2 Prior to issuance of the Generic Model Airplane Type Certificate, it must be shown by design or analysis that adequate fire protection has been provided to the cockpit voice and flight data recorders, windows, primary flight controls (unless it can be shown that a fire could not cause jamming or loss of control), and other systems and equipment within the compartment that is required for safe flight and landing. If protective covers are used, they must be constructed of materials that meet the flame penetration resistance requirements of 14 CFR part 25, appendix F, part III [Amendment 25-60].
e. Reference. The address for ordering the latest revision of advisory circulars and other referenced documents listed below can be found in the Appendix to this AC.
AC 25-9A; Smoke Detection, Penetration, and Evacuation Tests and Related Flight Manual Emergency Procedures.
38. SECTION 25.857 - CARGO COMPARTMENT CLASSIFICATION.
a. Rule Text.
(a) Class A. A Class A cargo or baggage compartment is one in which-
(1) The presence of a fire would be easily discovered by a crewmember while at his station; and
(2) Each part of the compartment is easily accessible in flight.
(b) Class B. A Class B cargo or baggage compartment is one in which-
(1) There is sufficient access in flight to enable a crewmember to effectively reach any part of the compartment with the contents of a hand fire extinguisher;
(2) When the access provisions are being used, no hazardous quantity of smoke, flames, or extinguishing agent, will enter any compartment occupied by the crew or passengers;
(3) There is a separate approved smoke detector or fire detector system to give warning at the pilot or flight engineer station.
(c) Class C. A Class C cargo or baggage compartment is one not meeting the requirements for either a Class A or B compartment but in which-
(1) There is a separate approved smoke detector or fire detector system to give warning at the pilot or flight engineer station;
(2) There is an approved built-in fire-extinguishing or suppression system controllable from the cockpit;
(3) There are means to exclude hazardous quantities of smoke, flames, or extinguishing agent, from any compartment occupied by the crew or passengers;
(4) There are means to control ventilation and drafts within the compartment so that the extinguishing agent used can control any fire that may start within the compartment.
(d) [Reserved] 101
(e) Class E. A Class E cargo compartment is one on airplanes used only for the carriage of cargo and in which-
(1) (Reserved)
(2) There is a separate approved smoke or fire detector system to give warning at the pilot or flight engineer station;
(3) There are means to shut off the ventilating airflow to, or within, the compartment, and the controls for these means are accessible to the flight crew in the crew compartment;
(4) There are means to exclude hazardous quantities of smoke, flames, or noxious gases, from the flight crew compartment; and
(5) The required crew emergency exits are accessible under any cargo loading condition.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-32, 37 FR 3972, Feb. 24, 1972; Amdt. 25-60, 51 FR 18243, May 16, 1986; Amdt. 25- 93, 63 FR 8048, Feb. 17, 1998]
b. Intent of Rule. This rule provides the standards for the various classes of transport category airplane cargo compartments. It does not cover closets and stowage compartments (See § 25.787). Cargo compartment liner standards and required flight tests to demonstrate compliance are addressed in § 25.855.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in section 4b.383 of the CAR were carried over essentially unchanged to § 25.857 of 14 CFR.
(1) Amendment 25-32 (February 24, 1972) moved the liner requirements for Classes B through E to § 25.855.
(2) Amendment 25-60 (May 16, 1086) limited the volume of Class D compartments to a maximum of 1,000 cubic feet.
(3) Amendment 25-93 (February 17, 1998) revised paragraph (c)(2) to add reference to suppression systems as well as extinguishing systems, and eliminated reference to Class D compartments and reserved paragraph (d). Also see the explanation under § 25.855, Amendment
25-93.
(4) Harmonization. This regulation is the subject of a Federal Aviation Regulation/Joint Aviation Requirement (FAR/JAR) harmonization effort under the Aviation Rulemaking Advisory Committee (ARAC). The ARAC working group has provided the FAA with a fully harmonized draft notice of proposed rulemaking (NPRM) and an accompanying draft proposed advisory circular (AC) for regulatory evaluation. The NPRM and the AC provide the criteria for corrective action(s) that, if implemented, would be acceptable to the FAA for showing compliance with the airworthiness directive AD 93-07-15, or any new "combi" designs for Class B or the new proposed Class F cargo compartments. The NPRM proposes to revise §§ 25.855 and 25.857, and the proposed AC provides one means but not the only means of 102
compliance. Should an applicant not desire to comply with the requirements for Class B or class F compartments as stipulated above, then the main deck cargo compartments should comply with requirements for a Class C compartment as defined in current §§ 25.855 and 25.857.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preambles of this rule and the following information.
(1) Main Deck Cargo Compartment Fire Protection Certification Procedures. The following policy is extracted from an FAA letter dated June 6, 1997, and addresses requirements for “combi” airplanes. The letter is in response to a request from an applicant for information regarding certification of “combi” airplanes. The FAA refers to airplanes that can carry both passengers and cargo on the main deck as "combi's." The guidance is based on proposed rulemaking and advisory material being developed through the ARAC process.
(a) Information was requested concerning Federal Aviation Administration (FAA) requirements for certification of “combi” airplanes. The minimum design requirements for issuance of a Type Certificate for large transport airplanes are identified in 14 CFR part 25. The FAA was specifically asked to identify the criteria against which the FAA would evaluate the main deck fire protection features for FAA certification.
(b) The passenger and cargo compartments are separated by a partition that is either fixed or movable to accommodate various passenger/cargo combinations. Some “combi’s” can also accommodate all passenger or all cargo configurations. In most cases, the main deck cargo compartments on these airplanes are identified as Class B cargo compartments, which meet the fire protection requirements specified in § 25.857(b). Class B cargo compartments rely on manual firefighting as the primary method of controlling fires.
(c) In 1987, a South African Airways 747-200 “combi” crashed in the Indian Ocean following a fire in it’s main deck Class B cargo compartment. Following the investigation, the FAA concluded that manual firefighting in large Class B cargo compartments was not effective, and that the certification requirements identified in § 25.857(b) were inadequate. As a result, the FAA issued Airworthiness Directive (AD) 93-07-15, which required operators of existing large “combi” airplanes manufactured by Boeing or McDonnell Douglas to make significant modifications to their airplanes and operations. Operators were offered four options: (1) convert the Class B cargo compartment to Class C, (2) carry all cargo in the Class B cargo compartment in containers that meet the requirements for Class C cargo compartments,
(3) use fire containment covers or containers for all main deck cargo, along with other airplane and operational changes, or (4) incorporate a 90 minute duration fire suppression system, along with other airplane and operational changes.
(d) To address new “combi” designs, the FAA, through the Aviation Rulemaking Advisory Committee (ARAC) process, is proposing a revision to §§ 25.855 and 25.857 which would require Class B cargo compartments to be small enough that a crewmember with a hand held fire extinguisher can extinguish a fire anywhere within the compartment without entering it.
The FAA is also proposing a new cargo compartment classification, Class F. The proposed 103
Class F compartment would not be size-limited, and would require incorporation of a means to extinguish or control the fire without the need for a crewmember to enter the compartment. This includes not reaching in to move something in order to have full access to the fire extinguisher.
(e) The FAA has identified the criteria against which the FAA would evaluate main deck fire protection features on new “combi’s.” Although AD 93-07-15 provides an adequate level of safety for existing airplanes, the FAA recommends that all new “combi’s” meet the intent of the proposed changes to §§ 25.855 and 25.857. In addition, the effectiveness of the third and fourth options of AD 93-07-15 depends heavily on the FAA-monitored procedures, maintenance, and training at individual airlines, whereas the proposed part 25 changes rely on the airplane design, rather than airline operations. The FAA recognizes that the limited size of the proposed Class B cargo compartment would not meet operational needs. The FAA recommends that the main deck cargo compartment on the “combi” meet either the requirements for Class C cargo compartments identified in §§ 25.855 and 25.857, or the proposed requirements for Class F cargo compartments. The FAA and the ARAC are proposing that Class F cargo compartments meet the general cargo compartment requirements of § 25.855, and the following:
1 A Class F cargo compartment must have a liner that is separate from, but may be attached to, the airplane structure, unless it can be shown that other means for containing the fire and protecting critical systems and structure are provided.
2 The ceiling and sidewall panels of the liner in the Class F cargo compartment, if required, must meet the test requirements of part 25, Appendix F, part III, or other FAA-approved equivalent methods. This includes windows and window shades/covers in combi airplanes.
3 A means to extinguish or control the fire in the Class F cargo compartment, without requiring a crewmember to enter the compartment, must be provided.
4 A means to prevent hazardous amounts of smoke, flames, or suppression agent in the Class F cargo compartment from entering any occupied compartment must be provided.
5 A separate, FAA-approved smoke or fire detector system to alert the pilot or flight engineer station in the event of a fire must be provided.
(2) Class A Cargo Compartments: The following policy is extracted from an FAA memorandum dated February 8, 1996, to provide FAA policy regarding certification of passenger airplanes converted to all-cargo Class A or unclassified cargo compartment configurations.
(a) The FAA Transport Airplane Directorate has become aware of a number of transport category airplanes that have been reconfigured as all-cargo airplanes with cargo 104
compartments classified as Class A, or with the cargo compartment classification not addressed at all.
(b) An FAA memorandum , dated September 13, 1988, states that " . . . the agency policy has always been, and still is, that cargo compartments larger than that stated in Order 8110.27A(5)(b) are to be classified as Class B through E, whichever is applicable, and that operators comply with all requirements relative to each class." The aforementioned order describes the Class A compartment as " . . . small open compartments used for storage of crew luggage and located in the cockpit area where a fire can be easily discovered by a crewmember."
The order goes on to state that: "During the 74/75 Airworthiness Review, it was mentioned that full cabins or other large cargo compartments were presented for approval under Class A category, and that these compartments were consistently rejected on the basis that their volume was outside the intent of the Class A category where a fire must be rapidly detected and extinguished. Since the Class A compartment has no liner, large cargo areas have been considered to be outside the intent of the Class A category. It was recommended to limit the volume to 200 cubic feet."
(c) Advisory Circular (AC) 25-18, issued January 6, 1994, Transport Category Airplanes Modified for Cargo Service, addresses this subject. In the AC, Class A compartments are defined as follows:
1 "A Class A compartment is one that is located so close to the station of a crewmember that the crewmember would discover the presence of a fire immediately. In addition, each part of the compartment is easily accessible so that the crewmember could quickly extinguish a fire with a portable fire extinguisher. A Class A compartment is not required to have a liner.
2 "Typically, a Class A compartment is a small open compartment in the cockpit area used for storage of crew luggage. A Class A compartment is not, however, limited to such use; it may be located in the passenger cabin and used for other purposes provided it is close to a crewmember's station. Typically, the crewmember would be a member of the flightcrew; however, the compartment could be located adjacent to the station of any other crewmember.
3 "Because a Class A compartment does not have a liner, it is absolutely essential that the compartment be small and located close enough to a crewmember that any fire that might occur could be discovered and extinguished immediately. Without a liner to contain it, an undetected or uncontrolled fire could quickly become catastrophic by burning out of the compartment and spreading throughout the airplane. There is no specific limit on the volume;
however, all portions of the compartment must be virtually within arms length of the crewmember in order for any fire to be detected immediately and extinguished in a timely manner. Although there may be some exceptions, such as a 'U-Shaped' compartment for example, a Class A compartment greater than 50 cubic feet in volume would not typically have the accessibility required by § 25.857(a)(2) for fighting a fire."
(d) Advisory Circular 25-17, Transport Airplane Cabin Interiors Crashworthiness Handbook, dated July 15, 1991, or latest revision, notes that a Class A compartment was envisioned as a small, open compartment located in the cockpit area.
(e) It is clear from reviewing the above policy, and noting the chronology, that the intent of Class A compartments is not consistent with the conversion of an entire passenger cabin to a cargo compartment and identifying it as Class A. A number of issues support this view. In order to exit the airplane in the event of an uncontrollable fire, the only path may be through the fire zone. Access to emergency exits often does not exist with the compartment fully loaded.
Further, there are no means to protect the flightcrew from the effects of toxic gasses that can be generated in a smoldering fire. In cargo compartments classified Class B through Class E, the cargo and crew areas are separated and certification tests are conducted to ensure that no hazardous quantities of smoke or fumes will penetrate occupied areas, including the cockpit. In addition, other factors that are frequently not addressed in these modifications are: lack of a cargo restraint system, compartment liners, and a second emergency exit.
(f) The FAA has determined, for the reasons discussed above, that it is inappropriate to classify full cabin or other large areas as Class A compartments. For future certification projects (whether new, amended, or supplemental), the above guidance must be considered.
(3) Class E Cargo Compartments. The following policy is extracted from an FAA memorandum dated March 21, 1991, in response to a request for guidance on compliance relating to the installation of a Class E cargo compartment.
(a) Smoke detection capability must be demonstrated in any flight condition contemplated by the operator. This usually means a flight test must be performed at the maximum contemplated cabin altitude.
(b) Smoke penetration from Class E compartment into cockpit tests must be conducted starting in a cruise configuration and continuing into a descent to sea level landing. If any other procedures, such as attempting to suppress the fire by going to higher altitudes, involve other operating altitudes, these must also be addressed.
(c) An Airplane Flight Manual (AFM) supplement is needed which addresses crew action following smoke annunciation, i.e., crew shuts off ventilating air to the cargo compartment, dons oxygen equipment, and proceeds to the nearest adequate airport.
(d) The protective breathing equipment requirement in § 25.1439(a) must be addressed.
(4) Access to Class E Cargo Compartments. The following policy is extracted from an FAA letter dated July 3, 1990, in response to a request for guidance on compliance on the carriage of dangerous goods, and the need for access, in Class E compartments.
(a) The International Civil Aviation Organization regulations for hazardous goods carried in Class E compartments require adequate access to these goods. Section 25.857 of 14 CFR does not preclude access to Class E compartments in flight. Sections 25.851(a)(3) and
121.309(c)(2) require that one hand fire extinguisher must be provided for use in each Class E cargo compartment that is accessible to crewmembers in flight.
(b) Although part 25 does not require in-flight access to Class E cargo compartments, in-flight access to the compartment can be accommodated with proper design if operational requirements result in the carriage of hazardous goods in a Class E compartment.
(5) Freighter Aircraft with Accessible Class E Compartment. The following is extracted from an issue paper dated March 10, 1995, titled “Accessible Class E Cargo Compartment.”
(a) The following applies to certification of a freighter aircraft with an accessible Class E Cargo Compartment, which would allow the operator to carry hazardous material. The following would allow the crew and "persons" access to the entire cargo compartment.
(b) Access by one cargo handler will be allowed during flight to a Class E cargo compartment carrying hazardous material provided that one Portable Breathing Equipment (PBE) meeting TSO C-116 is available in the flight deck. The cargo handler in the Class E cargo compartment must carry the portable oxygen at all times while in the cargo compartment. A placard must state that the portable oxygen must be carried at all times. In addition, there must be a readily detectable means to alert the cargo handler to don oxygen equipment and/or return to the flight deck. Further, two Halon fire extinguishers of adequate size must be installed near the cargo compartment entrance with procedures for their use. Finally, there must be a means to prohibit smoking. Compliance with the above will meet §§ 25.855(e)(1), (e)(2), and
25.857(e)(4), taking into consideration the opening caused by a person exiting the cargo compartment.
(c) The applicant should show by test or by analysis that with the access door open in flight the positive ventilation with only one pack operating is capable of excluding smoke, flames, or noxious gasses in compliance with § 25.857(e)(4). In addition, the additional fire extinguisher that was kept on the flight deck was required to be a 16-pound Halon extinguisher to comply with § 121.309(c)(2).
e. References. The addresses for ordering the latest revision of referenced documents listed below can be found in the Appendix to this AC.
Advisory Circular, 25-XX, Cargo Compartment Fire Extinguishing or Suppression Systems, date TBD.
Advisory Circular, 25-XX, Class B and F Cargo Compartments, date TBD.
Two methods of determining the leakage rate for Class D compartments that have been approved for certification are contained in:
Appendix I of CAA Technical Development Report No. 146, Evaluation of Flight Fire Protection Means for Inaccessible Aircraft Baggage Compartments, dated June 1951, and FAA Technical Center Report DOT/FAA/CT-83/1, Analysis of Dissipation of Gaseous Extinguisher Agents in Ventilated Compartments, dated May 1983.
39. SECTION 25.858 - CARGO OR BAGGAGE COMPARTMENT SMOKE OR FIRE DETECTION SYSTEMS.
a. Rule Text.
If certification with cargo or baggage compartment smoke or fire detection provisions is requested, the following must be met for each cargo or baggage compartment with those provisions:
(a) The detection system must provide a visual indication to the flight crew within one minute after the start of a fire.
(b) The system must be capable of detecting a fire at a temperature significantly below that at which the structural integrity of the airplane is substantially decreased.
(c) There must be means to allow the crew to check in flight, the functioning of each fire detector circuit.
(d) The effectiveness of the detection system must be shown for all approved operating configurations and conditions.
[Amdt. 25-54, 45 FR 60173, Sep. 11, 1980; Amdt. 25-93 63 FR 8032, Feb. 17, 1998]
b. Intent of Rule. This rule provides minimum design and certification requirements for cargo or baggage compartment fire or smoke detection systems. This rule is intended to provide a standard that a fire be detected and indicated to the crew in less than one minute after inception.
c. Background. This section was added to part 25 of the Code of Federal Regulations (14 CFR) with Amendment 25-54. Prior to Amendment 25-54, a detection limit of no more than five minutes was established by policy since there was no regulatory reference to detection time.
Section 25.858(d) requires detection testing in any configuration proposed by the applicant, including depressurized flight. The cognizant ACO may certify minor changes by analysis of similarities to previously certified configurations, laboratory test, or ground test.
(1) Amendment 25-93 (February 17, 1998) revised the section heading and introductory paragraph to add reference to baggage compartments and smoke detection systems.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.
(1) Smoke Detection Certification Testing. The following policy is extracted from an FAA memorandum dated June 18, 1997, which was developed in response to inquiries regarding smoke quantities to certify smoke detection systems in cargo compartments. The memo was used to distribute video guidance to help clarify smoke quantities specified in Advisory Circular (AC) 25-9A.
(a) Section 25.858(a) requires that a cargo compartment fire detection system provide a visual indication to the flightcrew within one minute after the start of a fire. AC 25-9A, section 10, provides guidelines for the conduct of certification tests related to smoke detection. The AC states that systems which provide a warning within one minute from the start of smoke generation are considered to be in compliance with the requirements of § 25.858 for cargo compartments.
Paragraph 10.b. states that the objective of the smoke detection test is “to demonstrate that the smoke detection system installation will detect a smoldering fire producing a small amount of smoke.”
(b) In February 1997, FAA/Industry meetings were held to discuss how manufacturers and operators intended to support the part 25 and 121 rule changes requiring fire detection and suppression systems to be installed in existing Class D cargo compartments. During the meeting, Industry expressed concern that a large number of conversions were going to be made and several Aircraft Certification Offices (ACO’s) would be impacted. Industry was concerned that the smoke detection standards used by the ACO’s varied and requested the FAA’s effort to standardize the test criteria used to satisfy § 25.858.
(c) In response to this request, the FAA held a standardization workshop at the FAA Technical Center in Atlantic City, NJ, during April 1997. ACO personnel and designated engineering representatives (DER’s) attended to discuss smoke generation and quantities, and other certification requirements relevant to cargo compartments requiring both detection and suppression systems.
(d) During the standardization workshop, the Technical Center provided a demonstration of a typical smoke quantity from a smoldering fire by igniting rags inside a suitcase.
There was a consensus agreement among the ACO members present that this suitcase demonstration generated an appropriate quantity of smoke for a one minute detection system. It was agreed that a video of the burning suitcase should be distributed to the ACO’s as an aid to visually demonstrate the amount of smoke that is representative of smoke from a smoldering fire as is mentioned in AC 25-9A. This video is considered visual guidance demonstrating a typical amount of smoke from a smoldering fire. The amount of smoke demonstrated in this video helps to clarify the objective of paragraph 10.b. in AC 25-9A.
(e) Copies of the video mentioned above are available through the FAA William J.
Hughes Technical Center. Refer to the Appendix of this AC for the mailing address.
(f) Additional items of discussion at the workshop included the following:
1 The tests conducted at the FAA Technical Center have shown that some materials that are routinely carried in cargo compartments burn very quickly with open flames 109
and little smoke. It was shown that a fire internal to a suitcase can rupture an aerosol can (containing butane, propane, or isobutane) contained therein and cause the liner to be breached.
Once the liner is breached, ventilation control and ability to maintain adequate Halon concentration will be lost. It is inappropriate to rely on detection systems that depend on copious quantities of smoke prior to detection. A fire does not know what volume compartment it is in.
A smoldering fire will generate the same levels of smoke regardless of the compartment size and should be detected within the required time to detection (one minute or five minutes as applicable) in any compartment. The solution to larger compartments may be an increased number of detectors, increased sensitivity of detectors, different type of detectors (fanned or ionic), or infrared detectors.
2 All of the current smoke detection limits and guidance have been subjective and based on previous certification practices. The FAA Technical Center's planned test program includes defining fire hazards, the amount of heat generated, and the typical quantity (in more objective terms) of smoke generated, associated with typical cargo fire hazards. The suitcase video is intended to provide clearer guidance until the Technical Center test program is complete. It is a continuing step toward standardizing the approach to smoke detection testing until the FAA determines usable, objective criteria.
(2) Certification Testing for Smoke Detection. The following policy is extracted from an FAA memorandum dated February 11, 1993, in response to an inquiry regarding certification of smoke detection systems in the cargo compartments of transport category airplanes, and provides guidance for determining detection times for these systems.
(a) Advisory Circular (AC) 25-9 and AC 25-17, differ in the guidance provided for time to detection for certification testing. AC 25-9 states in paragraph 7.e.(3) that "smoke detection should occur within one minute after the start of smoke generation." AC 25-17 states in paragraph 671.b.(6) that "An acceptable detection time for smoke detectors is 5 minutes. Use the smoke quantity and location criteria of AC 25-9, 'Smoke Detection, Penetration, and Evacuation Tests, and Related Flight Manual Emergency Procedures,' for showing that the smoke detection system detects a fire in satisfactory time. The time for fire detection systems was changed to one minute by Amendment 25-54 in § 25.858."
(b) The guidance contained in AC 25-9 reflects the detection times required in Amendment 25-54, which added § 25.858. This section established a higher standard of safety than previously existed for transport category airplanes, and applies to airplanes which have Amendment 25-54 in their certification basis. When an applicant applies for an amended or supplemental type certificate to convert a passenger configuration to a cargo configuration on an older airplane whose certification basis predates Amendment 25-54, the allowable maximum detection time is not specifically stated in 14 CFR. The five minute detection time, which is not mentioned in AC 25-9, was established in an FAA letter in 1965, and has been the accepted maximum detection time requirement until § 25.858 became effective on September 11, 1980.
(c) If an applicant applies for an amended or supplemental type certificate and the certification basis for the airplane predates Amendment 25-54, there is no regulatory basis for 110
requiring a detection time of one minute. The applicant should be encouraged to meet the later amendment, or to make detection within one minute a design goal, but it would be inappropriate to require that the applicant comply with § 25.858.
(d) Two additional points should be made regarding wording in regulations that address fire detection systems. When the terms "fire detector" or "fire detection system" are used, this also encompasses smoke detectors and smoke detection systems. A review of the preamble to Amendment 25-54 reveals that the rule is intended to address systems which detect fires, and smoke detection systems were included. Also, questions are frequently asked regarding the expression that detection must occur "within one minute after the start of a fire."
As noted in AC 25-9, time to detection is measured "after the start of smoke generation."
Therefore, detection time is defined as the elapsed time from when the smoke generator is activated (switched to the mode which actively generates smoke) to when detection occurs (annunciation of smoke detection to the flight crew).
(3) Smoke Detection Certification Testing. The following policy is extracted from two FAA letters dated December 3 and December 15, 1992. The letters were in response to a request for approval of five items discussed in a meeting between the FAA and an applicant on November 6, 1992, all related to "Smoke Detection Testing Methodology/Procedures For Compliance To § 25.858."
(a) The five items below were discussed individually. It was noted prior to responding that the positions provided in the letter related to demonstration of compliance with the provisions of § 25.858, as promulgated by Amendment 25-54, and were not intended to provide guidance as to methods to be used for certification of an airplane which does not have Amendment 25-54 in its certification basis. In addition, the responses provided were not intended to be all inclusive. Other methods of demonstrating compliance could also be acceptable.
(b) The first proposal related to a specific fuel load (using tobacco as the fuel), tamping, and lighting procedure to be used for generating smoke to show compliance with the FAA requirements. The procedure and the tobacco weights were proposed to meet the requirements in a large compartment such as in a large transport category all cargo airplane.
There were two charges (basket sizes) proposed. These two charges should be acceptable for all large transport category airplane cargo compartments. The FAA reserves the option to stipulate smaller fuel loads when finding compliance in small compartments.
(c) The second proposal discussed the use of a smoke deflector hat, which is required to provide a more realistic smoke propagation pattern than a direct smoke exhaust directed toward the crown of the compartment. The FAA had seen no evidence that a direct smoke stack exhaust provided a representative smoke pattern. It was stated that the deflector hat would continue to be required in future tests using a tobacco generator.
(d) The third proposal requested approval of continuous smoke generation until detection, and allowed "averaging" the detection times to give a one minute overall average for 111
all positions tested, with maximum time not to exceed 110 seconds at any location.
Section 25.858 states that detection must occur within one minute after the start of a fire. When § 25.858 was proposed, several commenters stated that the one minute detection time was too stringent, especially in light of the existing policy (5 minutes to detection). It was the opinion of the commenters that the technology was not available to enable the airplane manufacturers to meet the one minute requirement. The preamble to the final rule, issued as part of Amendment 25-54, noted that the technology was available or would be available when new airplanes affected by the rule were certificated. Subsequently, a number of airplanes have shown compliance with the one minute rule, indicating that the promulgators of the rule were correct in their assessment. The technology is available, and the FAA could not arbitrarily change that requirement to allow a fire to go undetected for 110 seconds in some locations in the cargo compartment. Such a finding would not be in accordance with the rule as issued. A rule change to allow longer detection times in special cases, such as for very large cargo compartments on all-cargo airplanes, would be required.
(e) The fourth proposal dealt with a means to reduce the number of locations at which smoke would be generated within the compartment to diminish the costs associated with flight testing new cargo compartment configurations. The proposal stated that smoke detection locations would be representative of high, low, and normal detection locations as documented in the applicant's tests. The certification locations were to be randomly selected from a population of representative locations. The number of representative test locations must be at least twice the number of required certification test locations and they must be available for FAA review.
Typically, laboratory and ground testing determine the worst locations in each part of the compartment. The random selection of flight test locations should be acceptable provided the whole population of ground test times is already compliant with the rule. The FAA determined that this approach was acceptable for demonstrating compliance with § 25.858, and also for testing on the applicant's airplane.
(f) The fifth proposal discussed the "Statistical Procedure and Methodology" for demonstrating compliance with § 25.858. The proposal to use an average detection time for all locations, with no tested location having a detection time exceeding 110 seconds, was not acceptable to the FAA. However, it was recognized that smoke testing is not a perfectly repeatable process, and testing at any one location may yield varying detection times with multiple tests. Previous certification tests have proceeded as follows: If the first test at a given location results in a detection time of greater than 60 seconds, the applicant must repeat the test two more times; if the resulting average of the three tests at the given location is 60 seconds or less, the given location is a “Pass;” if the resulting average of the three tests at the given location is greater than 60 seconds, the given location and the fire detection system are both “Failed” and require a redesign of the system.
(g) Two additional points were raised by the applicant. In the FAA response to the second proposal, paragraph (c) above, regarding the use of a smoke deflector hat on the smoke generator, the FAA noted that "...we will continue to require the deflector hat on future tests."
The applicant was concerned that this statement could lead to a misunderstanding regarding the use of the deflector hat on previous tests. The FAA had commented in previous correspondence 112