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 d ue to an on

- board fire, or to the

use of built

- in systems intended to combat them, FAR/JAR 25.851(b) requires that built

in fire extinguishers be installed so as to be non

- hazardous to airplane occupants who are likely to be exposed to them, that the disch arge 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

i ndicated 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 buil t

- 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) Bu ilt

- 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 c ompartment 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/capa bility, 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 appl ication 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, inclu ding 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 occup ants 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 Categ ory 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 Cla ss 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 percentby 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 averag ing of sensor data to show compliance. The FAA has also accepted in the past the use of CO 2 decay tests to determine the cargo compartment leakage in flight, with the Halon concentration determined analytically. This also resulted in approval of an avera ge 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 ext inguishing 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 130 1 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 r eignites, 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 lette rs (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 whil e 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, date d 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 conductingflight 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

demonstrat ions 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 su itability 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. Additio nal 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 wo rding 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 Ma terial 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 capabilit y 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 saf ety 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 stru cture, 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 in tent 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 isrequired by the FAR (e.g., gen eral 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 propos ed 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 w hy 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 con sidered, 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 ti me 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 ope rators, 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 ag ent 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 su bstantive 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 mate rial 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 adviso ry 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 w ill 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 Air craft 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 beli eved 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 disch arged 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 Certifi cation 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 o n 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 commitme nts 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 o f 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 o ther 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) o f 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 cont rast, 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 design s 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 d istribution 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 instal lation 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 a re 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 D raft 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 car go 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 diffe rent 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 p rovided.

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 th e 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 Feder al 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 F ast 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.