Resonate provides ISO 2685 aircraft wire harness fire testing, enabling manufacturers to verify fire resistance and continued electrical functionality in designated aircraft fire zones
Aircraft electrical systems are expected to continue operating in some of the harshest environments imaginable. In areas close to engines, auxiliary power units (APUs), and fire zones, wire harnesses may be exposed to extreme temperatures and direct flame impingement. Demonstrating their ability to survive these conditions is critical to both aircraft safety and certification.
Resonate Testing provides ISO 2685 aircraft wire harness fire testing, helping aerospace manufacturers, system integrators, and certification teams verify the fire resistance and continued functionality of electrical wiring systems intended for operation within designated fire zones.
ISO 2685 was developed to evaluate the ability of aerospace components to withstand exposure to a standardised fire environment representative of an engine fire. For wire harnesses, the objective is not simply to determine whether the insulation burns. The test assesses whether the harness can continue to perform its intended function while subjected to a severe flame exposure.
For manufacturers, this testing provides evidence that critical electrical systems can maintain integrity for the period required to support safe engine shutdown and continued aircraft operation in accordance with the applicable certification requirements.
Custom Aircraft Wire and Harness Crosstalk Under Fire Testing is not a standard test name within ISO 2685. Rather, it is a bespoke electrical performance assessment carried out during or after an ISO 2685 fire exposure to determine whether heat damage has caused unwanted signal coupling between wires.
In aircraft systems, crosstalk occurs when a signal on one conductor induces an unwanted signal into another conductor. Under normal conditions this is controlled through:
Insulation integrity.
During a fire test, these protections can degrade. A fire in a powerplant core or fan / accessory compartment may be remote from the Electronic Engine controller (EEC) / Full Authority Digital Engine Controller (FADEC) however it may cause spurious signals input into the engine controller from failing harness in the fire area.
As harness temperatures rise:
Carbonisation of insulation can create leakage paths.
A harness may continue to show electrical continuity while still suffering degraded signal integrity.
For many modern aerospace systems, particularly those carrying:
A continuity-only assessment is often insufficient.
Resonate Testing’s fire laboratory is equipped to perform demanding aerospace fire test programmes, including:
Post-test inspection and failure analysis.
Throughout testing, we can monitor electrical continuity, insulation performance, functionality and other customer-specific parameters to determine how the harness performs during and after flame exposure.
A custom test may involve:
Aerospace test standard used to evaluate the fire resistance of aircraft components installed within designated fire zone.
An area of an aircraft where a fire could reasonably occur and where components must demonstrate fire resistance capability.
An assembly of wires, cables, connectors, clamps, sleeving and protective devices routed together as a single unit.
The ability of a component to continue performing its intended function while exposed to a specified fire condition.
Verification that the test burner produces the specified flame temperature, profile and heat flux required by the standard.
The rate of thermal energy transferred to the specimen, typically expressed in kW/m².
The condition in which the physical structure of the harness remains intact during and after testing.
Verification that electrical conductors remain electrically connected throughout the test.
Ability of a circuit to continue carrying power or signals during fire exposure.
Ability of a harness to transmit signals without unacceptable distortion, attenuation, errors or interference.
Electrical resistance between conductors or between conductors and ground, used to assess insulation performance.
Ability of insulation to withstand an applied voltage without electrical breakdown.
Unwanted electrical coupling of signals from one conductor into another conductor within a harness.
Assessment of whether thermal damage degrades shielding or insulation sufficiently to create unacceptable signal interference.
Most of the currently used wiring was tested using propane burners. These were qualified before FAA AC 20-135 Change 1 (Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria), issued 11 October 2018. This change explicitly removed guidance that had previously allowed the SAE 401 propane burner and stated that propane does not represent combustible fluids likely to exist in an aircraft engine fire. The FAA concluded that kerosene burners produce a more severe and representative fire environment. From the EASA side, the corresponding shift occurred through EASA’s acceptance and harmonisation with SAE AS6826.
The fire environment generated by a kerosene burner is extremely severe and wire systems must not only survive direct flame exposure, but also maintain the required electrical performance and system functionality.
Resonate has performed testing of wires of various standards and confirm that it remains extremely challenging to produce conductors that will pass ISO2685 testing with a Kerosine burner. As a result, many engine and airframe and system manufacturers continue to specify proven wire technologies with extensive service history rather than qualifying entirely new wiring systems from new suppliers. For this reason, demonstrating successful ISO 2685 compliance remains a significant milestone for any new aerospace fire zone wire or harness design.
Resonate testing provides high quality fire, mechanical, and environmental test solutions and certification services across a wide range of industrial sectors. From Primes to SME’s, Resonate Testing provides a bespoke and tailored service to our clients.
Whether you’re looking to contact us for the first time or have another testing requirement, we’d love to hear from you.
