t 3 w 

U.S. Department 

of Transportation 

Fedemi Aviation 

Administration 

Advisory 

Circular 

Subject: ELECTRICAL FAULT AND FIRE Date: 4/5/91 AC No: 25-16 

PREVENTION AND PROTECTION Initiated by: ANM- 100 Change: 

1 PURPOSE. This advisory circular (AC) provides information on electrically 

caused faults, overheat, smoke, and fire in transport category airplanes. 

Acceptable means are provided to minimize the potential for these conditions 

to occur, and to minimize or contain their effects when they do occur. These 

means are not mandatory. An applicant may elect to use any other means found 

to be acceptable by the Federal Aviation Administration for compliance with 

the Federal Aviation Regulations (FAR). 

2 RELATED FAR SECTIONS. The related sections of the FAR are as follows. 

Where applicable, corresponding sections of Part 4b of the Civil Air 

Regulations (CAR) of 1962 follow each cited Part 25 section of the FAR. 

21.21(b)(l) 25.1309(a)/4b.606(a) 

21.21(b)(2) 25.1309(b) 

25.601/4b.300 25.1309(c)/4b.606(b) 

25.603/4b.301 25.1309(d) 

25.671/4b.320(a) 25.1333/4b.612(f) 

25.695 (Initia1)/4b.320(b) 25.135l(b)(2)/4b.622(b)(2) 

25.672 (Amdt. 25-23 or later amdt.)/4b.320(b) 25.1353 

25.831(c)/4b.371(c) 25.1357(a)/4b.624(a) 

25.853/4b.381 25.1359(d) 

25.863/4b.385 25.1363/4b. 627 

25.901/4b.400 25.1435/4b.654 and 4b.655 

25.903/4b.401 25.1529 

25.1307(c)/4b.602 and 4b.605(e) 25.158l(a)(2)/4b.740(c). 

3 RELATED ADVISORY CIRCULARS. The guidance in this AC supplements the 

following existing guidance on safe electrical design and installation 

practices. 

a. AC 43.13.lA, Change 3, Acceptable Methods, Techniques, and 

Practices, Aircraft Inspection and Repair. 

b. AC 43.13.2A, Change 1, Acceptable Methods, Techniques, and 

Practices, Aircraft Alterations. 

c. AC 25-9, Smoke Detection, Penetration, Evacuation Tests, and Related 

Flight Manual Emergency Procedures. 

d. AC 25-10, Guidance for Installation of Miscellaneous, Non-required 

Electrical Equipment. 
AC 25-16 04/05/91 

4 . DEFINITIONS. 

a. Electrical Component: For the purpose of this AC, an electrical 

component is defined as an electrical power source, or a component receiving 

electricity from any source. Sources of electricity are not limited to power 

sources or distribution buses. They also include signal sources, such as the 

output of an autopilot servo amplifier, or data sources that transfer 

information electrically from one component to another. 

b. Circuit Protective Device (CPD): A device used to protect 

electrical/electronic circuit components from an over-voltage or over-current 

condition, by automatically interrupting the current flow. The most common 

types of CPDs used in aircraft are the circuit breaker and the fuse. 

c. Aromatic Polyimide Insulation: A wire insulating material formed as 

the result of a polycondensation reaction between an aromatic dianhydride and 

an aromatic diamine. 

d. Arc: A phenomenon in which a conductive carbon path is 

formed across an insulating surface. This carbon path provides a short 

circuit path through which current can flow. Normally a result of electrical 

arcing. Also referred to as "Carbon Arc Tracking," 'Wet Arc Tracking," or 

"Dry Arc Tracking." 

e. Insulation Flashover: A result of Arc Tracking, an instantaneous 

burn-through of the insulated wire with the possibility of continuing the burn 

into surrounding wires. This failure mode, which is a result of the high 

temperature degradation of the insulation experienced during arcing, can 

propagate through a complete wire bundle severing the entire grouping. 

5 . WIRING FAULT AND WIRE INSULATION FLAMMABILITY INFORMATION. 

a. Backsround. Amendment 25-32, effective May 1, 1972, added a new 

3 25.1359(d) which applies the flammability requirements of Appendix F of Part 

25 to wire insulation used in aircraft and also revised Appendix F to make the 

burn test requirements more stringent. These requirements are effective on 

airplanes for which application for a type certificate is (or was) made on or 

after May 1, 1972; on the Boeing 747, Douglas DC-lo, and Lockheed L-1011 

airplanes by special conditions; and on certain other airplanes. (Reference 

the Type Certificate Data Sheet of each airplane type for its type 

certification basis.) Before these regulatory actions, there were no wire 

insulation flammability requirements in either Part 25 or Part 4b. Certain 

types of insulation, including polyvinyl chloride (PVC) insulation, do not 

comply with the 5 25.1359(d) flammability requirements. 

requirements are referred -to as "later" airplanes, and a 

referred to as "earlier" airplanes. Similarly, wire hav 

b. Discussion. Airplanes subject to the 5 25.1359(d) flammability 

airplanes are 

lation which 

li other 

ing insu 

2 Par 4 
04/05/91 AC 25-16 

complies with these flammability requirements is referred to as 'later" wire, 

and all other wire is referred to as "earlier" wire. 

c. General Guidance. The guidance in this AC supplements existing 

guidance provided in AC 43.13-1A and AC 43.1302A, and should be applied to new 

airplanes, as well as to modifications of previously-certificated airplanes in 

all locations where electrical systems, components, or wires are affected. It 

may also be useful in developing corrective Airworthiness Directive (AD) 

actions taken in response to hazards discovered in service. It should be 

noted that this guidance is not intended to take the place of instructions or 

precautions provided by wire, wire insulation, or equipment manufacturers. 

Also, if any requirement of Part 25 that is included in the airplane's type 

certification basis supersedes any particular guidance in this AC, compliance 

with that requirement of Part 25 should be ensured. This guidance reflects 

past certification practices and is considered to provide acceptable means of 

compliance with, or equivalent safety to, $5 25.1359(d) and 25.831. 

(1) Earlier wire may be used in all locations in earlier airplanes. 

(2) Earlier wire may be used inside the fuselage of later airplanes 

only if its use does not create any significant potential for hazard. Under 

the equivalent safety provision of 5 21.21(b)(l), the potential for hazard is 

considered insignificant if the guidance provided in any of the following 

three paragraphs is followed: 

(i) Earlier wire may be used inside equipment designed, on an 

overall basis, to be as fire-resistant as practicable if it is either: 

(A) Enclosed in a case made of metal or other material 

that complies with the flammability requirements of Amendment 25-32 that will 

either contain an internal fire so that it cannot propagate to other locations 

or is sufficiently airtight that internal ignition sources cannot cause a 

fire; or 

(B) Located and installed where a fire cannot damage 

safety-related parts, propagate to flammable parts, or cause personal injury. 

Maximum physical or spatial separation is especially important above the 

equipment or downstream of any consistent, known airflow. 

(ii) Earlier wire may be used inside the cases of video or 

audio tape players, television receivers, telephones, or other passenger 

convenience or entertainment equipment purchased on the general commercial 

market where similar, economically-feasible equipment having wire which 

complies with 5 25.1359(d) does not exist. In such instances, the equipment 

should be located where smoke or fire would readily be noticed, and a readily 

identifiable switch, located away from the equipment, should be provided to 

enable its safe and rapid disconnection. 

Par 5 
AC 25- I.6 04/05/91 

(iii) Where reasonable and appropriate, very small amounts of 

earlier, special-purpose wire, such as telephone interconnection wires, may 

also be used outside equipment cases. 

d. General Wire Installation Guidance. 

(1) All instructions and precautions provided by wire and wire 

insulation manufacturers should be followed and observed. 

(2) Machines used to stamp identification on wire insulation should 

be adjusted so as not to penetrate through the insulation. Quality assurance 

procedures to verify that penetration has not occurred should be established. 

An acceptable method would be to employ an approved high voltage test. 

Alternatively, a non-impact process to place identification on wire insulation 

may be used. 

(3) Care should be taken to ensure that the clamps and ties around 

wire bundles do not present a rough surface that may damage the wire 

insulation. These clamps and ties should be tight enough to hold the wires in 

place, but not so tight that insulation damage would occur during fabrication 

or installation, or later in service. To prevent insulation chafing, wires 

and bundles should be installed by routing and clamping to ensure sufficient 

spacing from structure or other parts after any single failure. 

Alternatively, other means may be used to prevent insulation chafing after any 

single failure. Some examples of such single failures would include the 

failure of any single clamp or clamp fastener. To prevent insulation damage 

during installation or maintenance, avoid routing wires or bundles in the 

vicinity of parts having sharp edges, corners, or protrusions. Alternatively, 

sharp edges, corners, or protrusions should be covered with smooth protective 

material or other devices. Bend radii should be large enough to ensure that 

insulation cracking does not occur during the fabrication or installation of 

wires or bundles, or later in service due to excessive mechanical stress. The 

clamps should be oriented such that abrasion of the wire or the clamp 

insulation does not occur. The clamps should be a compression type and should 

be spaced so that, assuming a wire break, the broken wire will not contact 

hydraulic lines, oxygen lines, pneumatic lines, or other equipment whose 

subsequent failure caused by arcing could cause further damage. Quality 

assurance procedures should be established to verify that insulation damage 

has not occurred during the process of fabricating and installing wires and 

bundles. 

(4) Abrasion of wire insulation caused by differences in hardness 

can be hazardous. Therefore, wires having significantly different insulation 

hardness, or abrasion characteristics, should be routed in separate bundles. 

This is particularly important in areas of high vibration. Abrasion of either 

the insulation or the insulation-facing material of the clamps, conduits, or 

other devices used to secure or support wires or bundles can also be 

hazardous. Therefore, wire and bundle installations should be designed so 

that the insulation-facing material has a hardness compatible with that of the 

4 Par 5 
04/05/91 AC 25-16 

insulation. Compatible materials are often known by the wire or wire 

insulation manufacturer or the airplane manufacturer or modifier. Compatible 

materials may also have been established by prior satisfactory service 

experience or tests. However, if such information is unavailable, insulation 

and insulation-facing materials should be tested to ensure that differences in 

hardness would not result in abrasion i-n service. 

(5) To prevent insulation damage, wires or wire bundles should not 

be routed in locations where liquid spillage or leakage may be anticipated in 

service. It should be assumed that water or other liquids from any source are 

electrolytic. This assumption applies whether the liquids are pure or have 

other chemical(s) dissolved in or mixed with them. Service experience shows 

that locating wires or bundles under lavatories and galleys has sometimes 

resulted in insulation damage. Locating them in the wheel wells and some 

areas of the wings has also resulted in damage. Locating them in some areas 

of the empennage could also result in damage. Care should be taken to ensure 

that condensation, rain, snow, hail, ice, or slush will not result in 

insulation damage or deterioration of wires or bundles exposed to these 

environments. This may be established by satisfactory service experience, 

tests, or comparison of the insulation chemistry and design with those of 

other types of insulation that are known to be safe when exposed to these 

environments. In particular, the use of aromatic polyimide insulation 

material in these areas should be carefully evaluated. 

(6) Installations that are inherently difficult sometimes lead to 

post-maintenance reinstallations that do not conform to any approved type 

design. Service experience shows that such non-conforming reinstallations, 

especially if done hurriedly, can significantly increase the potential for 

electrical faults, smoke, or fires. Therefore, to the greatest practicable 

extent, a type design should be provided for wire and wire bundle 

installations that allows for easy reinstallation after the completion of 

maintenance. 

(7) Wires and wire bundles should be routed or otherwise protected 

to minimize the potential for maintenance personnel to step, walk, or climb on 

them, or use them for handholds. The wire bundles should be routed along 

heavier structural members whenever possible. Sharp metal edges must be 

protected by grommets to prevent chafing. Wires should not be routed between 

aircraft skin and fuel lines. Avoid running wires along the bottom of the 

fuselage, over the landing gear, in areas of the leading edge of the wing 

where fuel spillage is anticipated, or adjacent to flammable fluid lines or 

tanks. 

(8) In installations where wires or wire bundles are expected to 

flex, such as landing gear harnesses, aromatic polyimide insulated wires 

should be avoided. If this wire type is used in flexible conduit, then the 

conduit installation should be properly designed for this purpose. 

Par 5 
AC 25-16 04/05/91 

6 . CIRCUIT PROTECTIVE DEVICE (CPD) INFORMATION. 

a. Background. Historically, the FAA criterion for circuit protective 

device (e.g., circrit breaker or fuse) selection can simply be expressed as, 

"to protect the aircraft wiring, but not the equipment." This limited 

criterion is based on designing electrical components to be as fire-resistant 

as practicable and either enclosing them in metal cases that will contain an 

internal fire or are sufficiently airtight that internal ignition sources 

cannot cause a fire, or isolating them from flammable materials and 

safety-related parts. In the vast majority of instances metal cases have been 

used. The few exceptions which are known to have resulted' in or contributed 

to fires have been corrected by airworthiness directive (AD) action. However, 

protecting electrical system installations by using CPDs to protect wiring and 

through component design to protect the rest of the system is not adequate. 

Circuit protective devices (circuit breakers and fuses) are considered to be 

slow-acting devices and may not offer sufficient disconnect protection from 

events such as arc-tracking or insulation flashover. For example, service 

experience shows that: 

(1) Selection of CPD ratings; protection of three-phase loads; 

design of connectors, wire bundles, routing and clamping; and component 

temperatures have not always been safe. 

(2) Faulty maintenance sometimes occurs in regard to routing, 

clamping, and cleanliness of locations surrounding certain equipment. 

(3) Aging, weathering, vibration, and the normal wear and tear of 

maintenance sometimes cause chafing, abrasion, or deterioration of insulation, 

which can result in cracks or cuts that expose the conductor. 

(4) The effects of electrical faults can include component 

overheating; toxic fumes; smoke; fire; damage to wires, wire bundles, or 

parts; melting of holes in sheet metal parts by faulted, high-current feeder 

cables; melting and burning of titanium bleed air ducts by a chafed, highcurrent feeder cable; electromagnetic interference (EMI) with equipment; and 

the simultaneous and unrestorable loss of both engine-driven generators in a 

two-engine airplane. While these effects occur infrequently, guidance is 

considered necessary to minimize them when they do occur and to minimize their 

potential causes. These effects can be caused by the following conditions or 

failure modes for which CPD's often do not provide timely, if any, automatic 

protection: 

(i) Intermittent, low impedance short-circuits, such as chafing 

or arcing of wires on grounded metal parts, or chafing between conductors of 

different phases. 

(ii) Higher impedance short-circuits which, for example, can be 

caused by locating wire in a moist or wet environment if the wire insulation 

is cracked or cut. 

Par 6 
04/05/91 AC 250 16 

(iii) Low or higher impedance short-circuits inside electrical 

components themselves; or in component power, signal, or data transfer 

interconnection wires. 

(iv) Failure of power to one or two phases of components 

intended for three-phase power. 

(v) Incorrect assumptions of worst-case load conditions in 

regard to safe component temperatures. 

(vi) Inadequate design 

bundle temperatures. 

(vii) High-current cab 

(viii) Arcing on wire 

damage. Service experience documents 

in regard to safe connector' or wire 

e faults. 

nsulation, or the resulting insulation 

only a relatively small number of 

incidents of arcing damage for all types of insulation. However, service 

experience of aromatic polyimide insulation, as presently constructed, 

documents a failure mode called "insulation flashover" where conduction at 

insulation breakdown areas has damaged or destroyed the wire or wire bundle in 

which it occurs. Also, other adverse effects have sometimes occurred as a 

result of this failure mode. Arcing on wire insulation, or "arc tracking," 

can result from electrolytic contamination of wire having insulation cracks or 

cuts that expose the conductor. It can also result from chafing damage that 

reduces the dielectric strength of dry insulation. Each successive attempt to 

restore an automatically-disconnected power source, or the resetting of an 

automatically-disconnected CPD, can result in progressively worse effects from 

"arc tracking." 

b. Circuit Protective Device Selection And Related Guidance. 

(1) Linear corrections should be made of any measured temperatures 

to the maximum sea level outside ambient temperature approved for operations 

in the Limitations Section of the FAA-approved airplane flight manual (AFM) or 

AFM revision or supplement. Alternatively, they may be corrected in 

accordance with an analysis that establishes a rational method of correction. 

(2) Quality assurance (QA) procedures should be established to 

ensure that circuit breaker time-versus-c 

conform to their specifications, whenever 

Such procedures should be followed before 

rrent automatic trip characteristics 

a specific type or iot is suspect. 

installing circuit breakers. 

(3) To protect against unsafe w 

should be given to the wire size and spec 

deliverable continuous current of the CPD 

i 

i 

l 

re temperatures, consideration 

fication used at the maximum 

disconnection specification for each CPD shou 

into account its ambient temperature and that 

he time-versus-current automatic 

Id also be considered, taking 

of the protected wire. If doubt 

Par 6 7 
AC 25-16 04/05/91 

exists regarding safe wire insulation temperatures, measurements should be 

taken and corrected as described in paragraph 6b(l). 

(4) To minimize deliverable power to potential fault loads, the 

minimum commercially-available CPD rating should be used. This is the rating 

that will power the normal (intended) load without spurious automatic 

disconnections due to temporary conditions such as transients, surges, or 

momentary overloads, 

NOTE: It is recommended that thermal circuit breakers not be 

specified for a continuous load in excess of 85 percent of the 

circuit breaker rating because it may cause deterioration of the 

trip point. 

(5) To protect against propagation of an internal electrical 

component fire to surrounding locations, electrical components should be 

designed using non-flammable or self-extinguishing materials to minimize the 

potential for fire. Electrical components should be enclosed in metal or 

other fire-resistant cases (reference paragraph 5c(2)(i)(A)) that will either 

contain an internal fire or are sufficiently airtight that internal ignition 

sources cannot cause a fire. However, if such a case is impracticable, the 

component should be located and installed where a fire cannot damage 

safety-related parts, propagate to flammable parts, or cause personal injury 

(reference paragraph 5c(2)(i)(B)). Maximum physical or spatial separation is 

especially important above the component, or downstream of any consistent, 

known airflow. 

(6) Precautions should be taken to ensure that three-phase loads are 

not a smoke or fire hazard and do not result in unsafe component temperatures 

when powered by fewer than three phases. Note that three-phase, integral 

(ganged) circuit breakers seldom detect the loss of phases when an overcurrent condition does not exist. If component overheating could occur, 

separate thermal protection should be provided in the equipment case. This 

could occur, for example, as a result of a bus phase outage, a load control 

component failure, or an open wire. If doubt exists regarding safe component 

temperatures, measurements should be taken and corrected as described in 

paragraph 6b( 1). The recommended maximum safe external temperatures are 

considered to be: 450°F for components in dry, clean, and isolated locations; 

400°F for components located in the vicinity of safety-related or flammable 

parts (including liquids or gases), or where flammable waste or other foreign 

material (such as used paper towels) might inadvertently accumulate without 

readily being noticed; and 140°F for components in occupied locations. 

(7) Some internally-faulted components may not cause automatic 

disconnection of their CPD's before causing excessive temperatures that would 

result in a serious personnel, smoke, toxic fumes, or fire hazard. Some 

examples would include certain transformers and motors. In such cases, 

adequate backup protection should be provided. If over-temperature protection 

systems are used, the disconnection of the components protected by these 

8 Par 6 
04/05/91 AC 25-16 

systems should be considered when determining compliance with the applicable 

regulations. This is especially important for components in more than one 

channel of a redundant system, or components in various systems that perform 

operationally-similar functions. Consideration should also be given to 

foreseeable operational and local environmental conditions, and the failure of 

any necessary cooling air supply. 

(8) Protection should be provided against unsafe temperatures in 

connectors and wire bundles. Consideration should be given to probable 

combinations and durations of the maximum normal (intended) loads, combined 

with the simultaneous maximum single continuous fault load for that individual 

wire which would cause the maximum increase in connector or bundle temperature 

(reference paragraph 6b(3)). The maximum safe temperature should be 

determined from the specifications of the connector or the wires with the 

lowest temperature rating. The maximum safe temperature should not be 

exceeded, except in unavoidable applications with high ambient temperatures 

(e.g., the powerplant). If doubt exists regarding safe connector or bundle 

temperatures, measurements should be taken and corrected as described in 

paragraph 6b( 1). 

7 0 MISCELLANEOUS DESIGN, OPERATIONAL. AND MAINTENANCE-RELATED GUIDANCE. 

a. Care should be taken to ensure that EM1 caused by intermittent 

faults does not adversely affect systems or equipment. Such intermittent 

faults can be caused, for example, by chafing of conductors on grounded metal 

parts, chafing between conductors of different phases, or arcing on wire 

insulation. Digital equipment, including digital computer-based equipment, is 

usually more susceptible to such EM1 than other equipment. 

b. It is accepted practice to demonstrate by tests that the generator 

protection system responds properly to faults in the electrical generation and 

distribution system, or in any utilization system. Demonstrations of arcing 

on wire insulation should be allowed to progress to the point of "insulation 

flashover." The tests may be supported by any relevant analysis. If 

laboratory tests are conducted instead of airplane tests, compliance should be 

shown with 5 25.1363. 

c. Penetration of the effects of electrical faults or failure modes 

into tanks, tubes, or components containing fuel, other flammable fluid, 

oxygen, or concentrated oxidizing or reducing agents (such as chemical oxygen 

generators) can be extremely hazardous. Therefore, it is important to ensure 

that any foreseeable penetration will not occur. Some examples of foreseeable 

faults or failure modes that could result in penetration would include 

short-circuits of conductors, arcing on wires or wire bundles, or "insulation 

flashover." Consideration should be given to the maximum power which could be 

produced by such faults or failure modes, and the physical or spatial 

separation provided between their possible locations and the areas of 

potential hazard, Additionally, physical or spatial separation should be 

provided between high-current cables and the areas of potential hazard. 

However, if adequate separation is impracticable, protection should be 

Par 6 
AC 25-16 04/05/91 

provided against the effects of foreseeable faults or failure modes by 

providing alternative physical protection such as an adequate barrier or 

conduit, or by other acceptable means. For example, adequate separation is 

impracticable for wires or bundles that are necessarily located inside of or 

close to fuel tanks, and may be impracticable for some wires or bundles 

located in nacelles or pylons. Whenever practical, aromatic polyimide 

insulation wires should not be used for high current carrying cables. 

d. Electrical components should be assessed for potential fire or smoke 

(which includes harmful or hazardous concentrations of gasses or vapors) 

assuming a failure has occurred. Typically, circuit protective devices and 

metal enclosures are all that are used to control the failure conditions, but 

not in every case (example - overheat protective devices). Each installation 

must be evaluated on its own merits. Electrical equipment bays should contain 

smoke and overheat detectors, and methods should be devised to contain a fire 

and prevent smoke from penetrating into the cabin or the cockpit. Smoke 

detection tests, smoke penetration tests, and smoke evacuation tests should be 

conducted in flight to demonstrate that the methods to detect, control, and 

evacuate the smoke are functioning as designed. The tests should be conducted 

in accordance with the test procedures outlined in AC 25-9. 

e. Electrical components located in fuel vapor zones should be 

qualified as explosion proof in accordance with Section 9 of RTCA Document DO160B, "Environmental Conditions and Test Procedures for Airborne Equipment," 

dated July 20, 1984, or later approved revision. Fuel vapor zones are defined 

by the airplane manufacturer. 

f. Burning of a metal part can be extremely hazardous; therefore, it is 

important to ensure that any foreseeable burning will not occur. Some parts 

made of certain metals, such as magnesium or titanium, can sometimes ignite 

and burn before they melt and drip away. Ignition can be caused by electrical 

faults or failure modes. Whether such a part will burn before it melts 

depends on various factors. Some examples of such factors would include mass; 

electrical and thermal conductivity; design, construction, and installation; 

rate of heat dissipation into surrounding locations; smaller dimensions (e.g., 

metal thickness); presence of sharp or thin edges, corners, or protrusions 

(e.g., cooling fins); air temperature; airflow; and oxygen content. If the 

use of such a part otherwise complies with @ 25.601 and 25.603, consideration 

should be given to the maximum power which could be produced by foreseeable 

faults or failure modes and the physical or spatial separation provided 

between their possible locations and the part. Some examples of such faults 

or failure modes would include short-circuits of conductors, arcing on wires 

or wire bundles, or "insulation flashover." Routing high-current cables in 

the vicinity of such parts should be avoided; however, if adequate separation 

is impracticable, protection should be provided against the effects of 

foreseeable faults or failure modes by the use of alternative physical 

protection, such as an adequate barrier or conduit, or by other acceptable 

means. For example, adequate separation may be impracticable for some wires 

or bundles located in nacelles or pylons. 

10 Par 7 
04/05/91 AC 250 16 

g Information should be provided in FAA-approved AFM's or AFM 

revisions or supplements that the crew should make onlv one attempt to restore 

an automatically-disconnected power source or reset or replace an 

automatically-disconnected CPD that affects flight operations or safety. 

h. Some electrical faults or failure modes can result in the automatic 

disconnection of a power source, bus, or high-current load for which power 

cannot be restored (or will not remain restored) without maintenance action. 

Such a disconnection could result in a serious latent failure of a flight 

control system component if the fault or failure mode occurs in its vicinity. 

For this reason, it is important that maintenance personnel determine by close 

inspection of related and non-related components in the vicinity of the fault, 

and before the next flight, that such a latent failure has not occurred. 

Therefore, this maintenance information should be provided to owners and 

operators of the airplane early enough for well-planned, timely incorporation 

into FAA-approved maintenance programs. 

* &IyJyg<2$ 

Manager; Transport Airplane Directorate 

Aircraft Certification Service, ANM-100 

W.S. Government Printing office: 1991 - 522-242/40101 

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