1170 Peachtree Street

Suite 1200

Atlanta GA 30309

Phone: 404-346-7175

www.jetairegroup.com

August 9, 2010

Ref. 9027-100-005

Mr. Ali Bahrami

Manager, Transport Airplane Directorate

Federal Aviation Administration

Aircraft Certification Service Seattle ACO

1601 Lind Avenue, SW

Renton, WA 98055-4056

Mr. Bahrami:

Petitioner Jetaire Aerospace & Technology, Inc. (hereinafter "Jetaire" or "Petitioner") hereby requests an 

exemption from certain requirements of Title 14, Code of Federal Regulations (CFR) 25.981(a)(3), as 

amended by Amendments 25-102 and 25-125, for its innovative use of reticulated polyurethane foam 

technology as a fire and ignition source suppressant in certain transport category aircraft fuel tanks. The 

proposed exemption, if granted, would allow Petitioner to enhance the safety of aircraft subject to the 

requirements of 14 C.F.R. 25.981 ("Rule 25.981") to a much greater degree than currently approved 

methods of compliance utilizing a combined use of transient suppression devices ("TSDs") and "gas 

inerting" techniques. In particular, granting of this Petition will allow Jetaire to certify and complete 

modification of auxiliary fuel tanks of models B727, B737 and DC-9 aircraft with auxiliary fuel tanks 

installed per various Supplemental Type Certificates. Granting of the partial exemption would permit 

complete compliance with Rule 25.981 by utilizing reticulated foam technology as a means of 

compliance to 25.981. 

Jetaire Aerospace & Technology, Inc. has at least three (3) clients/aircraft owners whose current 

projects have are at various stages of completion and are awaiting approval and certification of the RPF 

method to return their aircraft to airworthiness. Until such time as this exemption is granted, these 

owners and similar aircraft owners that have gained extensions of time for compliance with Rule 25.981, 

are unable to fly their aircraft. Obviously, extended downtime in which these aircraft cannot be used is 

endured at great and unnecessary expense.
Mr. Ali Bahrami

Manager, Transport Airplane Directorate

Federal Aviation Administration

Page 2

Therefore, Jetaire requests the FAA to exempt Petitioner from full compliance with 14 CFR 

25.981(a)(3) requiring the demonstration of a complete elimination of the possibility of an ignition 

source in the fuel tank or fuel tank system as it pertains to auxiliary fuel tanks. 

If there are any questions concerning this matter I can be reached via e-mail at 

mwilliams@jetairegroup.com or by cellular at 770-356-6562. 

Sincerely,

Michael D. Williams

President

Enclosures

Cc: Melvin Taylor-Atlanta ACO
1

August 9, 2010

Mr. Ali Bahrami

Manager, Transport Airplane Directorate

Aircraft Certification Service Seattle ACO

1601 Lind Avenue, SW

Renton, WA 98055-4056

RE: Petition for Partial Permanent Exemption from 14 C.F.R. 25.981 regarding auxiliary fuel tanks 

for aircraft models B727, B737 and DC-9. 

PETITION FOR PARTIAL PERMANENT

EXEMPTION PERTAINING TO 14 C.F.R. 25.981

Petitioner Jetaire Aerospace & Technology, Inc. (hereinafter "Jetaire" or "Petitioner") hereby 

requests an exemption from certain requirements of Title 14, Code of Federal Regulations (CFR) 

25.981(a)(3), as amended by Amendments 25-102 and 25-125, for its innovative use of reticulated 

polyurethane foam technology as a fire and ignition source suppressant in certain transport category 

aircraft fuel tanks. The proposed exemption, if granted, would allow Petitioner to enhance the safety of 

aircraft subject to the requirements of 14 C.F.R. 25.981 ("Rule 25.981") to a much greater degree than 

currently approved methods of compliance utilizing a combined use of transient suppression devices 

("TSDs") and "gas inerting" techniques. In particular, granting of this Petition will allow Jetaire to certify 

and complete modification of auxiliary fuel tanks of models B727, B737 and DC-9 aircraft with auxiliary 

fuel tanks installed per various Supplemental Type Certificates. Granting of the partial exemption would 

permit complete compliance with Rule 25.981 by utilizing reticulated foam technology.

Petitioner requests relief from the following regulation:

14 C.F.R. 25.981(a)(3), Fuel tank ignition prevention, as amended by Amendments 25-102 and 25-125:

"(a) No ignition source may be present at each point in the fuel tank or fuel tank 

system where catastrophic failure could occur due to ignition of fuel or vapors. This must 

be shown by: 

(3) Demonstrating that an ignition source could not result from each single failure, 

from each single failure in combination with each latent failure condition not shown to be 

extremely remote, and from all combinations or failures not shown to be extremely 

improbable. The effects of manufacturing variability, aging, wear, corrosion, and likely 

damage must be considered."

Rule 25.981 has two (2) relevant amendments that are applicable to Jetaire's demonstration of an 

"acceptable level of safety" within its ELOS document; Amendment 25-102 and Amendment 25-125. 

Admittedly, 25-102 was replaced by 25-125; however, 25-125 primarily effects amendments to Rule 

25.981(b) and retains the language of Amendment 25-102 to Rule 25.981(c). The amended language of 

Rule 25.981(c) states as follows:

"(c) Paragraph (b) of this section does not apply to a fuel tank if means are provided to 

mitigate the effects of an ignition of fuel vapors within that fuel tank such that no damage 

caused by an ignition will prevent continued safe flight and landing (emphasis added)."
2

The petitioner supports its request with the following information:

I. Background

The use of reticulated polyurethane foam ("RPF") to prevent ignition and explosion within 

aircraft fuel tanks has been in use for more than thirty-five (35) years. As a result of its long history of use 

in military applications, there is substantial quantitative and qualitative data that supports its explosion 

mitigation effect under conditions that are more stringent and hazardous than ordinary commercial flight 

operations. Further, Chapter 12 of Advisory Circular 25.981-2A states:

"a. [O]ne means to meet §25.981 is to protect a tank from structural and systems damage 

that could prevent continued safe flight and landing of the airplane. This alternative 

recognizes that an applicant may choose to accept a high flammability exposure in a 

given tank and to provide additional protection to extinguish or suppress an explosion in 

a tank if an ignition occurs.

b. The use of appropriate foams to fill the fuel tank and thereby control the pressure rise 

following an ignition of the fuel vapor/air mixture has been demonstrated to be effective 

by the United States Air Force and other military forces. Foams are in use on several 

civilian transport category airplane types. Detailed design information regarding use of 

reticulated polyurethane safety foam for explosion suppression is provided in the report 

referenced in paragraph 4d(1) of this AC. The applicant may use such a foam installation 

to satisfy the requirement of §25.981 (emphasis added). The foam type should be 

demonstrated to be effective in suppressing explosions to a level where structural and 

system damage is prevented. The applicant should:

(1) Provide data on the foam, including material, pore size, and intended 

method for installing the foam in the tank.

(2) Address the potential for, and the effects of, degradation of the foam, 

from any environmental effects and long term aging, on both the airplane and engine fuel 

systems. If the foam has a limited useful life, particular installation requirements, or 

other features that are essential for the IMM to perform its intended function, they should 

be identified as CDCCLs.

(3) Address the effects of the foam installation on fuel system performance, 

including engine feed, venting, unusable fuel, sump capacity, expansion space capacity, 

fueling, and defueling, including the effect of the foam on electrostatic buildup in the 

tank.

(4) Address the effect of the foam installation on the airplane fuel system, as 

well as the auxiliary power unit (APU) and engine fuel systems, and develop 

maintenance procedures to ensure the foam is correctly installed, both initially and when 

reinstalled, if removed for access to the tank."

 

Advisory Circular 25.981-2A clearly states in paragraph b. that a foam installation may be used to satisfy 

the requirements of §25.981 without reference to an isolated subparagraph of the Rule. In other words, a 

foam installation may satisfy the complete requirements of Rule 25.981 if the four (4) enumerated 

conditions are meet by an applicant. Jetaire has demonstrated that the foam application utilized in 

auxiliary tanks in B727, B737 and DC-9 model aircraft is effective in suppressing explosions to a level 
3

where structural and system damage is prevented and all four of the conditions stated in the AC are 

addressed. 

When measuring the acceptable level of safety offered by RPF in satisfying the purpose of Rule 

25.981, particularly revealing and helpful studies involve the examination of RPF removed from aircraft 

fuel tanks after years of use. One such study, dated July 17, 1998, entitled Foam, compiled by the Fuel 

Tank Foam and Expanded Metal Products Task Group, Task Group 4 for the Aviation Rulemaking 

Advisory Committee demonstrated that multiple "sparks" had occurred within the aircraft fuel tanks and 

had recorded burns on the surface of RPF present in the tanks. This evidence revealed that although 

ignition sparks had occurred within the tanks, there was no recorded incidence of a catastrophic 

explosion. In other words, ignition sparks entering the tanks were prevented from escalation to an 

expanded flammability and explosion by the presence of the RPF foam. No catastrophic failures 

resulting in a fuel tank explosion had occurred.

II. Public Interest

Full compliance to 25.981(a)(3) with respect to the demonstration of a complete elimination of 

the possibility of an "ignition source that could result from each single failure, from each single failure in 

combination" in auxiliary fuel tanks for the B727, B737 and DC-9 models will require significant 

redesign and modifications to the fuel tank, electrical systems and structure with no measurable 

improvements to aircraft safety. In addition to introducing additional complexity in the manufacturing, 

quality and maintenance procedures, a redesign of the proven technologies described above will add 

significant cost and schedule impact to the Model B727, B737 and DC-9 owners.

When measuring 14 CFR Part 25 contains the minimum design standards for type certification of 

transport category airplanes. The primary intent of these regulations is to ensure that airplane 

manufacturers provide the appropriate design features to meet the standards necessary to protect the 

traveling public. Clearly, there is a requirement "in the public interest" and in the interest of safety to 

provide Regulatory guidelines for certification. However, it is also very clear that these regulations are 

intended to regulate the certification of "commercial" airplanes which are "for hire" to the general public.

While the majority of these regulations are applicable to any aircraft regardless of its intended use, a few 

are obviously intended to regulate situations that are specific to a commercial airline or "for hire" 

operation. When a transport category airplane is operated under 14 CFR Part 91 or Part 125 as "private 

use, not-for hire", some of the Part 25 regulations contain design criteria that are inappropriate, or are not 

compatible with the type of operation and the intended use of this airplane.

FAA requirements against the Petitioner's use of reticulated polyurethane foam in auxiliary tanks 

for compliance with this rule will prevent Jetaire and its customers/aircraft owners from certifying the 

aircraft on a timely and competitive schedule. This puts Jetaire at an unfair disadvantage with its 

competitors. Moreover, the use of reticulated polyurethane foam has been shown to increase the level of 

safety intended by Rule 25.981 to a degree substantially greater than that achieved by the use of TSDs 

and the combined use of TSDs and gas inerting techniques in combination. Particularly, the probability 

of failure of a static system, such as foam, is far less than the use of electronics and dependent systems 

such as transient suppression. Many private owners of B727, B737 and DC-9 aircraft around the US and 

the world that use their aircraft for business needs are anticipating the certification of their aircraft with 

the safer RPF alternative. Failing certification, these owners would be forced to find more costly and less 

safe alternatives.
4

III. Effect on Safety

The use of reticulated polyurethane foam installed in aircraft auxiliary fuel tank systems is 

intended to fully comply with 14 CFR 25.981, as amended per amendment 102, and meet flammability 

and ignition source requirements. The Air Force has successfully been using the conductive type 

reticulated foam since the 1980’s and has not had one ignition source incident other than when the RPF 

was inadvertently left out of a fuel nacelle. 

Reticulated polyurethane foam is a FAA approved Ignition Mitigation Means (Chapter 12 of AC 

25.981-2A) to meet § 25.981 by protecting the auxiliary tanks from structural and systems damage that 

could prevent continued safe flight and landing of the airplane. This alternative recognizes acceptance of 

a higher flammability exposure in a given tank and provides additional protection to extinguish or 

suppress an explosion in a tank if an ignition occurs. The tanks as currently installed in the pressurized 

Class D Baggage compartments of the DC-9 have been analyzed utilizing the Fuel Tank Flammability 

Assessment program that applies Monte Carlo simulations to determine Flammability exposure. The 

analysis showed that the unmodified tanks had an exposure of less than 3%. With the addition of the RPF 

the flammability exposure was determined to be insignificant.

In order to suppress an ignition source, the use of appropriate foams to fill the fuel tank and 

thereby control the pressure rise following an ignition of the fuel vapor/air mixture has been demonstrated 

to be effective by the United States Air Force (USAF) and other military forces. Foams are in use on 

several civilian transport category airplane types. Detailed design information regarding the use of 

reticulated polyurethane safety foam for explosion suppression is provided in Report MIL-B-83054, 

Baffle and Inerting Material, Aircraft Fuel Tank (March 1984). The report demonstrates that proper 

application of a foam installation satisfies the requirements of § 25.981. RPF installed in aircraft auxiliary 

tanks has demonstrated, in accordance with MIL-F-87260-A, to be effective in suppressing explosions to 

a level where structural and system damage is prevented. This conclusion was substantiated by:

(1) Providing data on the foam, including material, pore size, and intended method for 

installing the foam in the tank; 

(2) Addressing the potential for, and the effects of, degradation of the foam, from any 

environmental effects and long term aging, on both the airplane and engine fuel systems. 

Defining in the CDCCL the foams limited useful life, particular installation requirements, 

and other features that are essential for the IMM to perform its intended function; and 

(3) Addressing through test and analysis the effects of the foam installation on fuel system 

performance, including engine feed, venting, unusable fuel, sump capacity, expansion 

space capacity, fueling, and defueling, including the effect of the foam on electrostatic 

buildup in the tank.

The fuel tanks with the RPF installed endured a rigorous System Safety Analysis that showed that, with 

the addition of the RPF and the application of specific ignition source prevention techniques outlined in 

AC 25.981-1C paragraphs 9 & 10 the auxiliary tanks will:

(1) Not cause an ignition source for each single failure, regardless of the probability of 

occurrence; 

(2) Ensure that each single failure, regardless of the probability of occurrence, in 

combination with any latent failure condition not shown to be at least extremely remote 
5

(i.e., not shown to be extremely remote or extremely improbable), will not cause an 

ignition source; and

(3) Ensure that all combinations of failures not shown to be extremely improbable will not 

cause an ignition source.

Furthermore, the RPF has demonstrated that the material can provide a number of added benefits beyond 

that of internal ignition source and flammability protection. Such added benefits include reduction in 

slosh and vibration effects and the entrapment of foreign objects and lose debris.

Consequently, taking into account all aspects of fuel tank flammability reduction and ignition 

suppression for which the auxiliary fuel tanks are compliant, and regarding the low flammability exposure 

as a mitigation factor for the absence of a third protection against an ignition source, Jetaire believes 

granting this exemption has no impact on safety.

IV. Timing aspects of request

Jetaire Aerospace & Technology, Inc. has at least three (3) clients/aircraft owners whose current 

projects have been substantially completed and are awaiting only approval and certification of the RPF 

method to return their aircraft to airworthiness. Until such time as this exemption is granted, these owners 

and similar aircraft owners that have gained extensions of time for compliance with Rule 25.981, are 

unable to fly their aircraft. Obviously, extended downtime in which these aircraft cannot be used is 

endured at great and unnecessary expense.

Jetaire has previously demonstrated that full compliance with Rule 25.981 has been satisfied by 

the use of reticulated polyurethane foam in auxiliary fuel tanks, in that, the use of foam eliminates the 

possibility of catastrophic failure resulting from an ignition in the fuel tanks or fuel tank systems to a 

greater degree than that of an extreme improbability without the use of TSDs.

Therefore, Jetaire requests the FAA to exempt Petitioner from full compliance with 14 CFR 

25.981(a)(3) requiring the demonstration of a complete elimination of the possibility of an ignition source 

in the fuel tank or fuel tank system as it pertains to auxiliary fuel tanks. 

V. International Operations

Owners of the subject aircraft frequently use the aircraft in international travel; therefore, Jetaire 

requests the FAA to include use outside of the United States. Due to the small number of aircraft and the 

fact that they are operated under 14 CFR Part 91 or Part 125 as "private use, not-for hire", the approval of 

the exemption for international use has an insignificant impact on the flying public.

Before Jetaire extends the requested exemption for use outside the United States, it will verify 

that the exemption would be in compliance with the Standards of the International Civil Aviation 

Organization (ICAO). If it would not, but we still believe it would be in the public interest to allow you to 

do so, we will file a difference with ICAO. However, a foreign country still may not allow an aircraft to 

operate in that country without meeting the ICAO standard.
6

VI. Conclusion

Jetaire requests that its innovative use of reticulated polyurethane foam to mitigate ignition within 

auxiliary fuel tanks and fuel systems of B727, B737, and DC-9 aircraft be exempted from compliance 

with Rule 25.981(a)(3) as described above. The granting of Jetaire's request will enhance the safety of 

aircraft subject to compliance with 14 C.F.R. 25.981 in excess of the level of safety achieved by the use 

of transient suppression devices and the combined use of transient suppression devices and gas inerting 

procedures. Requiring the addition of transient suppression devices to Jetaire's proposed use of 

reticulated polyurethane foam would not further increase or enhance the level of safety in the fuel tanks or 

fuel systems to achieve the safety levels intended or dictated by Rule 25.981. The requirement of 

transient suppression devices in addition to the use of reticulated polyurethane foam is, therefore, an 

ineffective and unnecessary expense to the public that does not significantly impact or increase the level 

of safety achieved by the use of reticulated polyurethane foam.