Summary/Background: 

# Memorandum

U.S. Department of Transportation

Federal Av iation 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 m e m o randum is to provide standardized policy for determ ining the
need for m a ndatory action relative to the findings from the fuel system safety review required by Special Federal Aviation Regul ation Num b er 88 (SFAR 88). SFAR 88 requires certain Type Certificate (TC) and Supplem ental Type Certificate (STC) holders to conduct a system safety review of fuel tank system s on transport category airplanes using the provisions of 14 CFR 25.981 (a) and (b) (Am e ndm ent 25-102) and 25.901 and
subm it a report to the FAA. The com p liance dates for TC holders and STC holders are

Decem ber 6, 2002, and June 6, 2003, respectively. These reviews are a “re-evaluation” of previously approved fuel system s usi ng the current ignition prevention standards (Am e ndm ent 25-102). Note that the SFAR 88 process is not a re-certification effort.

SFAR 88 is a process for determ ining what design and/or m a intenance im provem e nts would be required to bring each existing transport category airplane into com p liance with 14 CFR 25.981 (a) and (b) (Am e ndm ent 25-102) and 25.901. Som e of these
im provem e nts m a y warrant airworthiness directives im plem ented under Part 39, others

m a y not. A “Spot Am endm ent” to SFAR 88, Am endm ent 21-82, was issued to add an equivalent safety finding provisions and cl arify that fuel tank system s designs not

m eeting the new standards will be further reviewed under part 39, Airworthiness Directives, to determ ine if design changes or other action are required to resolve unsafe
conditions. SFAR 88 was also revised to allow additional tim e for STC holders and
operators to com p ly.

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

am endm ent and have proposed use of inerting system s, or polyurethane foam in

com b ination with certain design changes and m a intenance actions to address ignition sources. These proposals have introduced the concept of flam m a bility reduction as a
factor in determ ining unsafe conditions on in-service airplanes. In order to determ ine which fuel tank system design feature will require m a ndatory action, the FAA has
established a 4-elem ent unsafe condition evaluation criteria that was presented in the

Novem b er 19, 2002, Fuel Tank Safety W o rkshop held in W a shington, D.C. This

m e m o randum will expand on the guidance that was presented at that workshop. TheFederal Aviation Adm i nistration (FAA) and Joint Aviation Authorities (JAA) have developed this harm onized criteria for determ ination of an unsafe condition based upon the findings from the SFAR 88 fuel tank system safety review.

One of the elem ents used in this evaluation criteria involves a determ ination of whether the fuel tank is classified as having a relatively high flam m a bility exposure tim e, or having a relatively low flam m a bility exposure tim e. Except for the case where an ignition source is continuously present, a relatively low fuel vapor flam m a bility exposure
tim e substantially decreases the probability of tank explosions (low risk). W h ile a higher
flam m a bility exposure tim e has been associated with higher risk, given a sim ilar
interm ittent exposure to ignition sources. In general, unheated alum inum wing tanks and unheated center wing tanks fueled with Jet A have exhibited an acceptable level of safety. W i ng and body tanks fueled with JP-4 (or a m i xtures of Jet A and JP-4) and
h e a t e d c e n t e r w i n g t a n k s f u e l e d w i t h J e t A h a v e n o t had an acceptable level of safety on

m a ny airplanes.

The consideration of flam m a bility exposure tim e in the unsafe condition determ ination process is not intended to im ply that ignition source prevention is unim portant for tanks
with low flam m a bility exposure tim e. The fundam e ntal m e thod 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 m easures will still be the principle line of safety in the fuel tank system . However, the unsafe condition
determ ination will take into consideration the tank flam m a bility exposure tim e in
determ ining the extent of ignition source reduction needed.

This m e m o randum provides guidance to be used for determ ining unsafe conditions, due to ignition sources, based upon results from the one tim e design reviews conducted to
evaluate com p liance with §§ 25.981 (a) and (b) (Am e ndm ent 25-102) and 25.901 in accordance with SFAR 88. The TC and STC holder’s system safety assessm ent provided in their fuel tank system design reviews and flam m a bility exposure tim e determ ination of
each fuel tank is the basis for the determ ination of the unsafe condition. The m e thod to
determ ine flam m a bility exposure tim e of a given fuel tank is provided in Elem ent 4 and
attachm e nt 2 of this m e m o.

Current Regulatory and Advisory Material:
1. SFAR 88 latest am endm ent, effective 12/9/02
2. Sections 25.901, and 25.981 (a) and (b) as am ended by Am endm ent 25-102
3. AC 25.981-1B or C (draft)

Definitions: The following definitions only apply to this policy m e m o randum

.

a) Extremely Improbable : An event is considered to be extrem ely im probable if it is so unlikely that it is not anticipated to occur during the entire operational lif e of all airplanes of one type. In quantitative term s, 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)

2 of 16b) Extremely Remote : An event is considered to be extrem ely rem o te 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 term s, 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 : Flam m a ble with respect to a fluid or gas, m eans readily susceptible to ignition or to exploding. (14 CFR part 1, Definitions) d) Flammability Exposure Time : The percent of operational tim e that the f u el tank ullage is flam m a ble over the expected range of operational conditions during m a ny different m i ssion sim u lations. The sim u lations use the approved fuel types for the airplane m odel. It is calculated using the FAA Monte-Carlo m e thod. e) Flammable fluid leakage zones: Any area where flam m a ble liquids or vapors are not intended to be present, but where they m i ght exist due to leakage from flam m a ble fluid carrying com ponents (e.g. leakage from tanks, lines). Exam ples of these areas
include:

• The wing leading (including any adjacent com p artm ent such as the strut) and trailing edges,

• Farings located below the fuel tanks,

• W h eel wells,

• Fuel pum p enclosures,

• Unpressurized areas of the fuselage surrounding fuel tanks, and

• Areas containing flam m a ble 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 som e where between "extrem e ly im probable" and
“im possible.” Any event that is “im possible” is clearly not “foreseeable.” All events
that are not “extrem ely im probable” are considered “foreseeable.” However, for those events whose probability lie between “extrem ely im probable” and
“im possible”, the determ ination as to whether or not they are to be considered “foreseeable” has less to do with their "probability" and m o re to do with the confidence we have in the provisions m a de to actively preclude their occurrence (e.g. design m a rgins, quality assurance, conservative m a intenance 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 m i cro-joules and
surface tem p eratures 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 sam e or sim ilar type design, and conditions which have been subject to m a ndatory corrective actions, following in-service findings, on products
with a sim ilar design of fuel system

. i) Low and High Flammability Exposure Time: In determ ining whether a fuel tank is classified as either a tank with low or high flam m a bility exposure tim e for the

m i ssion profile:

• Fuel tanks with low flam m a bility exposure tim e are defined as those tanks that have a fleet average flam m a bility exposure tim e no m o re than 7% using the FAA Monte-Carlo Model m e thod.

3 of 16• Fuel tanks with high flam m a bility exposure tim e are those tanks that have a fleet Average Flam m a bility exposure tim e of greater than 7% using the FAA Monte-Carlo Model m e thod. j) Monte-Carlo Method : The Monte-Carlo m e thod was agreed to during both the 1998
and 2000 ARAC fuel tank harm onization working groups as the preferred m e thod of analysis for determ ining flam m a bility exposure tim e of a fuel tank. Monte-Carlo analysis is a sim u lation that calculates values f o r the param e ter of interest by
random ly selecting values for each of the uncertain variables from predeterm i ned
distribution tables. This calculation is conducted over and over to sim u late a process
where the variables are random within defined distributions. The results of a large

num ber of calculations can be used to approxim a te 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 flam m a bility exposure tim e

. The FAA approved m odel is available on FAA web site: http://qps.airweb.faa.gov/sfar88flam e x k) Unheated Aluminum Wing Tank : A conventional alum inum structure, integral tank of a subsonic transport wing, with m i nim u m heat input from aircraft system s or other
fuel tanks that are heated. l) Ullage or Ullage Space: The volum e within the tank not occupied by liquid fuel at
the tim e interval under evaluation.

Policy: SFAR 88 design reviews relative to the design standards of §§ 25.981 (a) and (b) and
25.901 m a y show that som e fuel system s or com ponents do not m eet these design standards using AC 25.981-1 for guidance. The item s identified by that review will be evaluated using the criteria herein to determ ine if an airworthiness directive is warranted. These criteria require identification of any unsafe conditions that would require corrective action regardless of tank flam m a bility exposure tim e (e.g. single failures such as an electrical arc through a conduit). The criteria allow for flam m a bility exposure tim e to be considered when evaluating the need for corrective action for certain com b inations of failures. The applicant m a y choose to m a ke a determ ination of high or low
flam m a bility exposure tim e using FAA approved m e thods, which are discussed in
Elem ent 4, and if they choose not to m a ke a determ ination, the FAA will assum e high
flam m a bility exposure tim e for their tanks. The m e thod described in Elem ent 4 includes
an initial evaluation of tank cooling characteristics to determ ine if a tank is considered as high or low flam m a bility exposure tim e. In general unheated wing tanks would be found

to m eet the low flam m a bility exposure tim e criteria upon inspection. If the initial
evaluation shows a tank does not m eet the low flam m a bility exposure tim e 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
im plem entation of m a ndatory corrective action (e.g. com p liance tim e determ ination) on the aircraft type under consideration. Experienced engineering judgm ent is critical in
determ ining assum p tions, expected failure rates, and relationships between failures. The
final decision will be m a de under the norm a l processes for issuing ADs (part 39) with the
addition of a m a ndatory action advisory board whose function is to ensure
standardization in the decision m a king process. A sum m a ry of the SFAR 88 AD

4 of 16determ ination criteria is presented in the attached Table 1, “SFAR 88 Unsafe Condition

Determ ination Criteria.”

Four-Element Unsafe Condition Evaluation Criteria
Elem ent 1. Single Failures – all tanks For any tank (with a high or low flam m a bility exposure tim e), any foreseeable single failure condition, regardless of probability and service experience, that m a y result in a potential ignition source within the fuel tank system is considered an unsafe condition
and m u st be addressed by corrective action (i.e. AD).

In general, the FAA does not accept a probabilistic determ ination that a single failure
be extrem ely im probable. However, experienced engineering judgm ent m a y enable

an assessm ent that such a failure is not foreseeable. The assessm ent logic and rationale should be readily obvious that a knowledgeable, experienced person would unequivocally conclude that the failure condition sim p ly would not occur. W h en

m a king such an assessm ent, 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.

Elem ent 2. Com b ination of failures a) Fuel tanks with low flam m a bility exposure tim e For fuel tanks with low flam m a bility exposure tim e, known com b inations of
failures are considered an unsafe condition and m u st be addressed by corrective action (i.e. AD).

Known com b inations of failures includes com b inations of failures which have occurred in-service and are likely to occur on other products of sim ilar type design (i.e. products with a sim ilar design of the fuel system ), and com b inations of failures which have been subject to m a ndatory corrective actions, following inservice findings, on products with a sim ilar fuel system designs.

b) Fuel tanks with high flam m a bility exposure tim e For fuel tanks with high flam m a bility exposure tim e, non-com p liant design
features and associated m a intenance actions identified by the system safety analysis that was conducted for the one tim e SFAR 88 design review will be used for establishing unsafe condition. These will be considered as unsafe conditions (i.e. strict com p liance to §§ 25.981 (a) and (b) (Am e ndm ent 25-102) and 25.901 using guidance in AC 25.981-1 m u st be found) and m u st be addressed by corrective action (i.e. AD).

Elem ent 3. Unacceptable service experience – all tanks For any tank (either high or low flam m a bility exposure tim e), all failures identified in service, that result in therm a l or electrical energy dissipation into the fuel tank system which could create an ignition hazard, or m a king fuel tank safety protection devices inoperative (e.g. fuel pum p canister, wire sleeving, bonding lead), are considered
unsafe conditions and m u st be addressed by corrective action (i.e. AD). Those
failures m a y result from equipm ent or com ponent failures, aging, as well as

5 of 16production or m a intenance errors, and inappropriate flight deck actions (such as, leaving fuel pum ps “ON” beyond their design usage).

Elem ent 4. Determ ination of the flam m a bility exposure tim e of each fuel tank Typically, alum inum wing tanks without any heating source are considered to have a
low flam m a bility exposure tim e. However, several param e ters including tank
volum e, geom etry, am ount of fuel rem a ining from the previous flight, am bient

tem p erature, tem p erature of loaded fuel, tim e on the ground, m a y influence
flam m a bility exposure tim e. Determ ination of flam m a bility exposure tim e of each fuel tank is required. In the absences of any substantiating analysis, all tanks shall be considered as a “high flam m a bility exposure tim e” fuel tank. Table 2, “Flam m a bility Exposure Tim e Determ ination,” is attached at the end of this m e m o randum , which

sum m a rizes the following discussion on determ ining fuel tank flam m a bility exposure
tim e.

Acceptable m e thod of analysis
In the absence of another m e thod agreed to by the FAA, the following guidance is considered an acceptable m eans of establishing the flam m a bility exposure tim e of
each fuel tank. Other m e thods m a y be proposed, but shall be approved by the FAA. For the purpose of the assessm ent of in-service aircraft, this three-step approach has been harm onized between FAA and JAA.

Low Flammability Exposure Time Tank Determination:

Step 1.
Does the tank have characteristics of a Low Flam m a bility Exposure Tim e tank, as
def i ned below, by inspection and qualitative design review?

If Yes, tank is a Low Flam m a bility Exposure Tim e Tank, if No, go to Step 2

Step 2.
Can the tank m eet the abbreviated quantitative criteria f o r a Low Flam m a bility Exposure Tim e Tank?

If Yes, Tank is a Low Flam m a bility Exposure Tim e Tank, if No, go to Step 3

Step 3.
Can the tank m eet the Low Flam m a bility Exposure Tim e Tank Criteria using the FAA Monte-Carlo analysis and ground fuel tem p erature lim it?

If Yes, Tank is a Low Flam m a bility Exposure Tim e Tank, If No, Tank is a High
Flam m a bility Exposure Tim e Tank.

Characteristics of a Low Flammability Exposure Time Tank

For Step 1: The qualitative design review criteria for a low flam m a bility exposure tim e tank

are:

6 of 161. During 4 hour operation on the ground on a 100 deg F day, a fuel tem p erature rise of less than 10 Deg F above am bient 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
alum inum 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 flam m a bility exposure tim e tank

are: 1. During 4 hour operation on the ground on a 100 deg F day, a fuel tem p erature rise of less than 10 Deg F above am bient 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 em pty, starting from a fuel tem p erature of 60 Deg F, and TAT of –20 Deg F,

And
3. The fuel tem p erature at the end of a m a xim u m range cruise shall be within 10 Deg F of TAT.

For Step 3:
The criteria for a low flam m a bility exposure tim e tank are:
1. Has a Fleet Average Flam m a bility exposure tim e of no m o re than 7% using
the FAA Monte-Carlo Model m e thod.

And
2. A fuel tem p erature rise of less than 20 Deg F on the ground starting with a 100 deg F am bient tem p erature and m i nim u m 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 therm a l characteristics of the tank in question, and if it m e t the criteria above, the tank would be considered a low
flam m a bility exposure tim e tank. If a tank does not m eet the above criteria it will be classified as a high flam m a bility exposure tim e tank for the purpose of m a king
unsaf e condition f i ndings. The Monte-Carlo m odel uses a f l am m a bility 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

seem ed appropriate. The m odel is an excel spreadsheet, and is downloadable from the FAA web site, http://qps.airweb.faa.gov/sfar88flam e x . It is required to use
version 5a or later of the Monte-Carlo m odel and provide docum entation of how the

7 of 16analysis was perform e d. See attachm e nt 3 for guidance on how the docum entation should be perform e d.

Flammability Reduction or Effects of Ignition Mitigating Devices
A suitable flam m a bility reduction system such as inerting, or an ignition m itigating
device such as foam , etc, m a y be used for ignition source m itigation. High flam m a bility exposure tim e fuel tanks can be treated as low flam m a bility exposure tim e fuel tanks for the purpose of SFAR 88 AD determ ination, if the m itigation 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 flam m a ble fluid leakage zone is to assum e that flam m a ble vapors m a y be present in the zone and to

m i nim i ze the probability of ignition of the vapors in accordance with § 25.863(a). This has typically been accom p lished by using various standards of explosion-proof

com ponents and good design practices.

The existence of an unsafe condition should be determ ined based on the probability of a leak (taking into account in-service experience, and m itigating factors such as using double walls, protective coating, etc.), and considering the potential ignition sources and the design precautions taken in the area (com ponent qualification, drainage, ventilation).
Unsafe conditions m u st be addressed by corrective action (i.e. AD).

Maintenance Considerations Results of safety assessm ents m a y define m a ndatory m a intenance actions needed to prevent an unsafe conditions. These m a intenance actions m u st be included in the
lim itation section of the instructions for continued airworthiness. Som e m a nufacturers have developed airworthiness lim itations (referred to as “Fuel System Lim itations” by

som e m a nufactures) to differentiate these lim itations from structural lim itations. The
lim itations and critical design configuration control lim itations (CDCCL) m u st be addressed in accordance with the standards of § 25.981(b) (Am e ndm ent 25-102) to ensure fuel tank system protective features are m a intained and/or controlled.

Effect of Policy The general policy stated in this docum ent does not constitute a new regulation or create

a new norm , but is for the purpose of clarifying the considerations for determ ining an unsafe condition using the findings from the one tim e fuel tank safety review conducted
for SFAR 88. These criteria are intended to com p lim ent the associated SFAR 88 advisory

m a terial and help determ ine which corrective action should or should not be introduced on in-service Airplanes. The office that im plem ents policy should follow this policy when applicable to the specific SFAR 88 project. W h enever an applicant' s proposed

m e thod of com p liance is outside this established policy, it m u st 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 inform ation
when m a king determ ination of unsafe conditions for the fuel system design features

8 of 16identified from the system safety analysis conducted for the one tim e SFAR 88 design
review.

If you have further questions, the person on m y staff m o st fam iliar with this issue is
Mr. Dennis Kam m e rs (425-227-2956).

/s/ 

## Michael J Kaszycki

for Vi L. Lipski

9 of 16cc: 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 Ce rtification Office, ANE-150 Manager, New York Aircraft Certification Office, ANE-170 Manager, Ft. W o rth Airplane Certification Office, ASW

- 150 Manager, Ft. W o rth Special Certification Office, ASW

- 190 Manager, Atlanta Aircraft Ce rtification Office, ACE-115A Manager, W i chita Aircraft Certification Office, ACE-115W Manager, Chicago Aircraft Ce rtification 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

10 of 16TABLE 1SFAR 88 Unsafe Condition Determination CriteriaELEMENT 4: Flammability Exposure TimeAHigh Flammability ExposureTime tanksBHigh Flammability Exposure Timetanks driven to LowFlammabilityExposure Time tanks through inertingor other meansCLowFlammabilityExposure Time tanksELEMENT 1:Evaluation for SingleFailuresUnsafe if:Foreseeable Single Failures Jeopardize Safe OperationRequired Action:All identified single failure conditions must be addressed by corrective action (i.e. AD)ELEMENT 2:Evaluation forCombinations ofFailures“Compliance”Unsafe if:Any noncompliance to§§ 25.981 (a) or (b) (Amendment25-102) or 25.901 using guidancein AC 25.981-1Required Action:It is expectedthat any noncompliance findingwill be considered as an unsafeconditions and addressed bycorrective actions (i.e. AD)Unsafe if:Known Combinations of Failures Jeopardize SafeOperationRequired Action:All known combinations of failures must beaddressed by corrective action (i.e. AD).ELEMENT 3:Evaluation forIn-Service ExperienceUnsafe if:In-service failures exist that either a) dissipate energy into tank/create ignition sources, or b)compromise fuel tank safety protection devicesRequired Action:All of the in-service failures must be addressed by corrective action (i.e. AD)Attachment 111 of 16Table 2Flammability Exposure Time DeterminationStep 1Can the tank satisfythe Low Flammabilityexposure time characteristics by qualitativeinspection and design review?If Yes, tank is a Low Flammability exposuretime tank, if No, go to Step 2Step 2Can the tank meet the Quantitative criteria for aLow Flammability exposure time tank?If Yes, Tank is a Low Flammability exposuretime tank, if No, go to Step 3Step 3Can the tank meet the Low Flammabilityexposure time tank Criteria using the FAAMonte-Carlo analysis?If Yes, Tank is a Low Flammability exposuretime Tank, If No, Tank is a High Flammabilityexposure time tankCharacteristics of a LowFlammability Exposure Time TankLow Heat Input:Step 1: Qualitative Inspection &Design Review:No or very small airplane based heat sources (A fuel temprise of less that 10 deg Fabove ambient on the ground, for a 100 deg F day with an 80% full fuel load)internal/external to the tank, including heat transfer froman adjacent tank thatcould heat the tank, andAbility to reject heat quickly to outside air. A conventional Aluminumskinstringer construction, high percentage (80 to 90%) of surfaces exposed to freestreamairStep 2: Quantitative Determination:Less than 10 Deg F above ambient temperature rise on the ground over many hourswith an 80% full fuel load, andInitial cruise cooling rates of 20 Deg F per hour, with tank 80% Full, and 35 Deg Fper hour with tank empty, starting from60 Deg F and a TAT of –20 Deg F, andEnd of long cruise tank temperature within 10 Deg F of TATStep 3: Monte-Carlo Method:Has a Fleet Average Flammability exposure time of no greater than 7% using theFAA Monte-Carlo Model, andA fuel temperature rise of less than 20 deg F on the ground starting with a 100 degF dayAttachment 212 of 16

### Attachment 3

Documenting the Results of the Flammability Exposure Time Determination

This attachm e nt provides guidance on how TC and STC holders should assem b le
docum entation for flam m a bility exposure tim e determ ination analysis, and when these
results should be subm itted.

Submittal Options
The results m a y be subm itted to the FAA using any of the options shown below:

Option 1:
Subm it the flam m a bility exposure tim e determ ination results in a self contained
docum ent or report. The report should be subm itted under appropriate cover
letter to the FAA.

Option 2:
The results m a y be included as an added section of, or appendix to a revised copy
of the docum ent(s) originally subm itted for com p liance with SFAR 88. This new section should be clearly delineated from the other sections of the docum ent. If this option is used, none of the original SFAR 88 non-com p liance findings m a y be changed based on the fuel tank flam m a bility exposure tim e

. I n o t h e r w o r d s , the flam m a bility exposure tim e results may not be used to re-visit the original

non-com p liances and apply a risk/probability analysis to show com p liance with § 25.981 (a) and (b) Am endm ent 25-102 . The flam m a bility exposure tim e results

m a y only be used to determ ine if m a ndatory action is required for a given noncom p liance. The revised report should be subm itted under appropriate cover
letter to the FAA.

Option 3:
The TC or STC holder m a y subm it the results in any other reasonable, form ally
docum ented form at. If this is the case, please ask them to contact the FAA and explain their proposed m e thod of subm ittal.

Option 4:
The TC or STC holder m a y choose to not subm it the results of a flam m a bility exposure tim e determ ination analysis. In this case, for the purposes of
determ ining m a ndatory actions, the FAA should assum e the fuel tank is a high
flam m a bility exposure tim e fuel tank.

What to Include in the Documentation

The following should be included in the docum entation of the flam m a bility exposure
tim e determ ination analysis.

13 of 161. A brief sum m a ry of the fuel tank configur ation. This should include both a schem a tic of the fuel tank system , and diagram s and/or photographs showing the fuel tanks (external views). If this has already been done as part of the Decem ber 6, 2002
SFAR 88 docum ent subm ittal, it is acceptable to refer to the appropriate section(s) of
those docum ents.

2. The flam m a bility exposure tim e determ ination m e thod/step used, and the results for
each fuel tank. These should be docum ented as follows:

If Step 1 is used:

W h at to include in docum entation:

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 f u el tank construction (i.e. alum inum skin/stringer construction)

2. For fuel tank stabilization tem p eratures, please provide the test data, or heat transfer analysis m e thods used to derive these

• If test data is provided, a sim p le plot will suf f i ce. 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 m a tch the production airplane.)

• If test data is used, but a correction m e thod is applied to em ulate a particular

am bient tem p erature (in the case of Step 1, 100 degrees F), please clearly indicate this. Also provide a detailed description of the m e thod used to correct the test data to the equivalent of a 100 degree F am bient day.

• If heat transfer m e thods will be used, please provide a suitable description of
the m e thods used, including the developm ent of the various inputs such as convective coefficients, and assum e d heat rejection of any airplane based heat

sources.

3. The Flam m a bility Exposure Tim e Classification Statem ent: :

• Exam ple Statem ent: “Following the FAA-JAA Harm onized Fuel Tank
Flam m a bility Exposure Tim e Determ ination Methodology, (Com pany Nam e )
has determ ined this f u el tank m a y be classif i ed as a Low Flam m a bility Exposure Tim e Fuel Tank.”

4. Any other descriptive m a terial, or data deem ed appropriate

14 of 16If Step 2 is used:

W h at to include in docum entation:

Sam e as for Step #1

If Step 3 is used:

W h at to include in docum entation

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 f u el tank construction (i.e. alum inum 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 tem p eratures and tim e constants, please provide the test data, or heat transfer analysis m e thods used to derive these.

• If test data is provided, a sim p le plot will suf f i ce. 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 m a tch the production airplane.) The FAA will need to assess the integrity of this data, as applied to the developm ent of input for the
Monte-Carlo m odel.

• If heat transfer m e thods will be used, please provide a suitable description of
the m e thods used, including the developm ent of the various inputs such as convective coefficients, and assum e d 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 m i ssion length profiles to closer m a tch a specific m odel). c) Describe any testing/validation of the m odel after the changes were m a de

15 of 1616 of 16 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.