1 Purpose.
2 Applicability.
3 Cancellation.
10/11 / 18 AC 20 - 144A 1 PURPOSE .
1.1 This AC provides acceptable means for showing compliance with the requirements of 14 CFR 2X.1301, Function and installation, with regard to fire extinguishing or suppression systems that contain electrical firing cartridge components. Airplanes having to c omply with part 23 rules using a mendment 23 - 64, effective August 30, 2017, must show compliance with § 23.2505 , Function and installation .
1.2 This AC also includes the various aspects that should be considered by applicants seeking approval from the Federal Aviation Administration (FAA) of fire extinguishing or suppression systems that contain electrical firing cartr idge components manufactured under a production certificate (PC), components to be approved under the part manufacturer approval (PMA) process, or design changes to components originally approved by either method. Since each environment and installation ma y differ, the applicant should select those portions of this document necessary to show compliance and coordinate it with the responsible FAA engineer, inspector, or their designee. This AC does not address other firex components or the complete aircraft s ystem installation.
There may be airframe installation requirements and boundary conditions that should be met prior to installation approval.
2 APPLICABILITY .
The guidance in this AC is for applicant s requesting a PC or PMA, or a new , or amended, or supplem ental type certificate (STC) . This guidance is also for aircraft manufacturers, modifiers, foreign regulatory authorities, FAA air craft type certification engineers , FAA manufacturing inspectors, and the Administrator’s designees.
2.1 The material in this AC i s neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations. The FAA will consider other means of demonstrating compl iance that an applicant may elect to present. While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations. If, however, we become aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation or design changes as a basis for finding compliance.
2.2 Th e material in this AC does not change or create any additional regulatory requirements, nor does it authorize changes in , or permit deviations from, existing regulatory requirements.
3 CANCELLATION.
This AC cancels AC 20 - 144, Recommended Method for FAA Approval of Airc raft Fire Extinguishing System Components , dated September 22, 2000.
4 Summary of Changes.
6 Definitions.
10/11 / 18 AC 20 - 144A 5.3 Orders.
The following FAA orders are related to the guidance in this AC. The latest version of each order at the time of publi cation of this AC is identified below. If any order is revised after publication of this AC, you should refer to the latest version for guidance, which can be downloaded from the Internet at http://www.faa.gov/regulations_policies/orders_notices/ .
Order 8110.42D, Parts Manufacturer Approval Procedures , dated March 21, 2014.
Order 8120.16A, Suspected Unapproved Parts Program , dated June 3, 2016.
Order 8120.22A, Production Approval Proced ures, dated January 11, 2016.
5.4 Other Documents.
The following documents are related to this AC. If any of these documents are revised after publication of this AC, you should refer to the latest version.
M IL - DTL - 23659F NOT 1, Initiators, Electrical, General Design Specifications for , dated March 18, 2015 , ASSIST (DoD Specs and Standards) .
AIAA - S - 113A - 2016/A1 - 2018 , Criteria for E xplosive Systems and Devices on Space and Launch Vehicles , dated 2018 , https://aiaa.org .
M IL - C - 22284A(1) NOT 1 (AS), Revision A, Notice 1, Container, Aircraft Fire Extinguishing System, Bromotrifluoromethane, CF3BR , dated September 18, 1996 , ASSIST (DoD Specs and Standards) .
RTCA/DO - 160G, Change 1, Environmental Conditions and Test Procedures for Airborne Equipment , dated December 16, 2014 , https://www.rtca.org/ .
SAE AIR5060 A, Electronic Engine Control Design Guide for Electromagnetic Environmental Effects , dated August 11 , 2011 , https://www.sae.org/ .
6 DEFINITIONS.
For the purpose of this document, the following definitions apply: 6.1 All - Fire and No - Fire Reliability C ondi tions.
“ All - fire” and “no - fire” are minima and maxima conditions for different cartridges under specific operating conditions. Refer to MIL - DTL - 23659F.
6.2 Backshell.
Metal shell connecting circuit shields or overbraid to an electrical connector.
6.3 Burst D isc.
D iaphragm that ruptures to allow extinguishing agent to escape.
7 Scope.
10/11 / 18 AC 20 - 144A 6.4 Cartridge.
Device used for discharging pressurized extinguishing agent. These are sometimes referred to as firing cartridges and initiators. These components meet definition of critical com pone nt under FAA Order 8110.42D, a ppendix K .
6.5 Discharge Head.
Device that houses cartridges and interfaces between the pressure vessel and the agent distribution system. This is sometimes referred to as the cartridge body or header assembly.
6.6 Firex.
Any fire ext inguishing or suppression system that consists of the extinguishing agent container (vessel) and all attached components.
6.7 Pressure I ndicator.
Device to indicate pressure or status of pressure vessel.
6.8 Production Approval Holder (PAH).
The holder of a produc tion certificate, parts manufacturer approval, or technical standard order authorization who controls the design and quality of a product or part.
7 SCOPE.
7.1 A fire extinguishing or suppression (firex) system is required by subpart E of part s 23, 25, 27, and 2 9 , among other p art 2X provisions (for example, §§ 2X.851, 2X.854, 2X.855, 2X.857, 2X.901, 2X.1195, 2X.1197, 2X .1199 , 2X.1201, 2X.1301, and 2X .1309). A firex system is composed of many components that are critical for the proper operation of the system whe n installed in an aircraft. One such component may be an e lectrical firing cartridge component. While there are no specific regulatory requirements on the design, production, or testing of an e lectrical firing cartridge, § 2X .901(b)(2) requires that compon ents of the installation be constructed, arranged, and installed to ensure their continued safe operation between normal inspections and ove rhauls. Additionally, § 2X .1301(a)(1) and (4) requires that each item of installed equipment must be of a kind and d esign appropriate to its intended function and operate properly when installed . This AC does not address other firex components or the complete aircraft system installation. There may be airframe installation requirements and boundary conditions that shoul d be met prior to installation approval.
7.2 The applicant should evaluate the firex system and establish minimum reliability standards for the components of the system so the overall system can meet the requirements of subparts E and F of part s 23, 25, 27, an d 29 . In accordance with § 2X.1529 , the maintenance instructions should also be provided. These instructions should include required service after discharge.
8 Firex System Functional Overview.
9 Firex Cartridge Performance Parameters Overview.
10/11 / 18 AC 20 - 144A 7.3 The applicant should design and qualify components to meet specific operating performance, service life, and reliability requirements of the firex system established at the time of type design approval.
7.4 The FAA recommends that PAH and PMA applicants demonstrate that their candidate components meet or exceed these criteria. This document describes the c ritical parameters involved with the design, production, and testing of the electrical firing cartridge component.
8 FIREX SYSTEM FUNCTIO NAL OVERVIEW.
8.1 There are generally three , cartridge - activated , firex system s onboard commercial aircraft. These systems pr ovide fire extinguishment or suppression for engines, auxiliary power units (APU s ) , and cargo compartments . The extinguishing agent is contained in a pressurized vessel that is seale d with a precision burst disc. A discharge head, containing a cartridge an d strainer , is at tached to the pressure vessel.
8.2 When a fire is detected , an electrical pulse to the firing cartridge activates the firex system (activation may be automatic or commanded by a flightcrew member). The aircraft electrical system supplies the p ulse, and the agent is discharged into the fire zone through a distribution system of piping and nozzles.
8.3 Most firex systems are designed to us e a firing cartridge. In some types, w hen the firex cartridge activates, it produces a controlled shock wave that fractures the burst disc on the pressurized container, allowing the agent to escape.
8.4 In other t ypes, the firex cartridge , upon activation , either propels a slug into the burst disc and discharges the agent , or supplies a pressurizing force to drive a pist on that, in turn , moves a cutter knife that pierces the burst disc and allows the agent to disperse.
8.5 The opening in the burst disc is dependent on the application — high - rate discharge for engine or APU, or a combination of high - rated and flow - metered discha rge for cargo compartments. In either case, the opening of the burst disc diaphragm should meet critica l performance characteristics. A proper size opening should ensure the correct flow rate of agent to the desired destination.
8.6 A firex system may use a sy stem of diverter valves , components of the flow metering, and filters to control where the agent travels for some cargo compartment applications.
9 FIREX CARTRIDGE PERFORMANCE PARAMET ERS OVERVIEW .
9.1 General.
A firex cartridge is an explosive component of an ai rcraft firex system. The applicant is responsible for ensuring that the design and qualification of firex cartridges meet the specific operating performance, service life, and reliability requirements of aircraft firex system designs. This section discusse s parameters for the design, production, testing, 10/11 / 18 AC 20 - 144A and approval process. To comply with § 2X.1301, the applicant should verify that these parameters are appropriate for the installation and perform analysis and qualificati on testing to validate the cartridg e. These analyses and tests are discussed in paragraphs 9.4 , 9.5 , 9.7 , and 9.9.2 of this AC .
9.2 Design Parameter s.
9.2.1 Physical Parameters.
Physica l parameters include all information related to how the cartridge interfaces with the aircraft firex system. These include, but are not limited to: Length dimensions (e.g., threads, output cup, overall, connector).
Diameter dimensions (e.g., threads, outpu t cup).
Concentricity of dimensions.
Tolerances.
Thread size.
Thread type.
Electrical connector specification.
Mounting features (e.g., relationship of cartridge output cup to pressure vessel burst disc).
9.2.2 Electrical Parameters.
Electrical parameters includ e the electrical signal required to initiate the cartridge in a proper and reliable manner. Of equal importance are the electrical requirements that ensure the cartridge will not inadvertently fire. The cartridge electrical parameters should be compatible with the applicable aircraft electrical system requirements, limitations, and tolerances. The following is a list of electrical parameters: 9.2.2.1 Minimum Firing Current .
The applicant should establish the minimum firing current required to initiate the cartridg e in a reliable manner. This is typically expressed with a current level and time duration such as 3.5 - ampere pulse for 10 to 50 milliseconds.
9.2.2.2 Firing Circuit .
Each type of cartridge has a different firing circuit. The type and number of circuits are relat ed to the connector specified for the particular aircraft.
The identification and proper orientation of the pins on the cartridge are critical for correct functioning of the firex system. The circuit diagram identifies each pin on the cartridge, typically by a letter or number. In Values may depend on the installation requirements.
10/11 / 18 AC 20 - 144A addition, the applicant should specify the circuit resistance, typically 1.0 ohm for each unit.
9.2.2.3 No - Fire Current .
The no - fire current is the maximum current at which the device will not fire or degrade, typically 1 amp or 1 watt f or five minutes.
9.2.2.4 Electrostatic Discharge .
The cartridge should not fire when exposed to an electrostatic discharge pulse. An electrostatic discharge is typically 25,000 volts from a 500 picofarad capacitor through a 5,000 ohm resistor shorted pin(s) - to - ca se.
9.2.2.5 Electromagnetic Interference (EMI).
Applicants should use RTCA/DO - 160G as a standard and should determine limitations on the aircraft. The cartridge should not fire when exposed to various electromagnetic fields. Radar and communication systems general ly produce these types of fields. The applicant should establish EMI protection criteria based on aircraft system EMI limitations.
9.2.2.6 Insulation Resistance/Dielectric Withstanding Voltage.
The applicant should use insulation resistance of typically 100 megoh ms at 500 volts DC to prevent the loss of a fire pulse due to internal shorting or arcing.
9.2.2.7 Dielectric Strength .
The cartridge should typically have a dielectric strength of 1000 volts AC root mean square ( RMS ) shorted pin(s) - to - case, and the leakage rate should not be greater than 0.1 milliamps for 60 seconds.
9.2.3 Functional Parameters.
Upon initiation, the cartridge should provide sufficient energy to open the burst disc effectively, but not enough energy to cause a failure of the firex system or aircraft.
9.2.3.1 In stalled Air Gap.
The installed air gap is the distance between the end of the cartridge and the surface of the ruptured state of the disc. The applicant should establish the installed air gap with the approved burst disc(s) , considering all system installa tion variables and tolerances, and accounting for repair limits for the bottle burst disc assembly, to determine the minimum and maximum gap conditions. The applicant should use the minimum and maximum gap for system level testing.
9.2.3.2 Burst Disc Opening.
The applicant should identify the opening size of the burst disc for the applicable installation, which is a critical performance characteristic, and 10/11 / 18 AC 20 - 144A evaluate the proper size opening to ensure the adequate flow rate of agent to the desired destination. The siz e of the required opening may be different for an engine or APU versus cargo compartment installations.
The applicant should establish burst disc opening with the pyrotechnic charge and electrical energy specifications at their minimum tolerance and the mi nimum and maximum temperatures established for the system. This disc opening should be equal to or greater than the minimum flow area of the discharge head. It is essential that the applicant establish an adequate margin of safety.
9.2.4 Environmental Parameters .
According to § 2X.1301, the cartridge should function properly for its intended function , which means it should function normally after exposure to all the environmental conditions it is expected to operate in. The applicant should consider the additiona l environmental parameters in RTCA/DO - 160G, or equivalent specifications.
Examples include: High temperature (200 ºF) .
Low temperature ( - 65 ºF).
Temperature shock/humidity/altitude cycling.
Vibration.
Shock.
Drop test (6 feet).
Drop test (40 feet).
Values can depend on the installation requirements.
The cartridge does not have to function properly after a 40 - foot drop but should remain safe, i.e., not explode or burst.
10/11 / 18 AC 20 - 144A 9.3 C artridge Design .
Figure 1 below shows an example of a firex cartridge.
Figure 1 . Cross - S ection View of a Typical Firex Cartridge.
9.3.1 Backshell.
9.3.1.1 The backshell is typically a stainless steel housing with pins imbedded in a high - pressure hermetic seal. The pins provide the electrical connections from the external wiring or connector to the bridgewire. The environmental and glass seals are critical in providing a high - pressure hermetic seal before and after firi ng. They provide: Pressure and shock barrier between the explosive output and the electrical connections.
Hermetic moisture seal to protect the explosive charges.
Mechanical retention of the pins.
Electrical isolation of the pins.
10/11 / 18 AC 20 - 144A 9.3.1.2 Cracked or poor seals, du e to design or quality issues, can cause failures because the header pins could be explosively dislodged from the cartridge, resulting in agent leakage t hrough the cartridge backshell. Also, cracked or poor seals can allow moisture to infiltrate and degrad e the explosive charges during the environment exposure cycles of aircraft op eration. This will degrade performance as well as the effective service life of the cartridge. The applicant should define the method of verifying the integrity of the seal (typic ally using a helium leak test).
9.3.2 Bridgewire.
The bridgewire initiates the detonation by heating the ignition charg e to its ignition temperature. The specific bridgewire size and material should be selected to meet the required all - fire and no - fire reliabili ty. See paragraphs 9.2.2.1 and 9.2.2.3 of this AC for the definitions of minimum firing current and no - fire current.
9.3.3 Explosive Charges.
The typical cartridge contains a minimum of two types of explo sive charges : an ignition charge and an output charge. These charges initiate sequentially in the cartridge to generate the required energy output to ruptur e the firex system burst disc. The bridgewire initiates the cartridge by heating the ignition charge to its ignition temperature.
9.3.3.1 Ignition Charge .
The ignition temperature and thermal conductivity characteristics of the ignition charge have a significant effect on the all - fire and no - fire reliability and performance of the cartridge.
9.3.3.2 Output Charge .
When initiated, the output charge provides the energy focused to open the burst disc effectively without causing other damage to the firex system or aircraft.
9.3.4 Part Labeling.
To comply with § 2X .1301, firing cartridge components should be labeled. The labeling s hould include the applicable “manufactured on” date or “life - limited date.” 9.3.5 Shorting Springs and Shunts.
Firing cartridge components are often shipped using a shorting spring or shunt mounted on the cartridge electrical connector. There have been instances where shunts were left installed inadvertently on the cartridge connector during installation. This effectively disables th e firex system. When these cases were detected , the FAA released airworthiness directives (ADs) to correct the condition. To comply with § 2X.1301 and prevent future ADs , firing cartridge components should be designed to ensure that cartridges may not be installed with such devices in place. Alternatively, where this is impractical , the device should be distinctively marked with instru ctions to ensure correct installation.
10/11 / 18 AC 20 - 144A 9.4 Cartridge Validation.
To validate compliance to § 2X.1301, the all - fire and no - fire condition tests may consist of firing a group or groups of cartridges at various current levels and noting the performance characteri stics of the cartridge. The applicant should establish s pecific quantities of specimen s for testing to be statistically significant and provide the desired confidence levels. The current levels should be statistically selected and the results analyzed to p rovide no - fire and all - fire current ratings at various required reliability and confidence levels (0.99 reliability at 95 percent confidence ) with reference to the engineering design test s chedule in MIL - DTL - 23659F.
9.5 Basic Qualification.
The FAA recommend s that the applicant qualify each cartridge design to meet and address the items listed in the engineering design test schedule in MIL - DTL - 23659F , plus an additional test sequence to ensure open disc performance ( pursuant to paragraph 9.2.3.2 of this AC ) at high and low temperature extremes . The test should use a representative bottle and burst disc charged to the minimum allowable pressure using 7 bottle/disc test units per high and low temperature condition for a total of 14 fir ings .
( S ee M IL - DTL - 23659F. ) 9.6 Pre - P roduction Design and Quality Control.
The FAA will review the applicant’s quality system to ensure the inspection system that is required by part 21 is in place. The applicant should ensure that the cartridge design, develo pment, qualified baseline, and quality aspects are maintained throughout the production life cycle and meet the requirements in §§ 21.1, 21.137, 21.303, and Orders 8110.42D and 8120.22 A .
9.6.1 Manufacturing Processes.
The applicant should use a documented and co ntrolled system to ensure that cartridge components are manufactured or procured from a qualified source that provides closed - loop controls to ensure material acceptability . One example of the importance of this documented and controlled system is to ensur e the quality of the seal in the cartridge body (header assembly), which is a critical component. Poorly manufactured seals may result in failure, as the header pins could be explosively dislodged from the cartridge, causing agent to leak through the cartr idge or backshell, or allowing air or moisture contamination of the pyrotechnic mixture. The manufacturing processes that the applicant should address are identified and described below: 9.6.1.1 Bonding Assemblies .
Bonding of the assemblies is critical to ensure t he cartridge meets all electrical requirements. Failure to achieve complete and proper bonded assemblies may cause failure in dielectric strength, insulation resistance, or electrostatic discharge capability. This may result in inadvertent firing of the ca rtridge during electrical surges from sources such as lightning, or failure to fire if the cartridge is electrically shorted. Bonding processes include, but are not limited to: 10/11 / 18 AC 20 - 144A Proper mix ratio definition.
Cure temperature and time definition.
Cleanliness of bonded surfaces definition.
Coverage of bonded surfaces definition.
Bridgewire material selection.
9.6.1.2 Bridgewire Welding .
Bridgewire welding is critical to ensure that the proper electrical energy is transfer red to the explosive material , which is a chieved through the bridgewire. Typically, the bridgewire is resistance - welded to the header pins and is process - sensitive. Poor bridgewire welds may result in the cartridge failing to fire as the bridge circuit may open during normal temperature cycling, shock, and vibration. Welding parameters include, but are not limited to: Length of the bridgewire.
Location of the bridgewire weld on the header pins.
Strength of the bridgewire welds.
Resistance values.
Bridgewire material.
9.6.1.3 Powder Preparation.
The applicant sho uld use documented procedures to control c ritical processes . These procedures should ensure handling safety , ingredient consistenc y , and consistency from production lot to production lot. Each powder blend should be characterized and tested for performance and accepted prior to use in production cartridges. Typically, testing includes caloric content, particle size, thermal analy sis, and performance analysis.
Steps include , but are not limited to: Use of controlled and approved procedures.
Acceptance testin g of powder prior to use in production cartridges.
Documentation and approval of raw materials.
Storing and handling.
Verification of moisture content.
10/11 / 18 AC 20 - 144A 9.6.1.4 Powder Loading.
Powder loading is critical to the functional per formance of the cartridge.
The applicant should verify m oisture content, hygroscopic capability, and volatility of the powder to ensure proper ignitio n and output of the explosive. Proper density of the powder should be achieved to ensure all - fire and no - fire cap ability. Failure to ensure moistu re, volatility content, and proper pack density will typically result in failure to fire or inadve rtent firing from stray voltages. Processes include, but are not limited to , control of the : Process environment.
Consolidation force of the explosive into th e cartridge.
Length of time the consolidation force is applied.
Accuracy of the powder quantity to be loaded.
9.6.1.5 Hermetic Sealing.
Environmentally sealing the cartridge by a hermetic seal ensure s the cartridge meets the prescribed life requirements. Failure t o achieve a hermetic seal will reduce service life as the explosive material degrades through normal environment conditions. The applicant should verify the - 6 integrity by testing 100 percent for leakage (e.g., 1 x 10 standard cubic centimeter per sec ond o f helium at one atmosphere) .
9.6.2 The FAA or its delegates will not allow deviation to the approved manufacturing procedures at any level of assembly, unless the applicant evaluates the deviation under an FAA - approved process.
9.7 Quality Verification .
To comply wi th § 2X .1301 , the cartridge design or changes to cartridge design, manufacture , or processes of cartridge testing should encompass the entire spectrum of criteria from cartridge design, development, qualification, and production and storage prior to instal lation. The performance elements of the cartridge at the firex system level that are typically used to develop the test and validation methods are: 9.7.1 Design Development.
During development, the cartridge design requirements are dictated by the firex system p erformance requirements. The applicant can correlate these results with other non - system - level function tests (e.g., agent flow, function time, and environments) and use the results to determine how to test the cartridge based on the engineering design tes t s chedule in MIL - DTL - 23659F, and the addition of disc opening performance tests in paragraph 9.5 of this AC.
10/11 / 18 AC 20 - 144A 9.7.2 Design Change Control.
The applicant should have a process for design changes in a method acceptable to the FAA. The applicant should validate all design changes to the firex system performance and reliability requirements.
9.7.3 Design Qualification and Validation.
System qualification testing should ensure that the cartridge: Performs the required functions at the system lev el.
Can effectively open the burst disc, allowing correct agent flow under all operating and expected environmental conditions.
Does not cause any peripheral degradation of the firex system as the result of the explosive event occurring.
9.7.4 Testing.
9.7.4.1 During ca rtridge qualification and validation, the applicant should perform system level tests to demonstrate the capability of a cartridge design to meet the burst disc rupture requirements. A typical number of tests at the system level is seven according to MIL - C - 22284A. Cartridge qualification and validation also involve non - system - level testing where key design elements are evaluated ( see the engineering design test s chedule in MIL - DTL - 23659F). This combined test series establishes baseline reliabil ity and perfo rmance parameters.
9.7.4.2 After design validation, the applicant should correlate the results with other non - system - level function tests to develop criteria for suitable production lot acceptance tests. Such testing can effectively indicate manufacturing process control issues in a validated design. However, the applicant should not use the results of the testing to demonstrate the suitability of a new design for a given system. Using non - system - level test methods to demonstrate similar performance of a new design to a qualified design does not validate the suitability of a new design to work properly in an installed firex system. The applicant should substantiate the u se of non - system - level tests and analysis to show equivalence as installed on the actual firex sy stem.
9.7.4.3 The applicant should verify proper storage and handling procedures are in place to ensure that firing cartridges function properly in support of §§ 2X.1301 and 2X .1309 requirements.
10/11 / 18 AC 20 - 144A 9.7.5 Production Lot Acceptance Testing.
Cartridge sample lot acceptance t esting is a means of assessing the manufacturing process to ensure nothing has changed that might have a ffected cartridge performance.
After cartridge qualification, the applicant should develop test methods and criteria to ensure production cartridges con form to the performance require ments of the qualified design. This demonstrates that the production cartridges have not changed with respect to the qualified design . Production lot acceptance tests should include, for example: Bridgewire resistance on 100 percent of the lot.
Dielectric strength on 100 percent of the lot.
Insulation resistance on 100 percent of the lot.
Leakage on 100 percent of the lot.
Radiographic on 100 percent of the lot.
Electrostatic discharge on 100 percent of the lot (if applicable) .
No - fire on a lot sample.
All - fire on a lot sample.
Functional performance on a lot sample.
9.8 Service Life Issues.
9.8.1 The firex sy stem is a safety system that is exposed to repeated cycles of tempera ture, altitude, and vibration. This system remains dormant, u ntil it is needed, and then should perform flawlessly. C ompromis ing on the long - term quality when approving new, modifi ed, or replacement cartridges could result in catastrophic loss of the airplane. For example, cracked seals and poor welds can be patched with potting to pass helium leak tests dur ing production lot acceptance. However, this low - quality fix may not survive the entire rated service life. Repeated cycles of temperature and altitude can force moistu re into the explosive charges. As previously discussed, this can cause cart ridge failure resulting in non - actuation of the firex system, which would compromise safety of the airplane. Section 2X.1301 requires that the systems function properly when installed.
9.8.2 To comply with § 2X.1301, the applicant s hould identify the method to validate the proposed service life of the cartridge. Accelerated life testing should reference AIAA S - 113A - 2016, section 5.5.1 , Age Surveillance of Explosive Components , or equivalent, except for the following: Note: Prior to initial approval, the applicant should complete this validation and evaluate the aircraft installation environment with respect to the service life test plan to ensure compatibility with the proposed service life of the cartridge.
1. An additional performance discha rge sequence for the non - system - level function testing identified in paragraph 9.7.4.2 of this AC should be conducted in accordance with AIAA S - 113A - 2016 .
10/11 / 18 AC 20 - 144A 2. When performing accelerated age testing as listed in AIAA S - 113A - 2016, section 5.5.1 , Age Surveillanc e of Explosive Components , establish the temperature and time using the method referenced in the National Institute of Standards and Technology, NIST/SEMATECH e - handbook of Statistical Methods: http://www.itl.nist.gov/div898/handbook/apr/section1/apr151.htm .
9.8.3 Determining accelerated age test temperature and time using in - service temperature and time: Most aircraft installations do not have a uniform environmental temperature wher e the cartridges are installed. Some cargo installations are in a location that are environmentally controlled when the aircraft is in operation, but see temperature variations when the aircraft is not in use. Other cartridges are installed outside the pre ssure vessel of the aircraft in the same compartments as engine bleed ducting; these see large variations in temperature between ground operation and in - flight conditions (some may be as high as 160 ºF and as low as - 80 ºF).
The number of collisions that c an cause reactions increases exponentially with temperature. This can sometimes double with an increase of as little as 10 ºC. I t may not be correct to use the average or mean installed temperature when determining the installed temperature used in the acc elerated age testing calculation . U sing a lower average temperature would ignore the detrimental effects that occurs at even relatively short periods of time at the highest temperatures . U sing the maximum installed temperature would conservatively cover th e in - service environment but would not take credit for the time spent at the lower temperatures. The applicant must propose a method found acceptable to the FAA to determine the usage temperature to be used in the accelerated temperature life testing.
9.9 Fina l Approval Process.
9.9.1 Qualification Document Package.
The applicant should include the following: An overall certification plan.
Detailed drawings on the proposed item.
Manufacturing and quality procedures and processes.
Engineering change orders for the pro posed item and configuration control.
Statement of differences between the proposed item and the baseline item.
Approved plan to address the testing specified in the engineering design test s chedule in MIL - DTL - 23659F.
Data/report showing successful complet ion of all proposed component level tests on the proposed item.
Approved qualification test plan on the applicant ’ s and PAH ’s items.
Data/report showing successful completion of approved qualification test plan.
Data/report showing approved system - level te st.
10/11 / 18 AC 20 - 144A Data/report showing successful completion of all system - level tests in the system - level test plan.
Approved production functional test methods to be used on both items with an explanation of the pass/fail criteria.
Approved service life test plan.
Data /report showing successful completion of the service life testing according to the approved life test plan.
Approved production quality screening plan (lot acceptance).
9.9.2 Final Qualification.
The qualification is performed by conducting adequate analyses and testing to verify that the components will function properly when installed in the installation environment with the required reliability. With respect to appropriate testing in RTCA/DO - 160G, qualification provides an accepted means for testing components in various environments. Qualification can be done to support an application for a type certificate (TC) , an amended TC , or a n STC . The applicant should submit a qualification test plan to the FAA or its authorized designee. The results of the qualificati on should be provided for approval in a qualification test report to the FAA or its designee. Additionally, applicants may produce after - market components with a PMA.
9.9.2.1 There are three ways to receive a PMA. They are identicality, identicality by licensing a greement, and by test and computation. Sections 21.301 through 21.320 and Order 8110.42D describe the responsibilities of the FAA aircraft certification offices (ACOs) and manufacturing inspection district offices ( MIDOs) and applicants, and the process fo r approving replacement and modification articles for installation on type - certificated products when issuing a PMA. The associated procedures for the FAA (MIDO) and manufacturing personnel are in Order 8120.22A. Applicant guidance is in AC 21.303 - 4. When applying these procedures to firex cartridges, t he applicant should address the following items: 9.9.2.1.1 PMA Approval by Identicality.
Engineering drawings and specifications of the proposed cartridge should contain adequate detailed information to define the cart ridge assembly and its components accurately, item by item, to show identicality to approved parts. The applicant must obtain FAA approval for any significant differences with the original approved cartridges under the test and computation method. Examples of significant differences are charge material changes, loading changes, process changes, changes in supplier or manufacturer, and physical configuration differences.
10/11 / 18 AC 20 - 144A 9.9.2.1.2 PMA Approval by Licensing Agreement.
According to § 21.303(a)(4), if the applicant obtai ns the design of the electrical firing cartridge by a licensing agreement, the applicant must provide evidence of that agreement.
9.9.2.1.3 PMA Approval by Test and Computation.
Test and computation requires a PMA applicant to conduct analyses and tests necessary to show they produce an electrical firing cartridge that meets the performance and reliability of the production version. The test method is to fire the cartridge in charged bottles under operational conditions. RTCA DO - 160 (latest revision) provides guidanc e for component testing in the appropriate environment. Typically, the firex system - level tests are coordinated with the FAA. They are performed during the development and qualification of a new design and should establish system performance of replacement parts.
9.9.2.2 For parts determined to be critical or life - limited, the FAA may require the applicant to perform inspections and tests and submit the results to the FAA. These test results are necessary to show airworthiness of parts produced in conformity with t he proposed design to obtain design approval. If the application is based on identicality, no testing is normally required. If the application is based on test and computation, or an STC , the applicant should submit both design and qualification test resul ts.
9.9.2.3 The applicant should address all sections of this AC in a certification plan per part 21, subpart G, and obtain FAA approval for the certification plan prior to beginning qualification activities.
9.9.2.4 The applicant should address any aspect that might degr ade: Safety.
Performance.
Soundness of mechanical design.
Resistance to environment.
Service life.
9.9.2.5 The FAA considers all cartridges in air craft f ire e xtinguishing and s uppression s ystem s as critical components and therefore requires the applicant to define performance testing requirements and conduct such tests.
10/11 / 18 AC 20 - 144A 9.9.2.6 The FAA considers all subsequent changes to the design under the definition provided in § 21.93. The applicant should not ship any parts that are of any major change configuration prior to receivin g FAA approval of that change. The applicant may need to seek guidance as to whether its proposed change should be considered major or minor. Parts shipped prior to FAA approval of any major change may be subject to the suspected unapproved parts reporting requirements of Order 8120.16A.
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