Summary/Background: 

Memorandum

U.S. Department 

of Transportation 

Federal Aviation 

Administration 

Subject:

INFORMATION: SFAR 88 – Mandatory Action 

Decision Criteria 

Date: February 25, 2003 

From: Manager, Transport Standards Directorate, 

Aircraft Certification Service, ANM-100 

Reply to 

Attn. of: 2003-112-15 

To: See Distribution Regulatory

Reference: SFAR 88 

The purpose of this memorandum is to provide standardized policy for determining the 

need for mandatory action relative to the findings from the fuel system safety review 

required by Special Federal Aviation Regulation Number 88 (SFAR 88). SFAR 88 

requires certain Type Certificate (TC) and Supplemental Type Certificate (STC) holders 

to conduct a system safety review of fuel tank systems on transport category airplanes 

using the provisions of 14 CFR 25.981 (a) and (b) (Amendment 25-102) and 25.901 and 

submit a report to the FAA. The compliance dates for TC holders and STC holders are 

December 6, 2002, and June 6, 2003, respectively. These reviews are a “re-evaluation” 

of previously approved fuel systems using the current ignition prevention standards 

(Amendment 25-102). Note that the SFAR 88 process is not a re-certification effort. 

SFAR 88 is a process for determining what design and/or maintenance improvements 

would be required to bring each existing transport category airplane into compliance with 

14 CFR 25.981 (a) and (b) (Amendment 25-102) and 25.901. Some of these 

improvements may warrant airworthiness directives implemented under Part 39, others 

may not. A “Spot Amendment” to SFAR 88, Amendment 21-82, was issued to add an 

equivalent safety finding provisions and clarify that fuel tank systems designs not 

meeting the new standards will be further reviewed under part 39, Airworthiness 

Directives, to determine if design changes or other action are required to resolve unsafe 

conditions. SFAR 88 was also revised to allow additional time for STC holders and 

operators to comply. 

Recently several applicants have requested use of equivalent safety provision of the Spot 

amendment and have proposed use of inerting systems, or polyurethane foam in 

combination with certain design changes and maintenance actions to address ignition 

sources. These proposals have introduced the concept of flammability reduction as a 

factor in determining unsafe conditions on in-service airplanes. In order to determine 

which fuel tank system design feature will require mandatory action, the FAA has 

established a 4-element unsafe condition evaluation criteria that was presented in the 

November 19, 2002, Fuel Tank Safety Workshop held in Washington, D.C. This 

memorandum will expand on the guidance that was presented at that workshop. The 
Federal Aviation Administration (FAA) and Joint Aviation Authorities (JAA) have 

developed this harmonized criteria for determination of an unsafe condition based upon 

the findings from the SFAR 88 fuel tank system safety review. 

One of the elements used in this evaluation criteria involves a determination of whether 

the fuel tank is classified as having a relatively high flammability exposure time, or 

having a relatively low flammability exposure time. Except for the case where an 

ignition source is continuously present, a relatively low fuel vapor flammability exposure 

time substantially decreases the probability of tank explosions (low risk). While a higher 

flammability exposure time has been associated with higher risk, given a similar 

intermittent exposure to ignition sources. In general, unheated aluminum wing tanks and 

unheated center wing tanks fueled with Jet A have exhibited an acceptable level of 

safety. Wing and body tanks fueled with JP-4 (or a mixtures of Jet A and JP-4) and 

heated center wing tanks fueled with Jet A have not had an acceptable level of safety on 

many airplanes. 

The consideration of flammability exposure time in the unsafe condition determination 

process is not intended to imply that ignition source prevention is unimportant for tanks 

with low flammability exposure time. The fundamental method for preventing fuel tank 

explosions involves establishing that the fuel tank system designs do not develop a 

condition that would result in an ignition within the fuel tank ullage space and fluid 

leakage zones (i.e. ignition prevention). Ignition prevention measures will still be the 

principle line of safety in the fuel tank system. However, the unsafe condition 

determination will take into consideration the tank flammability exposure time in 

determining the extent of ignition source reduction needed. 

This memorandum provides guidance to be used for determining unsafe conditions, due 

to ignition sources, based upon results from the one time design reviews conducted to 

evaluate compliance with §§ 25.981 (a) and (b) (Amendment 25-102) and 25.901 in 

accordance with SFAR 88. The TC and STC holder’s system safety assessment provided 

in their fuel tank system design reviews and flammability exposure time determination of 

each fuel tank is the basis for the determination of the unsafe condition. The method to 

determine flammability exposure time of a given fuel tank is provided in Element 4 and 

attachment 2 of this memo. 

Current Regulatory and Advisory Material: 

1. SFAR 88 latest amendment, effective 12/9/02 

2. Sections 25.901, and 25.981 (a) and (b) as amended by Amendment 25-102 

3. AC 25.981-1B or C (draft) 

Definitions: 

The following definitions only apply to this policy memorandum. 

a) Extremely Improbable: An event is considered to be extremely improbable if it is so 

unlikely that it is not anticipated to occur during the entire operational life of all 

airplanes of one type. In quantitative terms, a failure or condition that can be 

anticipated to occur at a rate in the order of 10-9 events per flight hour or less. (Based 

on JAA ACJ 25.1309 & draft FAA AC 25.1309) 

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b) Extremely Remote: An event is considered to be extremely remote if it is unlikely to 

occur during the entire operational life of all airplanes of one type, but nevertheless 

has to be considered as being possible. In quantitative terms, a failure or condition 

that can be anticipated to occur at a rate between 10-7 and 10-9 events per flight hour. 

(Based on JAA ACJ 25.1309 & draft FAA AC 25.1309) 

c) Flammable: Flammable with respect to a fluid or gas, means readily susceptible to 

ignition or to exploding. (14 CFR part 1, Definitions) 

d) Flammability Exposure Time: The percent of operational time that the fuel tank 

ullage is flammable over the expected range of operational conditions during many 

different mission simulations. The simulations use the approved fuel types for the 

airplane model. It is calculated using the FAA Monte-Carlo method. 

e) Flammable fluid leakage zones: Any area where flammable liquids or vapors are not 

intended to be present, but where they might exist due to leakage from flammable 

fluid carrying components (e.g. leakage from tanks, lines). Examples of these areas 

include: 

• The wing leading (including any adjacent compartment such as the 

strut) and trailing edges, 

• Farings located below the fuel tanks, 

• Wheel wells, 

• Fuel pump enclosures, 

• Unpressurized areas of the fuselage surrounding fuel tanks, and

• Areas containing flammable fluid lines or tanks. 

f) Foreseeable: An event or condition is foreseeable if the physics of the failure can be 

defined and the occurrence of the failure during the exposure period in question 

cannot be acceptably ruled out. The level of probability where an event is no longer 

considered “foreseeable” lies somewhere between "extremely improbable" and 

“impossible.” Any event that is “impossible” is clearly not “foreseeable.” All events 

that are not “extremely improbable” are considered “foreseeable.” However, for 

those events whose probability lie between “extremely improbable” and 

“impossible”, the determination as to whether or not they are to be considered 

“foreseeable” has less to do with their "probability" and more to do with the 

confidence we have in the provisions made to actively preclude their occurrence (e.g. 

design margins, quality assurance, conservative maintenance provisions, etc.). The 

bottom line is, if we don't have confidence the event will not occur, then it should be 

considered “foreseeable.” 

g) Hazardous Energy: Energy into the fuel tanks greater than 200 micro-joules and 

surface temperatures in the fuel tank greater than 400 deg F. 

h) Known: Those conditions which have occurred in-service and are likely to occur on 

other products of the same or similar type design, and conditions which have been 

subject to mandatory corrective actions, following in-service findings, on products 

with a similar design of fuel system. 

i) Low and High Flammability Exposure Time: In determining whether a fuel tank is 

classified as either a tank with low or high flammability exposure time for the 

mission profile: 

• Fuel tanks with low flammability exposure time are defined as those 

tanks that have a fleet average flammability exposure time no more 

than 7% using the FAA Monte-Carlo Model method. 

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• Fuel tanks with high flammability exposure time are those tanks that 

have a fleet Average Flammability exposure time of greater than 7% 

using the FAA Monte-Carlo Model method. 

j) Monte-Carlo Method: The Monte-Carlo method was agreed to during both the 1998 

and 2000 ARAC fuel tank harmonization working groups as the preferred method of 

analysis for determining flammability exposure time of a fuel tank. Monte-Carlo 

analysis is a simulation that calculates values for the parameter of interest by 

randomly selecting values for each of the uncertain variables from predetermined 

distribution tables. This calculation is conducted over and over to simulate a process 

where the variables are random within defined distributions. The results of a large 

number of calculations can be used to approximate the results of real world 

conditions. The Monte-Carlo Model should be run for at least 1,000 flights to 

generate a representative average percent flammability exposure time. The FAA 

approved model is available on FAA web site: 

http://qps.airweb.faa.gov/sfar88flamex

k) Unheated Aluminum Wing Tank: A conventional aluminum structure, integral tank of 

a subsonic transport wing, with minimum heat input from aircraft systems or other 

fuel tanks that are heated. 

l) Ullage or Ullage Space: The volume within the tank not occupied by liquid fuel at 

the time interval under evaluation. 

Policy: 

SFAR 88 design reviews relative to the design standards of §§ 25.981 (a) and (b) and 

25.901 may show that some fuel systems or components do not meet these design 

standards using AC 25.981-1 for guidance. The items identified by that review will be 

evaluated using the criteria herein to determine if an airworthiness directive is warranted. 

These criteria require identification of any unsafe conditions that would require 

corrective action regardless of tank flammability exposure time (e.g. single failures such 

as an electrical arc through a conduit). The criteria allow for flammability exposure time 

to be considered when evaluating the need for corrective action for certain combinations 

of failures. The applicant may choose to make a determination of high or low 

flammability exposure time using FAA approved methods, which are discussed in 

Element 4, and if they choose not to make a determination, the FAA will assume high 

flammability exposure time for their tanks. The method described in Element 4 includes 

an initial evaluation of tank cooling characteristics to determine if a tank is considered as 

high or low flammability exposure time. In general unheated wing tanks would be found 

to meet the low flammability exposure time criteria upon inspection. If the initial 

evaluation shows a tank does not meet the low flammability exposure time criteria, a 

further evaluation using the FAA Monte-Carlo analysis is required. 

These criteria do not provide the entire basis for the decision on the actual 

implementation of mandatory corrective action (e.g. compliance time determination) on 

the aircraft type under consideration. Experienced engineering judgment is critical in 

determining assumptions, expected failure rates, and relationships between failures. The 

final decision will be made under the normal processes for issuing ADs (part 39) with the 

addition of a mandatory action advisory board whose function is to ensure 

standardization in the decision making process. A summary of the SFAR 88 AD 

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determination criteria is presented in the attached Table 1, “SFAR 88 Unsafe Condition 

Determination Criteria.” 

Four-Element Unsafe Condition Evaluation Criteria 

Element 1. Single Failures – all tanks

For any tank (with a high or low flammability exposure time), any foreseeable single 

failure condition, regardless of probability and service experience, that may result in a 

potential ignition source within the fuel tank system is considered an unsafe condition 

and must be addressed by corrective action (i.e. AD). 

In general, the FAA does not accept a probabilistic determination that a single failure 

be extremely improbable. However, experienced engineering judgment may enable 

an assessment that such a failure is not foreseeable. The assessment logic and 

rationale should be readily obvious that a knowledgeable, experienced person would 

unequivocally conclude that the failure condition simply would not occur. When 

making such an assessment, all possible and relevant considerations should be taken 

into account, including all relevant attributes of the design. Extensive service 

experience alone showing that the failure condition has not yet occurred is not 

sufficient reason to indicate that a single failure condition cannot exist. 

Element 2. Combination of failures 

a) Fuel tanks with low flammability exposure time 

For fuel tanks with low flammability exposure time, known combinations of 

failures are considered an unsafe condition and must be addressed by corrective 

action (i.e. AD). 

Known combinations of failures includes combinations of failures which have 

occurred in-service and are likely to occur on other products of similar type 

design (i.e. products with a similar design of the fuel system), and combinations 

of failures which have been subject to mandatory corrective actions, following inservice findings, on products with a similar fuel system designs. 

b) Fuel tanks with high flammability exposure time 

For fuel tanks with high flammability exposure time, non-compliant design 

features and associated maintenance actions identified by the system safety 

analysis that was conducted for the one time SFAR 88 design review will be used 

for establishing unsafe condition. These will be considered as unsafe conditions 

(i.e. strict compliance to §§ 25.981 (a) and (b) (Amendment 25-102) and 25.901 

using guidance in AC 25.981-1 must be found) and must be addressed by 

corrective action (i.e. AD). 

Element 3. Unacceptable service experience – all tanks

For any tank (either high or low flammability exposure time), all failures identified in 

service, that result in thermal or electrical energy dissipation into the fuel tank system

which could create an ignition hazard, or making fuel tank safety protection devices 

inoperative (e.g. fuel pump canister, wire sleeving, bonding lead), are considered 

unsafe conditions and must be addressed by corrective action (i.e. AD). Those 

failures may result from equipment or component failures, aging, as well as 

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production or maintenance errors, and inappropriate flight deck actions (such as, 

leaving fuel pumps “ON” beyond their design usage). 

Element 4. Determination of the flammability exposure time of each fuel tank

Typically, aluminum wing tanks without any heating source are considered to have a 

low flammability exposure time. However, several parameters including tank 

volume, geometry, amount of fuel remaining from the previous flight, ambient 

temperature, temperature of loaded fuel, time on the ground, may influence 

flammability exposure time. Determination of flammability exposure time of each 

fuel tank is required. In the absences of any substantiating analysis, all tanks shall be 

considered as a “high flammability exposure time” fuel tank. Table 2, “Flammability 

Exposure Time Determination,” is attached at the end of this memorandum, which 

summarizes the following discussion on determining fuel tank flammability exposure 

time. 

Acceptable method of analysis 

In the absence of another method agreed to by the FAA, the following guidance is 

considered an acceptable means of establishing the flammability exposure time of 

each fuel tank. Other methods may be proposed, but shall be approved by the 

FAA. For the purpose of the assessment of in-service aircraft, this three-step 

approach has been harmonized between FAA and JAA. 

Low Flammability Exposure Time Tank Determination: 

Step 1. 

Does the tank have characteristics of a Low Flammability Exposure Time tank, as 

defined below, by inspection and qualitative design review? 

If Yes, tank is a Low Flammability Exposure Time Tank, if No, go to Step 2 

Step 2.

Can the tank meet the abbreviated quantitative criteria for a Low Flammability 

Exposure Time Tank? 

If Yes, Tank is a Low Flammability Exposure Time Tank, if No, go to Step 3 

Step 3.

Can the tank meet the Low Flammability Exposure Time Tank Criteria using the 

FAA Monte-Carlo analysis and ground fuel temperature limit? 

If Yes, Tank is a Low Flammability Exposure Time Tank, If No, Tank is a High 

Flammability Exposure Time Tank. 

Characteristics of a Low Flammability Exposure Time Tank 

For Step 1: 

The qualitative design review criteria for a low flammability exposure time tank 

are: 

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1. During 4 hour operation on the ground on a 100 deg F day, a fuel temperature 

rise of less than 10 Deg F above ambient with an 80% full fuel load. Heat 

inputs to be addressed are any airplane based heat sources, both internal and 

external to the tank, including heat transfer from an adjacent tank that could 

heat the subject tank. 

And 

2. The ability of the tank to reject heat quickly to outside air. A conventional 

aluminum skin stringer construction, with a high percentage (80 to 90%) of 

the tank surface exposed to free stream air will satisfy this criterion. 

For Step 2: 

The abbreviated quantitative criteria for a low flammability exposure time tank 

are: 

1. During 4 hour operation on the ground on a 100 deg F day, a fuel temperature 

rise of less than 10 Deg F above ambient with an 80% full fuel load. Heat 

inputs to be addressed are any airplane based heat sources, both internal and 

external to the tank, including heat transfer from an adjacent tank that could 

heat the subject tank. 

And 

2. Initial cruise fuel cooling rates of 20 Deg F per hour, with tank 80% Full, and 

35 Deg F per hour with tank empty, starting from a fuel temperature of 60 

Deg F, and TAT of –20 Deg F, 

And 

3. The fuel temperature at the end of a maximum range cruise shall be within 10 

Deg F of TAT.

For Step 3: 

The criteria for a low flammability exposure time tank are: 

1. Has a Fleet Average Flammability exposure time of no more than 7% using 

the FAA Monte-Carlo Model method. 

And 

2. A fuel temperature rise of less than 20 Deg F on the ground starting with a 

100 deg F ambient temperature and minimum operational fuel loaded in the 

tank, considering a ground operation period of at least four hours. Heat inputs 

to be addressed are any airplane based heat sources, both internal and external 

to the tank, including heat transfer from an adjacent tank anticipated to occur 

during the 4 hour period that could heat the subject tank. 

Discussion 

This approach would provide an evaluation of the thermal characteristics of the tank 

in question, and if it met the criteria above, the tank would be considered a low 

flammability exposure time tank. If a tank does not meet the above criteria it will be 

classified as a high flammability exposure time tank for the purpose of making 

unsafe condition findings. The Monte-Carlo model uses a flammability envelope 

that is based on a one joule spark, as being a relatively large spark, and in the lack of 

any real data on the distribution of spark sizes in a fuel tank, a conservative approach 

seemed appropriate. The model is an excel spreadsheet, and is downloadable from

the FAA web site, http://qps.airweb.faa.gov/sfar88flamex . It is required to use 

version 5a or later of the Monte-Carlo model and provide documentation of how the 

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analysis was performed. See attachment 3 for guidance on how the documentation 

should be performed. 

Flammability Reduction or Effects of Ignition Mitigating Devices 

A suitable flammability reduction system such as inerting, or an ignition mitigating 

device such as foam, etc, may be used for ignition source mitigation. High flammability 

exposure time fuel tanks can be treated as low flammability exposure time fuel tanks for 

the purpose of SFAR 88 AD determination, if the mitigation of these devices is found 

acceptable by the Aircraft Certification Office (ACO) or office of the Transport Airplane 

Directorate having cognizance over the type certificate. 

Systems & Areas Adjacent to the Fuel Tank 

In general, the fire protection philosophy for any area considered a flammable fluid 

leakage zone is to assume that flammable vapors may be present in the zone and to 

minimize the probability of ignition of the vapors in accordance with § 25.863(a). This 

has typically been accomplished by using various standards of explosion-proof 

components and good design practices. 

The existence of an unsafe condition should be determined based on the probability of a 

leak (taking into account in-service experience, and mitigating factors such as using 

double walls, protective coating, etc.), and considering the potential ignition sources and 

the design precautions taken in the area (component qualification, drainage, ventilation).

Unsafe conditions must be addressed by corrective action (i.e. AD). 

Maintenance Considerations 

Results of safety assessments may define mandatory maintenance actions needed to 

prevent an unsafe conditions. These maintenance actions must be included in the 

limitation section of the instructions for continued airworthiness. Some manufacturers 

have developed airworthiness limitations (referred to as “Fuel System Limitations” by 

some manufactures) to differentiate these limitations from structural limitations. The 

limitations and critical design configuration control limitations (CDCCL) must be 

addressed in accordance with the standards of § 25.981(b) (Amendment 25-102) to 

ensure fuel tank system protective features are maintained and/or controlled. 

Effect of Policy 

The general policy stated in this document does not constitute a new regulation or create 

a new norm, but is for the purpose of clarifying the considerations for determining an 

unsafe condition using the findings from the one time fuel tank safety review conducted 

for SFAR 88. These criteria are intended to compliment the associated SFAR 88 advisory 

material and help determine which corrective action should or should not be introduced 

on in-service Airplanes. The office that implements policy should follow this policy 

when applicable to the specific SFAR 88 project. Whenever an applicant's proposed 

method of compliance is outside this established policy, it must be coordinated with the 

policy issuing office, e.g., through the issue paper process or equivalent. 

Applicants should expect that the certification officials will consider this information 

when making determination of unsafe conditions for the fuel system design features 

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identified from the system safety analysis conducted for the one time SFAR 88 design 

review. 

If you have further questions, the person on my staff most familiar with this issue is 

Mr. Dennis Kammers (425-227-2956). 

 /s/ Michael J Kaszycki 

for Vi L. Lipski 

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cc: ANM-111, ANM-112, ANM-113, ANM-115, ANM-116, ANM-117 

DISTRIBUTION: 

Manager, Aircraft Engineering Division, AIR-100 

Manager, Seattle Aircraft Certification Office, ANM-100S 

Manager, Boston Aircraft Certification Office, ANE-150 

Manager, New York Aircraft Certification Office, ANE-170 

Manager, Ft. Worth Airplane Certification Office, ASW-150 

Manager, Ft. Worth Special Certification Office, ASW-190 

Manager, Atlanta Aircraft Certification Office, ACE-115A 

Manager, Wichita Aircraft Certification Office, ACE-115W

Manager, Chicago Aircraft Certification Office, ACE-115C 

Manager, Anchorage Airplane Certification Office, ACE-115N 

Manager, Los Angeles Aircraft Certification Office, ANM-100L 

Manager, Denver Airplane Certification Office, ANM-100D 

Manager, Brussels Aircraft Certification Office, AEU-100 

International Field Representative for Transport Directorate, AEU-102 

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TABLE 1 

SFAR 88 Unsafe Condition Determination Criteri

ELEMENT 4: Flammability Exposure Time 

A 

High Flammability Exposure 

Time tanks

B 

High Flammability Exposure Time 

tanks driven to Low Flammability 

Exposure Time tanks through inerting 

or other means 

E

ELEMENT 1: Evaluation for Single Failures 

Unsafe if: Foreseeable Single Failures Jeopardize Safe Operatio

Required Action: All identified single failure conditions must be addressed by corr

ELEMENT 2: Evaluation for Combinations of Failures 

“Compliance” 

Unsafe if: Any noncompliance to 

§§ 25.981 (a) or (b) (Amendment 

25-102) or 25.901 using guidance 

in AC 25.981-1 

Required Action: It is expected 

that any noncompliance finding 

will be considered as an unsafe 

conditions and addressed by 

corrective actions (i.e. AD) 

Unsafe if: Known Combinations of Failure

Operation 

Required Action: All known combinations 

addressed by corrective action (i

ELEMENT 3: Evaluation for In-Service Experience 

Unsafe if: In-service failures exist that either a) dissipate energy into tank/create i

compromise fuel tank safety protection devices 

Required Action: All of the in-service failures must be addressed by correctiv

Attachment 1 
Table 2 

Flammability Exposure Time Determination 

Step 1Can the tank satisfy the Low Flammability exposure time characteristics by qualitative inspection and design review?If Yes, tank is a Low Flammability exposure time tank, if No, go to Step 2 Step 2Can the tank meet the Quantitative criteria for a Low Flammability exposure time tank?If Yes, Tank is a Low Flammability exposure time tank, if No, go to Step 3 Step 3Can the tank meet the Low Flammability exposure time tank Criteria using the FAA Monte-Carlo analysis?If Yes, Tank is a Low Flammability exposure time Tank, If No, Tank is a High Flammability exposure time tank 

Characteristics of a Low Flammability Exposure TLow Heat Input:Step 1: Qualitative Inspection &Design Review: No or very small airplane based heat sources (A fuel temp rise above ambient on the ground, for a 100 deg F day with an 80% internal/external to the tank, including heat transfer from an acould heat the tank, and Ability to reject heat quickly to outside air. A conventional Astringer construction, high percentage (80 to 90%) of surfaces stream air Step 2: Quantitative Determination:Less than 10 Deg F above ambient temperature rise on the growith an 80% full fuel load, and Initial cruise cooling rates of 20 Deg F per hour, with tank 80% per hour with tank empty, starting from 60 Deg F and a TAT oEnd of long cruise tank temperature within 10 Deg F of TAT Step 3: Monte-Carlo Method:Has a Fleet Average Flammability exposure time of no greateFAA Monte-Carlo Model, and A fuel temperature rise of less than 20 deg F on the ground staF day 

Attachment 2
Attachment 3 

Documenting the Results of the Flammability Exposure Time Determination

This attachment provides guidance on how TC and STC holders should assemble 

documentation for flammability exposure time determination analysis, and when these 

results should be submitted. 

Submittal Options

The results may be submitted to the FAA using any of the options shown below: 

Option 1: 

Submit the flammability exposure time determination results in a self contained 

document or report. The report should be submitted under appropriate cover 

letter to the FAA. 

Option 2: 

The results may be included as an added section of, or appendix to a revised copy 

of the document(s) originally submitted for compliance with SFAR 88. This new 

section should be clearly delineated from the other sections of the document. If 

this option is used, none of the original SFAR 88 non-compliance findings may 

be changed based on the fuel tank flammability exposure time. In other words,

the flammability exposure time results may not be used to re-visit the original 

non-compliances and apply a risk/probability analysis to show compliance with 

§ 25.981 (a) and (b) Amendment 25-102. The flammability exposure time results 

may only be used to determine if mandatory action is required for a given noncompliance. The revised report should be submitted under appropriate cover 

letter to the FAA. 

Option 3: 

The TC or STC holder may submit the results in any other reasonable, formally 

documented format. If this is the case, please ask them to contact the FAA and 

explain their proposed method of submittal. 

Option 4: 

The TC or STC holder may choose to not submit the results of a flammability 

exposure time determination analysis. In this case, for the purposes of 

determining mandatory actions, the FAA should assume the fuel tank is a high 

flammability exposure time fuel tank. 

What to Include in the Documentation

The following should be included in the documentation of the flammability exposure 

time determination analysis. 

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1. A brief summary of the fuel tank configuration. This should include both a schematic 

of the fuel tank system, and diagrams and/or photographs showing the fuel tanks 

(external views). If this has already been done as part of the December 6, 2002 

SFAR 88 document submittal, it is acceptable to refer to the appropriate section(s) of 

those documents. 

2. The flammability exposure time determination method/step used, and the results for 

each fuel tank. These should be documented as follows: 

If Step 1 is used: 

What to include in documentation: 

1. A brief description of the fuel tank, including 

• A qualitative description of all airplane heat sources into the tank, and 

heat sinks (areas drawing heat out of the tank). 

• A qualitative description of the fuel tank construction (i.e. aluminum

skin/stringer construction) 

2. For fuel tank stabilization temperatures, please provide the test data, or heat 

transfer analysis methods used to derive these 

• If test data is provided, a simple plot will suffice. There is no need to provide 

tabulated data. Include the source of the data, and brief details regarding the 

test conditions, and the configuration of the airplane (i.e. how closely did the 

test airplane fuel tanks match the production airplane.) 

• If test data is used, but a correction method is applied to emulate a particular 

ambient temperature (in the case of Step 1, 100 degrees F), please clearly 

indicate this. Also provide a detailed description of the method used to 

correct the test data to the equivalent of a 100 degree F ambient day. 

• If heat transfer methods will be used, please provide a suitable description of 

the methods used, including the development of the various inputs such as 

convective coefficients, and assumed heat rejection of any airplane based heat 

sources. 

3. The Flammability Exposure Time Classification Statement: : 

• Example Statement: “Following the FAA-JAA Harmonized Fuel Tank 

Flammability Exposure Time Determination Methodology, (Company Name) 

has determined this fuel tank may be classified as a Low Flammability 

Exposure Time Fuel Tank.” 

4. Any other descriptive material, or data deemed appropriate 

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If Step 2 is used: 

What to include in documentation: 

Same as for Step #1 

If Step 3 is used: 

What to include in documentation 

1. A brief description of the fuel tank, including: 

a. A qualitative description of all airplane heat sources into the tank, and 

heat sinks (areas drawing heat out of the tank). 

b. A qualitative description of the fuel tank construction (i.e. aluminum

skin/stringer construction) 

2. The printed “User Input” page from the Monte-Carlo spreadsheet, showing all 

input, and the analysis results. 

3. For each input into the Monte-Carlo spreadsheet, a description of how that input 

was derived. An “input” is when any of the input fields are changed from their 

default values. 

4. For fuel tank stabilization temperatures and time constants, please provide the test 

data, or heat transfer analysis methods used to derive these. 

• If test data is provided, a simple plot will suffice. There is no need to provide 

tabulated data. Include the source of the data, and brief details regarding the 

test conditions, and the configuration of the airplane (i.e. how closely did the 

test airplane fuel tanks match the production airplane.) The FAA will need to 

assess the integrity of this data, as applied to the development of input for the 

Monte-Carlo model. 

• If heat transfer methods will be used, please provide a suitable description of 

the methods used, including the development of the various inputs such as 

convective coefficients, and assumed heat rejection of any airplane based heat 

sources. 

5. If anything in the Monte-Carlo spreadsheet was altered (other than the input fields 

in the input page), please do the following: 

a) Specify the baseline spreadsheet that was altered 

b) Provide a description of why it was changed, what was changed, and any 

supporting data/analysis used to develop the changes. (i.e. an alteration of 

the typical mission length profiles to closer match a specific model). 

c) Describe any testing/validation of the model after the changes were made 

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d) Please ensure that the file name, and the version description within the 

spreadsheet are changed from the baseline model. Include suitable notes 

and descriptive language in the input page, such that this spreadsheet 

cannot be mistaken for a baseline version. 

e) Finally, please provide an electronic copy of the altered spreadsheet to the 

FAA. 

6. The Flammability Exposure Time Classification Statement, as one of the two: 

• Example Statement: “Following the FAA-JAA Harmonized Fuel Tank 

Flammability Exposure Time Determination Methodology, (Company Name) 

has determined this fuel tank may be classified as a (Low/High) Flammability 

Exposure Time Fuel Tank.” 

7. Any other descriptive material, or data deemed appropriate 

When to Submit The Flammability Exposure Time Determination Analysis

For Type Certificate Holders, the flammability exposure time determination analysis 

should be submitted to the FAA prior to or concurrent with the meeting of the mandatory 

action advisory board. 

For Supplemental Type Certificate Holders whose STC involves auxiliary fuel tanks, the 

flammability exposure time determination analysis should be submitted to the FAA prior 

to or concurrent with the meeting of the mandatory action advisory board.