ARAC WG Report Format

Category 3 Items

1 - What is underlying safety issue addressed by the FAR/JAR? [Explain the underlying safety 

rationale for the requirement. Why does the requirement exist?]

In order to prevent unsafe conditions from developing due to an on-board fire, or to the 

use of built-in systems intended to combat them, FAR/JAR 25.851(b) requires that builtin fire extinguishers be installed so as to be non-hazardous to airplane occupants who are 

likely to be exposed to them, that the discharge of the extinguisher not cause structural 

damage, and that the capacity of the systems be adequate for any fire likely to occur in the 

designated compartment.

2 - What are the current FAR and JAR standards? [Reproduce the FAR and JAR rules text as 

indicated below.]

Current FAR text: (Amendment 25-74, “Airplane Cabin Fire Protection”, published in the Federal 

Register, 56 FR 15450, April 16, 1991)

(b) Built-in fire extinguishers. If a built-in fire extinguisher is provided-

 (1) Each built-in fire extinguishing system must be installed so that-

(i) No extinguishing agent likely to enter personnel compartments will be 

hazardous to the occupants; and 

(ii) No discharge of the extinguisher can cause structural damage. 

(2) The capacity of each required built-in fire extinguishing system must be 

adequate for any fire likely to occur in the compartment where used, 

considering the volume of the compartment and the ventilation rate.

 

Current JAR text: (Change 14, May 27, 1994)

(b) Built-in fire extinguishers. If a built-in fire extinguisher is provided-

 (1) Each built-in fire extinguishing system must be installed so that-

(i) No extinguishing agent likely to enter personnel compartments will be 

hazardous to the occupants; and 

(ii) No discharge of the extinguisher can cause structural damage. 
(2) The capacity of each required built-in fire extinguishing system must be 

adequate for any fire likely to occur in the compartment where used, 

considering the volume of the compartment and the ventilation rate.

3 - What are the differences in the standards and what do these differences result in?: 

[Explain the differences in the standards, and what these differences result in relative to (as applicable) 

design features/capability, safety margins, cost, stringency, etc.]

There are no differences in the written standards. There are no harmonization issues 

related to section (b)(1). 

The remainder of this report will only address the harmonization issues related to the 

application of section (b)(2) to cargo compartments with built in fire extinguishing 

systems. 

4 - What, if any, are the differences in the means of compliance? [Provide a brief explanation 

of any differences in the compliance criteria or methodology, including any differences in either criteria, 

methodology, or application that result in a difference in stringency between the standards.]

Section 25.851(b) is intended to ensure that the built-in fire extinguishing system does not

introduce a hazard to occupants or the airplane structure, and that the system is adequate 

to control any fire likely to occur. The ambiguity present has resulted in differing 

interpretations of the intent of 

“... capacity of each required built-in fire extinguishing system must be adequate 

for any fire likely to occur in the compartment where used, considering ...” 

which has resulted in different compliance test success criteria being imposed on 

applicants for FAR certification as opposed to JAR certification. 

Most Transport Category airplane cargo compartment fire extinguishing systems utilize 

Halon 1301 as an extinguishing agent. This agent is stored as a liquid in pressurized 

containers, but is dispersed in the compartment when needed as a dense gas. Laboratory 

tests conducted by the FAA Technical Center in Atlantic City, New Jersey (Reference 

FAA-RD-71-68, November 1971) concluded that a three to five percent by volume 

concentration of Halon 1301 in combination with ventilation shutoff can effectively 

control cargo fires in Class C compartments. Since that time the consensus of U.S. and 

European airplane manufacturers, the FAA and JAA has been that to show compliance 

with the subject FAR and JAR, Halon cargo fire extinguisher systems must demonstrate 

the capability to provide an initial concentration of 5% by volume in an empty 

compartment, and maintain a 3% by volume concentration for the time period specified 

for the airplane’s operational requirements.

In summary, it may be stated that FAA and JAA and applicants have adopted a two step 

method to certify Halon 1301 cargo fire suppression systems. First an initial use of Halon 

1301 is provided at a concentration of five percent by volume in order to knock down a 

cargo fire. Subsequently, a second discharge via either a metered or discrete system is 

used to ensure that subsequent concentration levels should not drop below three percent 
by volume for the remainder of the flight in order to suppress a cargo fire until it can be 

completely extinguished by ground personnel following a safe landing. However, in 

demonstrating compliance to FAR/JAR 25.851(b) using this approach the FAA and JAA 

have utilized different methods of evaluating the concentration data. 

Historically the FAA policy has accepted the use of a volumetric averaging of sensor data 

to show compliance. The FAA has also accepted in the past the use of CO2 decay tests to 

determine the cargo compartment leakage in flight, with the Halon concentration 

determined analytically. This also resulted in approval of an average value for Halon 

concentration. Current JAA policy does not accept averaging methods but requires that 

each individual sensor display the required concentration. Compliance with this standard 

has been required by Certification Review Item in some recent JAR validation programs. 

Testing at the FAA Technical Center and other data from standardized fire extinguishing 

evaluation tests indicates that the use of averaging techniques may not substantiate that 

there are adequate concentration levels of fire extinguishing agent throughout the 

compartment to effectively suppress a cargo fire. If a cargo fire occurred, and was 

subsequently suppressed by Halon 1301, the core of the fire could remain hot for a period 

of time. If the local concentration of Halon 1301 in the vicinity of the fire core dropped 

below three percent by volume and sufficient oxygen is available, reignition could occur. 

FAA testing has shown that when the Halon 1301 concentration level drops below three 

percent by volume and the cargo fire reignites, the convective stirring caused by the heat 

of the fire may be insufficient to raise the local concentration of Halon 1301 in the 

vicinity of the fire. As a result of this finding, the FAA philosophy began to change in the 

mid-1990’s and in letters (Reference 97-111-68, September 1997) to manufacturers 

expressed concern, i.e., “This averaging technique may allow the concentration level to 

drop below three percent by volume of individual sampling locations near the top of the 

cargo compartment while maintaining an average concentration level of three percent by 

volume throughout the cargo compartment.” Furthermore, in a Memorandum from the 

Transport Standards Staff to all Transport Airplane Aircraft Certification Offices 

(Reference 97-113-143, dated October 1997) expressed the position that “advise your 

applicants that the use of the technique of volumetric averaging to determine the 

minimum Halon 1301 concentration is questionable in light of the testing accomplished 

by the FAA’s Technical Center.” This concern was based upon testing conducted at the 

FAA’s William J. Hughes Technical Center (Reference DOT/FAA/AR-96/5, June 1996) 

which indicated that the volumetric averaging method may not provide adequate 

concentration levels of fire extinguishing agent to effectively suppress a cargo fire in all 

areas of the cargo compartment. 

5 – What is the proposed action? [Is the proposed action to harmonize on one of the two standards, a 

mixture of the two standards, propose a new standard, or to take some other action? Explain what action is 

being proposed (not the regulatory text, but the underlying rationale) and why that direction was chosen.]

The proposed action is to release joint Advisory material (FAA Advisory Circular and 

JAA Advisory Circular – Joint) which document acceptable methods for conducting 
flight tests and/or analyses which can be used for showing compliance to both FAR and 

JAR 25.851(b)(2). 

The advisory material should preclude the use of averaging techniques in compliance 

demonstrations for FAR/JAR 25.851(b)(2). The advisory material will define in general 

terms where gaseous extinguishing agent concentrations should be measured, and how 

the discrete measured data should be interpreted. There is no current plan to investigate 

the suitability of the 5% initial and 3% sustained concentration limits. The advisory 

material will also establish criteria for evaluating brief excursions in the concentration 

readings and if the data from a single measuring point can be time-averaged. Additional 

laboratory testing is recommended only if critical issues requiring advisory clarification 

cannot be resolved by other means.

6 - What should the harmonized standard be? [Insert the proposed text of the harmonized standard 

here]

No change to the wording of the FAR or JAR is proposed.

7 - How does this proposed standard address the underlying safety issue (identified under 

#1)? [Explain how the proposed standard ensures that the underlying safety issue is taken care of.]

The resulting Advisory Material will define an acceptable test and analysis method that 

will allow applicants to demonstrate how their proposed systems meet these minimum 

standards. This will prevent the approval of systems that might not maintain adequate 

extinguishing capability for the predicted fire threat. 

8 - Relative to the current FAR, does the proposed standard increase, decrease, or 

maintain the same level of safety? Explain. [Explain how each element of the proposed change to 

the standards affects the level of safety relative to the current FAR. It is possible that some portions of the 

proposal may reduce the level of safety even though the proposal as a whole may increase the level of 

safety.]

There is no change in the level of safety relative to FAR/JAR 25.851(b)(2). The proposed 

compliance standard will not increase the level of safety as established by the FAR/JAR. 

Section 25.851(b) is intended to ensure that the built-in fire extinguishing system does not

introduce a hazard to occupants or the airplane structure, and that the system is adequate 

to control any fire likely to occur. The proposed new guidance will, for the first time, 

provide specific guidance by defining the minimum agent concentration allowable at any 

measured location and ensure that the intent of the FAR/JAR is met. 

9 - Relative to current industry practice, does the proposed standard increase, decrease, or 

maintain the same level of safety? Explain. [Since industry practice may be different than what is 
required by the FAR (e.g., general industry practice may be more restrictive), explain how each element of 

the proposed change to the standards affects the level of safety relative to current industry practice. Explain 

whether current industry practice is in compliance with the proposed standard.]

Most new airplanes certified in the past two years have met the more stringent JAR 

compliance method. Those that have not were not required to do so by the certifying 

agency, but have demonstrated performance very close to the requirement. The proposed 

new guidance will, for the first time, provide specific guidance by defining the minimum 

agent concentration allowable at any measured location and ensure that the intent of the 

FAR is met.

10 - What other options have been considered and why were they not selected?: [Explain 

what other options were considered, and why they were not selected (e.g., cost/benefit, unacceptable 

decrease in the level of safety, lack of consensus, etc.]

The option of revising the text of the FAR and JAR was considered, but is not 

recommended. Any detailed compliance method developed in the near future would be 

specific to Halon 1301. This agent is scheduled for phase-out in the future, and other 

agents are under development. It would be inappropriate for this type of product specific 

detail to appear in the FARs and JARs. Creating a compliance standard based on existing 

test data and documented in advisory material is the most logical and cost-effective 

method of resolving this issue. Data available at this time indicates evidence that warrants 

the adoption of this change in compliance standards.

11 - Who would be affected by the proposed change? [Identify the parties that would be 

materially affected by the rule change – airplane manufacturers, airplane operators, etc.]

Manufacturers, modification centers, operators and system suppliers would bear 

additional costs to design, test and redesign fire extinguishing systems. Operators would 

bear additional costs to carry the weight of the extra extinguishing agent and to maintain a 

more complex distribution system. 

12 - To ensure harmonization, what current advisory material (e.g., ACJ, AMJ, AC, 

policy letters) needs to be included in the rule text or preamble? [Does the existing advisory 

material include substantive requirements that should be contained in the regulation? This may occur 

because the regulation itself is vague, or if the advisory material is interpreted as providing the only 

acceptable means of compliance.]

There is no existing advisory material on this subject, and no rule change is being 

proposed. 

13 - Is existing FAA advisory material adequate? If not, what advisory material should be 

adopted? [Indicate whether the existing advisory material (if any) is adequate. If the current advisory 

material is not adequate, indicate whether the existing material should be revised, or new material provided. 
Also, either insert the text of the proposed advisory material here, or summarize the information it will 

contain, and indicate what form it will be in (e.g., Advisory Circular, policy, Order, etc.)] 

The existing FAA advisory material is not adequate. Current practices are based on 

precedents set in the 1970’s, on certification plans negotiated for specific airplane 

projects by different Aircraft Certification Offices, and on various FAA policy memos 

and correspondence with Manufacturers. None of these sources adequately define a 

requirement to maintain a certain agent concentration at discrete points in the cargo 

compartments. 

Full-scale fire tests conducted over the years have used various methods to determine 

agent concentration, including analysis, discrete point measurement and averaging of 

discrete measurements. The current 5% initial and 3% sustained concentration standards 

are believed to derive from the FAA Technical Center test report FAA-RD-71-68 

referenced above. Since the test report shows no Halon measuring instrumentation, it is 

assumed the Halon concentration was calculated based on measurements of the amount of 

Halon discharged and the compartment volume. This can only provide a volumetric 

average concentration value. This is believed to be the origin of the practice of finding 

compliance using the averaging technique.

The JAA policy has been documented in recent Certification Review Items on specific 

airplane programs. The JAA has typically accepted the traditional location of agent 

concentration measuring points. The JAA currently requires that all of the sensors 

indicate a concentration at or above 5% initial and 3% sustained. These agreements are 

typically documented in the system certification plans and related correspondence.

The harmonized method of compliance should define in general terms where gaseous 

extinguishing agent concentrations should be measured, and what the minimum 

concentration should be at different locations within the compartment. Methods for 

certifying agent concentrations with loaded compartments should also be provided. 

Methods for evaluating data anomalies, effect of airplane maneuvering on test data, 

proposals for time averaging data at discrete points, and brief excursions below the 

required lower limits should also be provided. Additional testing should be considered if 

it is found necessary to resolve issues that might arise during the development of this 

Advisory Material.

14 - How does the proposed standard compare to the current ICAO standard? [Indicate 

whether the proposed standard complies with or does not comply with the applicable ICAO standards (if 

any)]

Due to their commitments as ICAO members, the US and all JAA-countries converted 

ICAO requirements into their airworthiness codes. So both the JAR and FAR 25 at least 

fulfill the ICAO minimum standards. As the proposed harmonized compliance method 

does not decrease the level of safety of FAR or JAR 25, it is in line with ICAO Annex 8 

"Airworthiness of Aircraft". 
15 - Does the proposed standard affect other HWG’s? [Indicate whether the proposed standard 

should be reviewed by other harmonization working groups and why.]

No other HWG’s are affected by this proposed compliance method harmonization.

16 - What is the cost impact of complying with the proposed standard? [Please provide 

information that will assist in estimating the change in cost (either positive or negative) of the proposed 

rule. For example, if new tests or designs are required, what is known with respect to the testing or 

engineering costs? If new equipment is required, what can be reported relative to purchase, installation, and 

maintenance costs? In contrast, if the proposed rule relieves industry of testing or other costs, please 

provide any known estimate of costs.]

The proposed new compliance method will reduce the overall cost and time of the joint 

certification process. Most current aircraft designs accommodate the JAR compliance 

method, which is currently more stringent than the FAR. Therefore the costs for new type

design certification should be minimal. Supplemental and Amended type designs may 

have to include additional agent or more complex distribution systems to be able to show 

compliance. FAR/JAR 25.855(h)(2) requires certification of extinguishing agent 

dissipation rates by flight test. Since gaseous extinguishing systems typically can only be 

flight tested after the first airplane installation is completed due to the effects of 

compartment leakage, the costs of meeting the more stringent point concentration 

standard are significant if the design must be changed and re-tested at the end of a 

development program. These last-minute changes are costly for all projects, whether for 

New, Amended or Supplemental type designs.

17. - If advisory or interpretive material is to be submitted, document the advisory or 

interpretive guidelines. If disagreement exists, document the disagreement.

The Draft Advisory Circular contains the proposed harmonized method of compliance 

with the provisions of 14 CFR Part 25 §§ 25.851, 25.855 and 25.857 of the Federal 

Aviation Regulations (FAR) related to the built-in fire suppression systems when required

for cargo compartments for transport category airplanes. This material provides 

definitions of the applicable cargo compartments, locations where gaseous extinguishing 

agent concentrations should be measured, and what the minimum concentration should be 

at different locations within the compartment. Methods for certifying agent 

concentrations with loaded compartments, for evaluating data anomalies, for the effect of 

airplane maneuvering on test data and brief excursions below the required lower limits 

are also provided.

18 - Does the HWG want to review the draft Notice of Availability of Proposed Advisory 

Circular prior to publication in the Federal Register?
No Notice is required since only advisory material is proposed. However, it has been the 

policy of the Transport Airplane Directorate to provide a Notice of Availability of 

Proposed Advisory Circular (AC) and request for comments prior to issuing advisory 

material. Therefore, the HWG would like to review any draft notice prior to publication 

in the Federal Register.

19 – In light of the information provided in this report, does the HWG consider that the 

“Fast Track” process is appropriate for this rulemaking project, or is the project too 

complex or controversial for the Fast Track Process. Explain. [A negative answer to this 

question will prompt the FAA to pull the project out of the Fast Track process and forward the issues to the 

FAA’s Rulemaking Management Council for consideration as a “significant” project.]

This project is recommended for the Fast Track process as it is believed that sufficient 

corroborating test material is currently available. FAA has a draft AC prepared which 

incorporates the intended guidance.