AS6826 Powerplant Fire Test Standard

Aircraft powerplant fire testing has historically relied on a combination of FAA advisory material, legacy engineering reports, SAE standards, ISO guidance and certification-project precedent. These sources established a strong technical foundation, but they also permitted differences in burner configuration, flame calibration, test-article representation, operating boundary conditions and acceptance criteria.

AS6826 was issued by SAE International in April 2025 to provide a more consistent and prescriptive framework for demonstrating compliance with powerplant installation and propulsion-system component fire-protection requirements. Its development followed a March 2018 FAA request for SAE International to create industry standards supplementing FAA AC 20-135 Change 1. The work was undertaken by the SAE A-22 Fire Protection and Flammability Testing Committee with participation from industry and aviation certification authorities.

The standard defines fire-test methodologies, burner requirements, temperature and heat-transfer calibration procedures, representative test conditions, boundary-condition assessment and component-specific pass/fail criteria. Its purpose is to reduce unnecessary variation between certification programmes and improve the quality, repeatability and defensibility of fire-test evidence.

AS6826 does not replace applicable airworthiness regulations or remove the need for certification-authority agreement. Applicants remain responsible for establishing the applicable requirements, proposed means of compliance, test configurations and acceptance criteria for each certification project. Early coordination is particularly important where an installation includes unusual geometry, non-conventional propulsion, hybrid-electric systems, novel materials or project-specific boundary conditions.

AS6826 is an SAE Aerospace Standard providing guidance and acceptable fire-test methods for powerplant and auxiliary power unit components and installations. It addresses the demonstration of fire-resistant and fireproof performance through controlled exposure to a calibrated standard flame.

The standard covers:

• Fire-test planning and reporting.

• Representative test articles and installation conditions.

• Acceptable liquid-fuel burners.

• Flame-temperature calibration.

• Flame heat-transfer-rate calibration.

• Test boundary conditions.

• Fire-intended functions.

• Component-specific pass/fail criteria.

• Residual flames, outgassing and backside ignition.

• Firewalls, nacelle hardware, fluid systems, controls and fire-detection equipment.

AS6826 is intended to:

• Harmonise powerplant fire-testing practices.

• Reduce unnecessary variation between test facilities.

• Establish repeatable burner-calibration methods.

• Improve consistency in boundary-condition selection.

• Define clearer pass/fail criteria.

• Generate stronger certification evidence.

• Supplement FAA AC 20-135 Change 1.

• Support coordination between applicants, suppliers, test laboratories and certification authorities.

AS6826 applies to certification fire testing. It should not be treated as a generic material flammability standard or as a substitute for system safety assessment.

A fire test can produce a technically misleading result if the burner is incorrectly calibrated, the test article is unrepresentative or the applied operating conditions are less severe than the installed aircraft environment. AS6826 reduces this risk by requiring a structured justification of the test article, flame, setup, critical exposure location, boundary conditions and acceptance criteria.

The standard provides methods intended to support demonstration of applicable powerplant fire-protection requirements. However, the applicant must still identify the governing regulations and obtain agreement on the proposed means of compliance.

Compliance with AS6826 should therefore be viewed as part of a certification strategy, not as a stand-alone certificate of regulatory compliance.

Consistent calibration methods improve comparability between tests. AS6826 requires pre-test flame-temperature and heat-transfer-rate calibration, controlled burner settings during the test and post-test heat-transfer-rate validation before the burner is shut down.

These controls reduce uncertainty over whether a test article experienced the required fire severity.

The standard focuses on fire-intended functions. A component may be required to contain fire, prevent hazardous leakage, remain attached, carry load, close a shut-off path, preserve drainage, maintain an alarm or prevent flame penetration.

The relevant function must be defined before testing because the required function determines both the test conditions and the pass/fail criteria.

AS6826 draws upon, supplements or affects a wider body of fire-test documentation, including:

• FAA AC 20-135 Change 1, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria.

• FAA Powerplant Engineering Report No. 3A, Standard Fire Test Apparatus and Procedure.

• ISO 2685, Aircraft environmental test procedure for airborne equipment, resistance to fire in designated fire zones.

• SAE AIR1377, Fire Test Equipment for Flexible Hose and Tube Assemblies.

• SAE AS1055, covering fire testing of flexible hose, tube assemblies, coils, fittings and similar system components.

• SAE AS4273, covering fire testing of fluid-handling components.

• SAE AS5127/2, covering aerospace firewall sealant flame-penetration testing.

• SAE AS8028, covering powerplant fire-detection instruments.

• Applicable FAA regulations, EASA Certification Specifications and supporting acceptable means of compliance.

AS6826 states that its text takes precedence over referenced material where a conflict exists within its defined application. It does not supersede applicable laws or regulations.

The standard is prescriptive, but test programmes remain installation-specific. Tailoring may be required for:

• Aircraft category.

• Engine or APU installation.

• Designated fire-zone geometry.

• Test-article size and complexity.

• Critical burner orientation.

• Flame impingement location.

• Fluid type, temperature, pressure and flow.

• Vibration and mechanical loading.

• Differential pressure.

• Backside airflow.

• Rotational speed.

• Commanded or controlled functions.

• Ground and flight operating conditions.

• Engine-running and engine-shutdown phases.

• Novel propulsion or energy-storage systems.

Tailoring must not be used to reduce test severity without an adequate engineering justification.

The applicant should obtain early agreement on:

• Applicable regulations.

• Fire-resistant or fireproof classification.

• Proposed means of compliance.

• Test-article representativeness.

• Critical test conditions.

• Burner orientation.

• Boundary-condition values.

• Pass/fail criteria.

• Test deviations.

• Required witnessing and conformity arrangements.

Novel configurations may require issue papers, Certification Review Items or equivalent authority coordination.

• Identify applicable regulations and certification requirements.

• Determine whether the design requires fire-resistant or fireproof performance.

• Define every fire-intended function.

• Identify critical flame-application locations.

• Assess ground and flight operating envelopes.

• Determine worst-case boundary conditions.

• Agree the means of compliance with the certification authority.

• Prepare the fire-test plan and compliance matrix.

• Manufacture or select representative test articles.

• Confirm configuration and conformity status.

• Replicate production materials, joints, seals, fasteners and interfaces.

• Install representative heat paths and heat sinks.

• Configure operational pressures, flows, loads and functions.

• Install calibrated instrumentation.

• Verify test-facility safety controls.

• Confirm video coverage of flame-side and backside behaviour.

• Inspect and record the test configuration.

• Warm up the burner.

• Complete pre-test temperature calibration.

• Complete pre-test heat-transfer-rate calibration.

• Apply the defined boundary conditions.

• Begin video and data recording.

• Move the burner into the calibrated test position.

• Conduct the required exposure.

• Maintain or transition boundary conditions as defined.

• Monitor leakage, flame penetration, backside ignition and fire-intended functions.

• Observe the test article after burner withdrawal.

• Complete post-test heat-transfer-rate validation before shutting down the burner.

• Assess the fire-intended functions.

• Review flame penetration and burn-through.

• Review leakage and fluid release.

• Confirm load retention where applicable.

• Examine backside ignition.

• Record residual flame size, location and duration.

• Examine outgassing, damage and deformation.

• Review all deviations from the approved procedure.

• Complete the fire-test report.

• Include photographs and video references.

• Attach calibration and validation data.

• Document test-article conformity.

• Confirm adherence to boundary conditions.

• Record pass/fail conclusions against each criterion.

• Close deviations with the certification authority.

• Update the certification compliance matrix.

AS6826 defines the standard flame as having:

• A minimum flame temperature of 2,000°F or 1,093°C.

• A minimum heat-transfer rate of 4,500 Btu/h or 1,319 W when measured using the prescribed continuous-flow copper-tube apparatus.

The flame-temperature requirement and the heat-transfer-rate requirement are separate calibration controls. Both must be satisfied before testing.

The standard requires:

• A seven-thermocouple rake.

• Exposed-junction Type K thermocouples.

• A minimum recording rate of 0.5 Hz.

• A minimum three-minute calibration period.

• An individual average temperature of 2,000°F ±150°F for each thermocouple.

• A minimum rake average temperature of 2,000°F across the five inner thermocouples.

Individual thermocouple averages above 2,150°F may be accepted as conservative, but they represent a more severe condition than the standard intends.

The heat-transfer device uses a controlled water flow through a copper tube exposed to the flame. The calculated heat-transfer rate is based on water flow, density, specific heat capacity and measured inlet-to-outlet temperature rise.

Key controls include:

• Water flow of 1.00 US gal/min ±0.05 US gal/min.

• A minimum three-minute recording period.

• A minimum sample rate of 0.5 Hz.

• A pre-test average heat-transfer rate of at least 4,500 Btu/h.

• No adjustment to burner settings after successful calibration.

Post-test validation confirms that burner performance did not deteriorate during testing.

• If the copper tube is cleaned before validation, the average must remain at or above 4,500 Btu/h.

• If cleaning is impossible without shutting down the burner, the permitted validation threshold is 4,100 Btu/h.

• Failure to achieve the applicable post-test threshold can invalidate the fire test and require repetition.

For a fireproof test, the powerplant or APU is generally represented as running during the first five minutes. Shutdown or windmilling conditions may then apply during the remaining ten minutes, depending on the installation and approved test plan.

Each listed boundary condition must be assessed for applicability:

• Induced vibration.

• Mechanical or structural loading.

• Differential pressure.

• Backside airflow.

• Commanded or controlled function.

• Fluid pressure.

• Fluid flow.

• Fluid temperature.

• Fluid-reservoir quantity.

• Component rotational speed.

• Test fluid.

The worst-case value for each applicable condition may occur at a different aircraft operating point. The test matrix must therefore demonstrate that every applicable worst-case condition is represented or conservatively enveloped.

Pass/fail criteria must be defined for the specific component and its fire-intended functions. Typical criteria include:

• No burn-through.

• No unacceptable flame penetration.

• No backside ignition.

• Continued load capability where applicable.

• Leakage within approved limits.

• Residual flames within acceptable limits.

• Maintenance of the fire-intended function.

• No external flammable-fluid leakage during exposure.

• Continued operation of required fire-intended functions.

• Maintenance of applicable pressure and flow conditions.

• No failure of mounting provisions that could create an additional hazard.

Immediately after burner retraction, no leakage greater than weepage insufficient to form a drop is permitted for applicable flammable-fluid conveyance products.

A fire-resistant shut-off valve may be required to close following the initial five-minute exposure without external leakage.

A fireproof shut-off valve may additionally be required to remain closed and pressurised during a further ten minutes of flame exposure.

The detector system must perform the defined fire-intended function during exposure. AS6826 distinguishes this installation-level function from the broader equipment qualification tests contained in AS8028.

Residual flames may be acceptable where they:

• Do not compromise the fire-intended function.

• Do not violate another pass/fail criterion.

• Are significantly smaller than the burner flame.

• Do not propagate.

• Show an overall reduction in intensity.

• Self-extinguish within two minutes after burner removal.

Residual flames must be recorded by duration, size, quantity and video. System-level implications may require certification-authority review.

Incorrect burner calibration, damaged thermocouples, unsuitable instrumentation or poor burner positioning can invalidate a test.

A failed pre-test calibration, unacceptable post-test validation or uncontrolled deviation may require the complete test to be repeated.

Large nacelle structures, firewalls, complex component installations and representative three-dimensional rigs can require substantial tooling, instrumentation and test-facility preparation.

A test may be severe in one parameter but non-representative in another. Combining individually conservative values can also create an unrealistic configuration that changes the failure mechanism.

Weak configuration records, incomplete boundary-condition justification or unclear pass/fail criteria can make technically successful testing difficult to accept for certification.

Late authority engagement can expose disagreement over the means of compliance after hardware, tooling and test plans have already been committed.

State exactly what the component must do during and after exposure. Avoid generic wording such as “must survive the test”.

The test article should represent production materials, geometry, joints, penetrations, seals, fasteners, heat paths and installation constraints.

Record why each AS6826 boundary condition is applicable or not applicable. Do not omit a condition without justification.

Assess the full normal operating ground and flight envelope. “Typical operation” is not necessarily the certification worst case.

Do not change burner fuel flow, airflow, geometry or settings after successful calibration and before post-test validation.

Thermal deformation, rig movement or vibration must not change the calibrated distance between the burner and the critical test location.

Video coverage should detect flame-side behaviour, backside ignition, leakage, deformation, outgassing and residual flames.

Record test-article identity, drawings, build standard, materials, production processes, deviations and conformity status.

Pass/fail criteria should be measurable, observable and approved before the burner is lit.

Early engagement reduces the risk of repeating tests because the authority disagrees with the configuration, boundary conditions or means of compliance.

A complete AS6826 compliance package may include:

• Fire Protection Compliance Plan.

• Certification Programme.

• Means-of-Compliance Matrix.

• Fire-Test Plan.

• Fire-Test Specification.

• Boundary-Condition Assessment.

• Test-Article Representativeness Assessment.

• Test Procedure.

• Conformity Records.

• Instrumentation and Calibration Records.

• Burner Temperature Calibration Records.

• Heat-Transfer-Rate Calibration Records.

• Post-Test Validation Records.

• Photographic and Video Records.

• Test Deviation Records.

• Fire-Test Report.

• Certification Compliance Matrix.

• Hazard Assessments.

• System Safety Assessments.

• Certification-Authority Correspondence.

Applicable regulatory and certification requirements are mapped to objective evidence.

The burner meets the required temperature and heat-transfer-rate conditions before testing and the applicable validation threshold after testing.

The test article satisfies the defined requirements for burn-through, flame penetration, leakage, ignition, load retention and residual flames.

Every defined fire-intended function is maintained for the required duration or transitions to an approved safe state.

The test report links the test article, drawings, configuration, boundary conditions, procedure, instrumentation, data and acceptance criteria.

The applicant obtains acceptance of the fire-test evidence through the applicable certification process.

Resonate supports the identification of applicable requirements, certification assumptions and proposed means of compliance.

Resonate provides engineering interpretation of AS6826, FAA guidance, EASA requirements and related fire-test standards.

Resonate supports assessment of aircraft operating envelopes and identification of representative or worst-case test conditions.

Support can include:

• Test strategy.

• Test-article definition.

• Critical flame-location assessment.

• Test matrix development.

• Instrumentation requirements.

• Test procedure development.

• Pass/fail criteria.

• Risk and contingency planning.

Resonate can support the interpretation and application of temperature calibration, heat-transfer-rate calibration and post-test validation requirements.

Support may include the preparation or independent review of:

• Compliance plans.

• Test plans.

• Test specifications.

• Test procedures.

• Boundary-condition assessments.

• Test reports.

• Compliance matrices.

Independent technical review can identify gaps in representativeness, calibration, test severity, traceability and certification evidence before testing begins.

Resonate can support technical engagement with applicants, aircraft manufacturers, engine manufacturers, test laboratories and certification authorities. Authority acceptance remains the responsibility of the applicant and the relevant certification authority.

AS6826 is an SAE Aerospace Standard providing fire-test methods, calibration requirements, boundary-condition guidance and pass/fail criteria for powerplant and propulsion-system components and installations.

AS6826 was issued in April 2025.

It was created to supplement FAA AC 20-135 Change 1 and reduce variation in powerplant fire-test methods, calibration, boundary conditions and acceptance criteria.

No. AS6826 significantly supplements the advisory circular. The applicable regulations, certification basis and agreed means of compliance still govern the project.

The standard flame has a minimum temperature of 2,000°F or 1,093°C and a minimum calibrated heat-transfer rate of 4,500 Btu/h or 1,319 W.

No. Under AS6826, 4,500 Btu/h is the minimum heat-transfer rate measured using the prescribed copper-tube apparatus. It should not be described as a heat-flux density value.

Fire-resistant testing requires a minimum five-minute flame exposure. Fireproof testing requires a minimum 15-minute flame exposure. The applicable fire-intended functions and pass/fail criteria must also be satisfied.

Where applicable, yes. The applicant must assess vibration, load, pressure, airflow, fluid conditions, function, rotational speed and other installation-specific boundary conditions.

Induced vibration is normally required unless the test article meets the defined exclusion criteria or the certification authority accepts an alternative justification.

Pre-test flame-temperature and heat-transfer-rate calibration is required. Burner settings must then remain unchanged through the test and post-test validation.

Yes. Heat-transfer-rate validation must be completed before the burner is shut down. The applicable minimum is 4,500 Btu/h for a cleaned tube or 4,100 Btu/h where the tube cannot be cleaned without shutting down the burner.

No. Its scope includes powerplant and APU components and installations, including firewalls, nacelle hardware, fluid systems, controls, electrical equipment, fire detectors and related assemblies.

Potentially. Acceptance by similarity, analogy or previous evidence depends on the applicable requirements, configuration similarity and certification-authority acceptance.

No. The certification authority must accept the project-specific compliance strategy, test conditions, deviations and evidence.

• Fireproof vs Fire Resistant Components.

• FAA AC 20-135 Explained.

• ISO 2685 Fire Testing.

• Aircraft Engine Fire-Protection Certification.

• Aircraft Firewalls and Designated Fire Zones.

• Burner Calibration Best Practice.

• Heat-Transfer-Rate Validation.

• Fluid-Handling Component Fire Testing.

• Fire-Detection System Qualification.

• Firewall Sealant Flame-Penetration Testing.

• Fire-Test Boundary-Condition Assessment.

• Aircraft Engine Fire Protection.

• Fire Detection and Extinguishing Systems.

• Propulsion-System Safety Assessment.

• Nacelle Fire Protection.

• Engine Component Qualification Testing.

• Fire-Test Evidence for Certification.

Need guidance on AS6826 certification testing?

Helios provides independent support for powerplant fire-test strategy, AS6826 interpretation, boundary-condition development, test planning, procedure preparation, evidence review and certification engagement.

Develop the compliance strategy before committing hardware and test time. Early technical review can expose weak assumptions, unrepresentative conditions and incomplete acceptance criteria before they become expensive programme problems.

Your Test Facilitator. Not simply a test facility.

• AS6826, issued April 2025.

• FAA AC 20-135 Change 1.

• ISO 2685:1992.

• FAA Power Plant Engineering Report No. 3A, 1961 version.

• FAA Powerplant Engineering Report No. 3A, revised March 1978.

• SAE AIR1377.

• SAE AS8028.

• SAE AS5127/2C.