[Federal Register Volume 59, Number 175 (Monday, September 12, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-22017]


[[Page Unknown]]

[Federal Register: September 12, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 25

[Docket No. NM-93; Notice No. SC-94-1A-NM]

 

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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Supplemental notice of proposed special conditions.

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

SUMMARY: This notice proposes special conditions for the Cessna 
Aircraft Company (Cessna), 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 lightning and high-intensity radiated 
fields. These proposed special conditions contain the additional safety 
standards that the Administrator considers necessary to establish a 
level of safety equivalent to that established by the existing 
airworthiness standards.

DATES: Comments must be received on or before October 27, 1994.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Office of the Assistant Chief Counsel, 
Attn: Rules Docket (ANM-7), Docket No. NM-93, 1601 Lind Avenue SW., 
Renton, Washington, 98055-4056; or delivered in duplicate to the Office 
of the Assistant Chief Counsel at the above address. Comments must be 
marked: Docket No. NM-93. 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: Mark Quam, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056, (206) 
227-2145.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of 
these proposed special conditions by submitting 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 
before further rulemaking action is taken on these proposals. The 
proposals contained in this notice may be changed in light of comments 
received. All comments submitted 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. Persons wishing the FAA to acknowledge receipt of their 
comments submitted in response to this notice must submit with those 
comments a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to Docket No. NM-93.'' The postcard will 
be date stamped and returned to the commenter.

Background

    On March 29, 1994, the FAA published in the Federal Register (59 FR 
14571) proposed special conditions for the Cessna Model 750 (Citation 
X). These special conditions are 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 these special conditions. The FAA agrees. Although the 
special conditions proposed herein have 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 alternate 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 
agrees these methods should also be made available for the public 
record and comment as well.
    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.

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 1965, as 
amended by Amendments 25-1 through 25-74. 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. The special conditions 
that may be developed as a result of this notice will form an 
additional part of the type certification basis. In addition, the 
certification basis may include other special conditions that are not 
relevant to these proposed special conditions.
    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).

Novel or Unusual Design Features

    The Model 750 incorporates new avionic/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 lightning and high-
intensity radiated fields external to the airplane.

Discussion

    The existing lightning protection airworthiness certification 
requirements are insufficient to provide an acceptable level of safety 
with new technology avionic and electronic systems. There are two 
regulations that specifically pertain to lightning protection: one for 
the airframe in general (Sec. 25.581), and the other for fuel system 
protection (Sec. 25.954). There are, however, no regulations that deal 
specifically with protection of electrical and electronic systems from 
lightning. The loss of a critical function of these systems due to 
lightning would prevent continued safe flight and landing of the 
airplane. Although the loss of an essential function would not prevent 
continued safe flight and landing, it could significantly impact the 
safety level of the airplane.
    There is also 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, special 
conditions are proposed for the Cessna Model 750, which would 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 of lightning and HIRF.

Lightning

    To provide a means of compliance with these proposed special 
conditions, clarification of the threat definition of lightning is 
needed. The following ``threat definition,'' based on FAA Advisory 
Circular 20-136, Protection of Aircraft Electrical/Electronic Systems 
Against the Indirect Effects of Lightning, dated March 5, 1990, is 
proposed as a basis to use in demonstrating compliance with the 
lightning protection special condition, with the exception of the 
multiple burst environment, which has been changed to agree with the 
latest recommendation from the Society of Automotive Engineers (SAE) 
AE4L lightning committee.
    The lightning current waveforms (Components A, D, and H) defined 
below, along with the voltage waveforms in AC 20-53A, will provide a 
consistent and reasonable standard that is acceptable for use in 
evaluating the effects of lightning on the airplane. These waveforms 
depict threats that are external to the airplane. The effect of these 
threats on the airplane and its systems depends upon several factors, 
including installation configuration, materials, shielding, airplane 
geometry, etc. Therefore, tests (including tests on the completed 
airplane or an adequate simulation) and/or verified analyses need to be 
conducted in order to obtain the resultant internal threat to the 
installed systems. The electronic systems may then be evaluated with 
this internal threat in order to determine their susceptibility to 
upset and/or malfunction.
    To evaluate the induced effects to these systems, three 
considerations are required:
    1. First Return Stroke: (Severe Strike--Component A, or Restrike-
Component D). This external threat needs to be evaluated to obtain the 
resultant internal threat and to verify that the level of the induced 
currents and voltages is sufficiently below the equipment ``hardness'' 
level.
    2. Multiple Stroke Flash: (1/2 Component D). A lightning strike is 
often composed of a number of successive strokes, referred to as 
multiple strokes. Although multiple strokes are not necessarily a 
salient factor in a damage assessment, they can be the primary factor 
in a system upset analysis. Multiple strokes can induce a sequence of 
transients over an extended period of time. While a single event upset 
of input/output signals may not affect system performance, multiple 
signal upsets over an extended period of time (2 seconds) may affect 
the systems under consideration. Repetitive pulse testing and/or 
analysis needs to be carried out in response to the multiple stroke 
environment to demonstrate that the system response meets the safety 
objective. This external multiple stroke environment consists of 24 
pulses and is described as a single Component A followed by 23 randomly 
spaced restrikes of 1/2 magnitude of Component D (peak amplitude of 
50,000 amps). The 23 restrikes are distributed over a period of up to 2 
seconds according to the following constraints: (1) the minimum time 
between subsequent strokes is 10ms, and (2) the maximum time between 
subsequent strokes is 200ms. An analysis or test needs to be 
accomplished in order to obtain the resultant internal threat 
environment for the system under evaluation.
    3. Multiple Burst: (Component H). In-flight data-gathering projects 
have shown bursts of multiple, low amplitude, fast rates of rise, short 
duration pulses accompanying the airplane lightning strike process. 
While insufficient energy exists in these pulses to cause physical 
damage, it is possible that transients resulting from this environment 
may cause upset to some digital processing systems.
    The representation of this interference environment is a repetition 
of short duration, low amplitude, high peak rate of rise, double 
exponential pulses that represent the multiple bursts of current pulses 
observed in these flight data gathering projects. This component is 
intended for an analytical (or test) assessment of functional upset of 
the system. Again, it is necessary that this component be translated 
into an internal environmental threat in order to be used. This 
``Multiple Burst'' consists of repetitive Component H waveforms in 3 
sets of 20 pulses each. The minimum time between individual Component H 
pulses within a burst is 50 microseconds, the maximum is 1,000 
microseconds. The 3 bursts are distributed according to the following 
constraints: (1) the minimum period between bursts is 30ms, and (2) the 
maximum period between bursts is 300ms. The individual ``Multiple 
Burst'' Component H waveform is defined below.
    The following current waveforms constitute the ``Severe Strike'' 
(Component A), ``Restrike'' (Component D), ``Multiple Stroke'' (1/2 
Component D), and the ``Multiple Burst'' (Component H).
    These components are defined by the following double exponential 
equation:

i(t)=Io (e-at-e-bt).

where: t=time in seconds,

i=current in amperes, and

----------------------------------------------------------------------------------------------------------------
                                                                               Multiple                         
                                   Severe          Restrike(component D)      stroke(\1/           Multiple     
                            strike(component A)                             2\component D)    burst(component H)
----------------------------------------------------------------------------------------------------------------
Io, amp.............   =   218,810                109,405                 54,703             10,572             
a, sec-1............   =   11,354                 22,708                  22,708             187,191            
b, sec-1............   =   647,265                1,294,530               1,294,530          19,105,100         
                                                                                                                
This equation                                                                                                   
 produces the                                                                                                   
 following                                                                                                      
 characteristics:                                                                                               
                                                                                                                
    ipeak...........   =   200 KA                 100 KA                  50 KA              10 KA              
and,                                                                                                            
    (di/dt) max (amp/  =   1.4 X 10\11\           1.4 X 10\11\            0.7 X 10\11\       2.0 X 10\11\       
     sec).                                                                                                      
                       =   @t=0+sec               @t=0+sec                @t=0+sec           @t=0+sec           
    di/dt, (amp/sec)   =   1.0 X 10\11\           1.0 X 10\11\            0.5 X 10\11\                          
                       =   @t=.5s        @t=.25s        @t=.25s                      
    Action Integral    =   2.0 X 10\6\            0.25 X 10\6\            0.0625 X 10\6\                        
     (amp\2\ sec).                                                                                              
----------------------------------------------------------------------------------------------------------------

    It is Cessna's position that only damage tolerance testing of 
equipment that performs essential functions should be required using 
the procedures and conditions specified in DO-160C, Section 22 (change 
2). Pin injection or cable bundle testing would be required, but there 
should be no multi-strike or multi-burst requirement. Cessna proposes 
that to evaluate the induced effects of lightning to the systems under 
consideration, the following must be considered:

    Essential Functions: First Return Stroke
    Critical Functions: First Return Stroke; Multi-Stroke; Multi-Burst

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 has used 
criteria for compliance with the HIRF protection special condition 
shown in paragraphs 1 or 2 below:
    1. A mininum 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 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-70 MHz.......................................        30        30
70 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. This environment will consist 
of the following:
    Where the combined proposed certification environment is less than 
100 volts per meter, Cessna will test to the proposed certification 
environment (JAA or FAA, whichever is higher). Where the combined 
environment is greater than 100 volts per meter, Cessna will test to 
the proposed JAA environment (less aircraft attenuation above 200 MHz). 
The aircraft attenuation will 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  Proposed CX
                               certification  certification     threat  
        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 
------------------------------------------------------------------------

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 recordkeeping 
requirements.

    The authority citation for these proposed 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 Proposed Special Conditions

    Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for the Cessna Model 750 (Citation X) series airplanes.

1. Lightning Protection

    (a) 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 
lightning.
    (b) Each essential function of electrical or electronic systems or 
installations must be protected to ensure that the function can be 
recovered in a timely manner after the airplane has been exposed to 
lightning.

2. 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.

3. For the Purpose of These Special Conditions, the Following 
Definitions Apply

    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.
    Essential Functions. Functions whose failure could contribute to or 
cause a failure condition that would significantly impact the safety of 
the airplane or the ability of the flightcrew to cope with adverse 
operating conditions.

    Issued in Renton, Washington, on August 23, 1994.
Norman B. Martenson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 94-22017 Filed 9-9-94; 8:45 am]
BILLING CODE 4910-13-M