 GHz.
    The FAA's option of testing using 100 volts per meter threat from 
10 KHz to 18 GHz requires that this treat be applied to the systems 
elements and associated wiring without the benefit of airframe 
shielding. The 100 volts per meter test can be established by systems 
tests and analysis acceptable to the FAA.
    In summary, the FAA has determined that Cessna must utilize the 
FAA's HIRF envelop (the first HIRF envelope and not the proposed SAE 
AE4R envelop) or may combine the FAA HIRF envelope and the JAA envelope 
and test to the greater values.
    As discussed earlier in this document, the special conditions are 
applicable initially to the Model 750. Should Cessna apply at a later 
date for a change to the type certificate to include another model 
incorporating that same novel or unusual design feature, the special 
conditions would apply to that model as well, under the provisions of 
Sec. 21.101(a)(1).

Conclusion

    This action affects only certain design features on the Cessna 
Model 750 (Citation X) airplane. It is not a rule of general 
applicability and affects only the manufacturer who applied to the FAA 
for approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and record keeping 
requirements.

    The authority citation for these special conditions is as follows:

    Authority 49 U.S.C. app. 1344, 1348(c), 1352, 1354(a), 1355, 
1421 through 1431, 1502, 1651(b)(2), 42 U.S.C. 1857f-10, 4321 et 
seq.; E.O. 11514; and 49 U.S.C. 106(g).

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special condition is issued as part of the 
type certification basis for the Cessna Model 750 (Citation X) series 
airplanes.
    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 this special condition, 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 28550]] Issued in Renton, Washington, on May 8, 1995.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-13397 Filed 5-31-95; 8:45 am]
BILLING CODE 4910-13-M