[Federal Register Volume 59, Number 81 (Thursday, April 28, 1994)]
[Unknown Section]
[Page ]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-10169]


[Federal Register: April 28, 1994]


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Part X





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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14 CFR Part 25



Electrical and Electronic Systems Lightning Protection; Final Rule
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[Docket No. 25912; Amdt No. 25-80]
RIN 2120-AC81


Electrical and Electronic Systems Lightning Protection

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: This amendment adds a new standard for electrical and 
electronic systems installed in transport category airplanes. It is the 
result of increasing concern for the vulnerability of these systems to 
the indirect effects of lightning, and is intended to enhance safety by 
providing specific lightning protection requirements for electrical and 
electronic systems that perform essential or critical functions.

EFFECTIVE DATE: May 31, 1994.

FOR FURTHER INFORMATION CONTACT: Gene Vandermolen, FAA, Flight Test & 
Systems Branch, ANM-111, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98055-
4056; telephone (206) 227-2135.

SUPPLEMENTARY INFORMATION:

Background

    This amendment is based on Notice of Proposed Rulemaking (NPRM) No. 
89-15, which was published in the Federal Register on May 30, 1989 (54 
FR 23164).
    As discussed in the notice, concern for the vulnerability of 
airplane electronic systems to the effects of lightning has increased 
substantially over the past few years. The use of solid-state 
components in the design of electronic control systems in airplanes has 
made such systems potentially susceptible to transient effects of 
induced electrical current and voltage caused by a direct lightning 
strike to the airplane. These induced transient currents and voltages 
can degrade electronic system performance by damaging components or 
upsetting system functions. Component damage means a permanently 
altered electrical characteristic that can include dielectric 
breakdowns and effects from heat in semiconductor junctions, resistors, 
and component interconnections. Function upset refers to an impairment 
of system operation, either permanent or momentary (e.g., a change of 
digital or analog state), that includes logic changes in computer and 
processing systems, electronic engine and flight controls, and power 
generating and distribution systems.
    Another factor that has contributed to this increased concern is 
the reduced electromagnetic shielding afforded airplane electronic 
systems by advanced technology airframe materials. Some of these 
materials have no electrical conductivity and lightning strikes often 
puncture them, resulting in extensive damage and allowing lightning to 
attach to vulnerable electronic systems or components located within 
the airframe. Other materials, such as graphite-reinforced composites, 
have some electrical conductivity. Voltages induced by lightning 
current that flows in airframe components made of these composite 
materials are much higher than those in aluminum materials because the 
electrical resistance of composites is higher; therefore, such 
composites provide much less protection to the circuits and electronic 
systems in the airplane.
    There are two sections in 14 CFR part 25 that specifically pertain 
to lightning protection: one for the airframe in general (Sec. 25.581), 
and the other for the fuel system (Sec. 25.954). There are no 
regulations dealing specifically with lightning protection of 
electrical and electronic systems. The advent of advanced electronic 
systems in airplane designs submitted for FAA approval requires that 
additional consideration be given to protecting these systems from the 
effects of lighting strikes. Although Sec. 25.581(a) (structures 
subpart) requires that an airplane be protected against catastrophic 
effects of lighting, and Sec. 25.1309(a) states that required systems 
must operate properly in all environmental conditions, it has been 
determined that the existing lightning protection requirements are not 
adequate for advanced electronic systems.
    In recent type certification programs involving advanced electronic 
systems, such as those used in the Airbus A320, Boeing 747-400, and 
Douglas MD-11 airplanes, the FAA has adopted special conditions to 
provide an adequate level of safety.
    Since trends indicate that future airplane designs will incorporate 
similar systems, the FAA has determined that a change in the design 
standards of part 25 is necessary.

Discussion of Comments

    The following discussion summarizes the comments received from the 
public, industry, foreign authorities, and manufacturers in response to 
Notice 89-15.
    Several commenters request clarification as to what constitutes 
critical and essential functions.
    The terms ``critical'' and ``essential'' originated when attempts 
were made to classify failure conditions in accordance with 
Sec. 25.1309. This regulation requires that systems be designed so that 
the occurrence of any failure condition that would prevent the 
continued safe flight and landing of the airplane is extremely 
improbable. The function affected by such a failure condition is deemed 
``critical.'' Additionally, Sec. 25.1309 requires that systems be 
designed so that the occurrence of any other failure condition that 
would reduce the capability of the airplane or the ability of the crew 
to cope with adverse operating conditions is improbable. The function 
affected by such a failure condition is deemed ``essential.'' The 
combination of systems or system redundancy required to meet these 
reliability requirements is determined by conducting a preliminary 
hazard analysis or criticality assessment. Examples of systems that 
perform critical functions are full authority electronic engine 
controls, electronic primary flight controls, primary flight displays, 
and electronic stability augmentation. Examples of systems that perform 
essential functions are communications systems, navigation systems, and 
flight management systems.
    One commenter considers the lightning protection requirements to be 
unclear when applied to individual subsystems prior to installation in 
the airplane, and recommends that the relationship between the airframe 
manufacturer and the subsystem supplier to clarified. The commenter 
contends that the proposed rule appears to suggest that all systems 
that perform critical functions would be required to withstand the full 
direct strike currents, without taking into account any reduction in 
these currents due to the shielding provided by the airframe.
    As discussed in the NPRM, the purpose of the proposed regulation is 
to require lightning protection for electrical and electronic systems 
that perform critical and essential functions when installed in an 
airplane. Protection may be provided by the airplane structure, 
shielding of the wiring, and enclosures of the individual subsystems. 
The level of protection needed for subsystems is generally specified by 
the airframe manufacturer. In the past, when the airframe manufacturer 
did not specify the level of protection needed, Radio Technical 
Commission for Aeronautics (RTCA) Document DO-160, Section 22, 
``Lightning Induced Transient Susceptibility,'' was used to provide 
guidance. While Section 22 of DO-160 is incomplete, it is currently 
being revised to include the effects of multiple burst and multiple 
stroke test waveforms so as to be in agreement with FAA Advisory 
Circular 20-136, ``Protection of Aircraft Electrical/Electronic Systems 
Against the Indirect Effects of Lightning,'' dated March 5, 1990, and 
Society of Automotive Engineers (SAE Committee Report AE4L-87-3, 
Revision B, dated January 1989. Until the DO-160 revision has been 
completed, the test and analyses described in the advisory circular 
should be used to qualify subsystems. The test waveforms presented in 
Appendix III of the advisory circular represent a severe natural 
lightning environment, including the multiple stroke and multiple burst 
criteria, that is external to the airplane and that may be used by 
certification purposes in accessing the induced effects of lightning. 
The equipment should be protected to the appropriate test level, as 
specified in Appendix IV of the advisory circular, for the proposed 
airplane installations so that the subsystems are able to continue to 
perform their intended functions after the tests are conducted.
    Two commenters suggest that the definitions of the terms 
``critical'' and ``essential'' functions be removed from the proposed 
rule and placed in 14 CFR part 1 of the FAR, Definitions and 
abbreviations.
    The FAA does not concur with this suggestion. The terms 
``critical'' and ``essential,'' as used in the proposed rule, have a 
unique definition based on Secs. 25.1309 (b)(1) and (b)(2) that may be 
inappropriate when used in other rules. Commenters have expressed 
confusion over the use of these terms; therefore, the definitions of 
``critical'' and ``essential'' functions have been integrated into the 
wording of the rule so as not to require separate definitions.
    One commenter suggests that the words ``contribute to or'' be 
removed from the definitions for critical and essential functions given 
in proposed Secs. 25.1315 (c)(1) and (c)(2) because this terminology is 
undefined and can be subject to broad interpretation.
    The FAA does not concur. This terminology is consistent with that 
used in existing regulations and is generally understood by the 
aviation industry. It is used in this rule to convey that although a 
failure by itself may not be catastrophic or major, it may be a 
contributing factor when combinations of failures are considered. For 
example, a latent or undetected failure could contribute to a hazardous 
failure condition when combined with one or more specific failures or 
events. Also, systems that perform only non-essential functions could 
contribute to a failure condition involving an non-essential or 
critical function.
    The same commenter also suggests that the words ``significantly 
impact the safety,'' in proposed Sec. 25.1315(c)(2), be changed to 
``reduce the capability'' for consistency with Sec. 25.1309(b)(2).
    The FAA concurs with this recommendation, and Sec. 25.1315(c)(2), 
now designated as Sec. 25.1315(b), has been revised accordingly.
    Several commenters request clarification as to exactly what is 
meant by the statement that critical functions are ``not affected'' by 
the lightning encounter.
    The FAA concurs that clarification of ``not affected'' is needed; 
therefore, the final rule has been revised to read, ``not adversely 
affected'' in an attempt to convey this intent. Although the words 
``not affected'' were used in the proposed rule, the FAA did not intend 
that the requirement be rigidly applied. The intent of the regulation 
is to require lightning protection for systems that perform critical 
functions to the extent that the critical functions are not adversely 
affected by the lightning event. Determination of when functions are 
adversely affected would be made by the cognizant FAA Aircraft 
Certification Office based on rational engineering judgment on a case-
by-case evaluation of the specified function and the ``effect'' 
presented. Literally applying a standard of ``no effect'' would not be 
reasonable. In determining compliance with special conditions in past 
certification programs, the FAA has accepted upsets of a minor nature 
that do not result in significant fluctuations of control surface 
position or engine thrust. Any effect perceived by the flightcrew would 
need to be evaluated to ensure that it would not lead to a hazardous 
condition. For example, some full authority digital engine control 
(FADEC) systems are designed with two fully redundant channels, either 
of which can control the engine independently. In addition, the logic 
within the FADEC will monitor each channel and, by design, switch 
channels if an anomaly appears on the selected channel. This does not 
necessarily mean that the channel is no longer functional or has 
degraded, because if the backup channel were not functional, the 
selected channel would continue in control. Therefore, it would not be 
considered an adverse effect if a channel transfer in such a system 
occurred in accordance with its accepted design when the airplane is 
exposed to the lightning test waveforms. However, additional tests may 
be required to demonstrate that neither channel would be adversely 
affected when tested individually. For example, a mode change within a 
given channel that could result in the loss of a primary thrust setting 
parameter, resulting in the possibility of a change in thrust level, 
would not be acceptable. Internal monitors that indicate normal 
operation of critical systems must not be damaged by the effects of 
lightning.
    Other examples of adversely affected critical functions are 
hazardously misleading primary flight information, uncommanded flap 
motion and, of course, loss of primary flight controls in a fly-by-wire 
airplane.
    Determination of adverse effects will be handled on a case-by-case 
basis subject to the explanation given above. Perturbations or 
deviations that exceed tolerances agreed upon in the test plan must be 
reported to the FAA for evaluation.
    The same commenters also suggest that adequate lightning protection 
is provided if the airplane is still capable of continued safe flight 
and landing after the lightning encounter.
    The FAA does not agree that the concept of continued safe flight 
and landing is sufficient. The FAA has concluded that a higher level of 
safety is required for systems that perform critical functions when 
exposed to adverse environmental conditions. This concept would be 
violated, for example, if engine failure from an expected environmental 
condition, such as a lightning strike, were allowed because any 
environmental condition that may adversely affect an engine design must 
be assumed to affect all the engines on the airplane. For this reason, 
engines, as installed, must be able to tolerate these conditions 
without damage or serious loss of thrust. This same line of reasoning 
applies to other systems that perform critical functions. Lightning 
strikes to airplanes are unpredictable as to their strength, duration, 
and number. Therefore, continued safe flight and landing of the 
airplane after multiple lightning strikes could not be assured unless 
systems that perform critical functions have a high degree of tolerance 
to the expected lightning strike environment. This basic environmental 
requirement also applies to other environmental conditions, such as 
icing, hail, heavy rain, bird flocks, etc.
    One commenter proposes new wording for Sec. 25.1315(a) that would 
allow crew action to restore critical systems that have been disrupted 
by lightning induced transients.
    The FAA does not concur. Critical function disruption must be 
automatically restored after the lightning encounter. Under certain 
flight conditions, such as during takeoff or landing in instrument 
meteorological conditions when the crew workload is high, the crew may 
not be able to restore the critical function in time to prevent a 
catastrophic even from occurring. The FAA allows crew action to restore 
systems that perform essential functions; however, systems that perform 
critical functions must recover automatically.
    The majority of commenters do not agree that the test waveforms 
should be contained in an appendix to part 25, as proposed in the 
notice. They contend that this information should be presented in an 
advisory circular. Several commenters believe that there will be 
additional adjustments to the description of the lightning environment 
as knowledge of the phenomena increases, and that an advisory circular 
would be easier to revise than an appendix to the FAR. In addition, 
they argue that the FAA should not be legally bound by the criteria in 
an appendix if a change to the description of the environment is 
appropriate.
    The FAA concurs that the proposed appendix should not be adopted. 
As noted by several commenters, the information contained in the 
proposed appendix was taken from SAE Report AE4L-87-3, Revision A, 
entitled ``Protection of Aircraft Electrical/Electronic Systems Against 
the Indirect Effects of Lightning,'' dated October 1988. After the 
notice was published, the AE4L Committee added clarifications of the 
environment definition, including some boundaries on pulse spacing in 
the multiple burst and multiple stroke environments. These have been 
incorporated in Revision B of the SAE document issued in January 1989. 
Because of the potential for further adjustments in the environment 
definition, and because use of the description of the environment set 
forth in the proposed Appendix J is only one means of showing 
compliance with this rule, the FAA concurs that it would be more 
appropriate to present this information in an advisory circular. This 
is also consistent with the FAA's practice of publishing technical 
guidance/procedures for implementing a particular regulation in an 
advisory circular. As noted earlier, the idealized waveforms are 
currently covered in AC 20-136. Accordingly, proposed Appendix J to 
part 25 has been removed from the final rule. However, to provide 
guidelines as to what is involved in showing compliance with the rule, 
general criteria are added to Sec. 25.1315 as paragraph (c). A detailed 
discussion of these criteria is provided in AC 20-136.
    Two commenters consider the definition of the environment given in 
the proposed Appendix to be unrealistic and propose several changes to 
the idealized test waveforms.
    The FAA does not concur that this definition is unrealistic. The 
FAA has worked closely with SAE Committee AE4L in developing the 
idealized test waveforms that are presented in Revision B of Report 
AE4L-87-3. The FAA has adopted these waveforms as acceptable 
representations of a severe natural lightning environment for 
certification purposes and has included them in AC 20-136. The proposed 
changes submitted by the commenters have been forwarded to the AE4L 
Committee for consideration. The FAA will consider appropriate changes 
to the definition of the waveforms in the AC if the Committee 
recommends them.
    Two commenters object to statements in the background and 
discussion of the NPRM that new generation systems and airframes are 
more vulnerable to the indirect effects of lightning than previous 
designs.
    The FAA agrees that new generation systems are not necessarily more 
vulnerable to the indirect effects of lightning if proper design, 
shielding, and grounding techniques are used. However, the use of 
sensitive electronics that respond to low level voltage commands makes 
these systems potentially more vulnerable if they are not properly 
designed and shielded. Reduced electromagnetic shielding provided by 
nonmetallic airframe materials also raises the potential for system 
interference from lightning. The intent of these new lightning 
protection requirements is to maintain the level of safety that is 
inherent in the older airplane designs.
    Two commenters point out that preamble statements are vital to 
defining logical, usable, and economically feasible rules, and suggest 
that specific technologies, system architectures, and function 
susceptibility criteria must be provided instead of generalities if the 
FAA desires to justify the rule on a sound technical basis.
    The FAA does not concur. In order to avoid stifling innovation, the 
FAA specifies the required safety objective in a regulation rather than 
dictating specific design details, whenever possible. In accordance 
with long-standing certification practice, system technologies and 
architectures are proposed by the applicant, allowable function 
susceptibility is determined on a case-by-case basis by the local 
cognizant FAA certification office using published FAA policy and 
engineering judgment.
    One commenter expresses concern that application of the proposed 
rule to existing airplanes could present problems for supplemental type 
certification (STC) applicants when new systems are installed. Many 
airlines, for example, do not have the capability to demonstrate 
compliance.
    The FAA considers lightning to be an environmental condition that 
must be taken into consideration to assure confidence of safe operation 
when a new system is installed in an airplane. Equipment manufacturers 
have historically used the test procedures in RTCA Document DO-160 to 
qualify their equipment to environmental conditions. The capability of 
the equipment to meet the tests described in this document establishes 
a minimum level of protection for system components. Additional 
protection may be provided by the airframe materials, shielding of wire 
bundles, proper equipment grounding, etc. In addition to bench tests, a 
determination should be made that systems that perform critical and 
essential functions, as installed in a given airplane, are provided 
with adequate protection, including margins, and that installation 
level testing and/or verified analysis is adequate. This determination 
is made by the cognizant FAA Aircraft Certification Office, based on 
guidance contained in AC 20-136, and sound engineering judgment. In 
addition, the FAA has issued special conditions for new systems in 
existing airplanes under the provisions of Sec. 21.101(b)(2). The 
extent of review required for a system installed in existing airplanes 
will depend on the type of system, installation considerations such as 
type of airplane, airframe materials (metallic or composite), service 
experience in ``similar'' airplanes, and other factors. These 
evaluations should be reviewed with the cognizant FAA Aircraft 
Certification Office so that the FAA and the applicant can agree on a 
certification plan.
    One commenter states that the proposed requirement for lightning 
protection of essential systems is not justified and should not be 
adopted.
    The FAA disagrees with this comment. Lightning encounters, even 
though infrequent , do occur. Therefore, a degree of protection is 
required commensurate with the criticalness of the function that the 
system performs. Protection requirements are much less stringent for 
systems that perform essential functions than for those that perform 
critical functions. System components may be damaged as long as the 
function can be recovered after the lightning encounter. The 
justification for imposing requirements for systems that perform 
essential functions is that loss of function would unacceptably 
decrease the inherent level of safety of the airplane.
    One commenter questions whether manufacturers would be responsible 
for testing and recertifying critical electronic control systems now in 
service.
    The new lightning protection requirements apply to systems that 
perform critical and essential functions of which design approval is 
sought after the effective date of the rule. Recertificating in-service 
units is not required. If an in-service problem that affects the safety 
of the airplane were discovered, an airworthiness directive would be 
issued requiring corrective action.
    One commenter does not consider that the imposition of additional 
lightning protection requirements on systems of conventional design is 
justified if service history has shown that they are insensitive to 
lightning transients.
    The FAA does not intend to impose additional lightning protections 
requirements on systems using standard designs and installation that 
can be shown to have an inherent history of acceptability. It is FAA 
policy to accept similarity with previously proven installation 
designs, simulated lightning tests, or acceptable analysis. Individual 
designs should be reviewed by the cognizant FAA Aircraft Certification 
Office.
    Several commenters disagree that the incremental cost of 
implementing the new rule will be zero. These comments and the FAA's 
response are addressed in the Regulatory Evaluation discussion that 
follows.
    Notice 89-15 proposed that the lightning protection standard be 
adopted as Sec. 25.1315 of the FAR. The paragraph used for the final 
rule was changed to Sec. 25.1316 so that a future conflict could be 
avoided in the event the FAA determines that JAR 25.1315, ``Negative 
Acceleration,'' should be adopted.

Regulatory Evaluation

    This section summarizes the full regulatory evaluation prepared by 
the FAA that provides detailed estimates of the economic consequences 
of this regulatory action. This summary and the full evaluation 
quantify, to the extent practicable, estimated costs and anticipated 
benefits to the private sector, consumers, and Federal, state, and 
local governments.
    Proposed changes to Federal regulations must undergo several 
economic analyses. First, Executive Order 12866 directs that each 
Federal agency shall propose or adopt a regulation only upon a reasoned 
determination that the benefits of the intended regulation justify its 
costs. Second, the Regulatory Flexibility Act of 1980 requires agencies 
to analyze the economic impact of regulatory changes on small entities. 
Finally, the Office of Management and Budget directs agencies to assess 
the effects of regulatory changes on international trade. In conducting 
these analyses, the FAA has determined that this rule: (1) will 
generate benefits that justify its costs and is not a ``significant 
regulatory action'' as defined in the Executive Order; (2) is not 
significant as defined in Department of Transportation Regulatory 
Policies and Procedures; (3) will not have a significant economic 
impact on a substantial number of small entities; and (4) will not have 
a negative impact on international trade. These analyses, available in 
the docket, are summarized below.

Costs

    The costs of the rule will essentially equal the costs that would 
have been incurred by manufacturers in complying with requirements 
imposed as special conditions in the absence of this rule. The new 
standards will be no more stringent than those imposed through recent 
special conditions, which are consistent with FAA Advisory Circular 20-
136, ``Protection of Aircraft Electrical/Electronic Systems Against the 
Indirect Effects of Lightning,'' dated March 1990, and SAE Committee 
Report AE4L-87-3, Revision B, dated January 1989. Given the novel 
design features of advanced electronic systems and their susceptibility 
to lightning strikes, the FAA would have continued to require adequate 
lightning protection for all new certifications through imposition of 
special conditions; consequently, this rule imposes no new incremental 
costs.
    Notwithstanding this cost perspective, the FAA has evaluated the 
costs of the rule apart from the existence of special conditions, i.e., 
under the assumption that the reference level of costs prior to this 
rule is zero.
    The relative costs of the final rule are summarized below for two 
type-certifications--a representative part 25 large transport category 
airplane (i.e., air carrier), and a representative part 25 small 
transport category airplane (i.e., a business or commuter jet).
    Based on manufacturers' experiences with special condition 
requirements and other relevant data, nonrecurring testing costs for a 
representative large transport category airplane are estimated to total 
$6,300,000, consisting of $2,000,000 for avionics equipment, $200,000 
for engine controls, and $4,100,000 for airframes. Recurring 
modification costs for each airplane produced are estimated to average 
$50,000 for avionics, $35,000 for engine controls, and $12,600 for the 
airframes, totalling $97,600 per airplane. Assuming 50 airplanes are 
produced each year over a 10 year period (1995-2004), recurring 
modification costs total $48,800,000. Thus, the costs to meet the 
lightning protection requirements for certification of a representative 
large transport category airplane total $55.1 million in nondiscounted 
1990 dollars, or $27.7 million when discounted to 1991 present value.
    For a representative small transport category airplane, 
nonrecurring testing costs are estimated to total $980,000, consisting 
of $630,000 for avionics, $150,000 for engine controls, and $200,000 
for airframes. Recurring modification costs for each airplane produced 
are estimated to average $25,000 for avionics, $8,000 for engine 
controls, and $9,000 for airframes. Assuming production of 50 airplanes 
per year for 10 years (1995-2004), recurring modification costs total 
$21.0 million. Thus, the costs to meet the lightning protection 
requirements for certification of a part 25 small transport category 
airplane total approximately $22.0 million in nondiscounted 1990 
dollars, or $10.5 million when discounted to 1991 present value.

Benefits

    The benefits attributable to the rule are the prevented fatalities, 
injuries, and airplane damage that might otherwise be caused by the 
adverse indirect effects of lightning strikes on airplane electronic 
systems. Information from the FAA Accident/Incident Data System 
indicates that, from 1985 through 1990, there were two incidents 
involving part 25 airplanes (both were large transport category 
airplanes) in which the indirect effects of lightning strikes adversely 
affected electronic systems. In each case, the airplane landed safely 
with minimum damage. In one incident, the first officer's flight 
instruments were lost, and in the second a partial electrical failure 
occurred. Neither of the two airplanes affected were certificated 
within the last five years, and therefore few sophisticated electronic 
systems were involved. Lightning protection requirements imposed 
through special conditions (since 1986) have substantially reduced the 
probability that indirect effects of lightning would disrupt electronic 
systems. Consequently, incidents involving more recent certifications 
that include advanced electronic systems have not occurred. Given the 
complexities of the more advanced electronic systems and their 
increased vulnerability to lightning impacts, inadequate protection of 
the systems would result in increased risks of operational failure.
    As the number of flights increases through normal growth in air 
traffic, the overall number of potential lightning strikes increases 
accordingly. Each transport category airplane experiences, on average, 
1.25 lightning strikes during each year of operation. Thus, between 
15,000 and 16,000 lightning strikes could be expected during the 
operating lives of the airplanes produced under one typical part 25 
certification (i.e., 500 airplanes  x  1.25  x  25 years). Since two 
incidents affecting less advanced systems occurred over a recent five 
year period, it is not unreasonable to postulate that at least this 
number could occur during a future five year period. Given the advanced 
systems' lower tolerance thresholds for disruptions and the 
criticalness of their effect on safe flight and operation, events that 
were incidents in the past could be accidents in the future.
    The FAA has estimated the minimum levels of averted losses (in 
terms of avoided fatalities and airplane damage) that would be 
necessary to offset the expected costs of complying with the rule. For 
a representative part 25 large transport category airplane 
certification, the requirements will be cost-beneficial if one averted 
accident prevents 91 fatalities and the destruction of the airplane. 
For a representative part 25 small transport category airplane 
certification, the rule will be cost-beneficial if 2 averted accidents 
prevent 36 fatalities and 2 destroyed airplanes. For the reasons 
outlined above, the FAA expects that the new requirements will prevent 
at least the minimum number of accidents specified and therefore 
considers the rule to be cost beneficial.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily and 
disproportionately burdened by government regulations. The RFA requires 
agencies to review rules that may have ``a significant economic impact 
on a substantial number of small entities.''
    The rule will affect transport category airplane manufacturers. 
None of these manufacturers is considered to be a small entity in 
accordance with FAA criteria which states that a small manufacturer is 
one with 75 employees or less. Therefore, this rule will not have a 
significant economic impact on a substantial number of small entities.

International Trade Impact Assessment

    The rule will have little or no impact on trade for either American 
firms doing business in foreign countries or foreign firms doing 
business in the United States. In the U.S., foreign manufacturers will 
have to meet U.S. requirements, and thus will gain no competitive 
advantage. In foreign countries, American manufacturers need not comply 
with these requirements if the foreign country does not require them 
and, therefore, will not be placed at a competitive disadvantage 
relative to foreign manufacturers.

Federalism Implications

    The regulations adopted herein will not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
regulation does not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.

Conclusion

    For the reasons given above, the FAA has determined that this 
regulation is not significant under Executive Order 12866. In addition, 
the FAA has determined that this action is not significant as defined 
in Department of Transportation Regulatory Policies and Procedures (44 
FR 11034, February 26, 1979). Since the aircraft involved are not 
manufactured by small entities, the FAA certifies, under the criteria 
of the Regulatory Flexibility Act, that this regulation will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities. A copy of the regulatory evaluation prepared 
for this regulation may be examined in the public docket or obtained 
from the person identified under the caption, FOR FURTHER INFORMATION 
CONTACT.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Federal Aviation Administration, 
Reporting and recordkeeping requirements.

The Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration amends 14 CFR part 25 of the Federal Aviation 
Regulations (FAR) as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

    1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 1344, 1354(a), 1355, 1421, 1423, 1425, 
1428, 1429, 1430); 49 U.S.C. 106(g); and 49 CFR 1.47(a).

    2. A new Sec. 25.1316 is added under the undesignated center 
heading ``General'' to read as follows:


Sec. 25.1316  System lightning protection.

    (a) For functions whose failure would contribute to or cause a 
condition that would prevent the continued safe flight and landing of 
the airplane, each electrical and electronic system that performs these 
functions must be designed and installed to ensure that the operation 
and operational capabilities of the systems to perform these functions 
are not adversely affected when the airplane is exposed to lightning.
    (b) For functions whose failure would contribute to or cause a 
condition that would reduce the capability of the airplane or the 
ability of the flightcrew to cope with adverse operating conditions, 
each electrical and electronic system that performs these functions 
must be designed and installed to ensure that these functions can be 
recovered in a timely manner after the airplane is exposed to 
lightning.
    (c) Compliance with the lightning protection criteria prescribed in 
paragraphs (a) and (b) of this section must be shown for exposure to a 
severe lightning environment. The applicant must design for and verify 
that aircraft electrical/electronic systems are protected against the 
effects of lightning by:
    (1) Determining the lightning strike zones for the airplane;
    (2) Establishing the external lightning environment for the zones;
    (3) Establishing the internal environment;
    (4) Identifying all the electrical and electronic systems that are 
subject to the requirements of this section, and their locations on or 
within the airplane;
    (5) Establishing the susceptibility of the systems to the internal 
and external lightning environment;
    (6) Designing protection; and
    (7) Verifying that the protection is adequate.

    Issued in Washington, DC, on April 20, 1994.
David R. Hinson,
Administrator.
[FR Doc. 94-10169 Filed 4-26-94; 8:45 am]
BILLING CODE 4910-13-M