Biological Resistance

Fungus Resistance Testing according to RTCA/DO-160G Section 13
Biological Resistance of Avionics Electronics

The Challenge

Aircraft electronics must operate reliably under a wide range of environmental conditions. While temperature, vibration, and corrosion are often considered primary environmental stresses, biological contamination can also represent a significant risk in certain operational environments.
Aircraft operating in tropical or humid climates may encounter conditions that promote the growth of fungi and microorganisms. Such growth can occur on:

• organic materials used in coatings or insulation
• polymer components and seal materials
• cable insulation or electronic assemblies

Fungal growth may lead to:

• degradation of organic materials
• corrosion due to metabolic byproducts
• insulation breakdown
• contamination of connectors and electronics

To ensure long-term reliability, avionics equipment must demonstrate resistance to microbial growth. Environmental qualification testing according to RTCA/DO-160G includes dedicated procedures for evaluating fungal susceptibility of airborne equipment.
This case study presents the fungus resistance testing of a sealed avionics control module designed for installation in passenger aircraft systems.

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Device Under Test (DUT)

The tested device was a flight control interface module used to regulate auxiliary aircraft systems.
The electronics are housed in a sealed aluminum enclosure designed to protect sensitive internal circuitry from environmental contaminants.
Key characteristics of the DUT
Although avionics bays are generally protected environments, the manufacturer required biological resistance verification to ensure the device remains reliable when aircraft operate in humid or tropical regions.

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Test Objective

The fungus resistance test evaluates the susceptibility of materials used in airborne equipment to microbial growth.
The test verifies that:

• materials do not support fungal growth
• coatings and seal materials remain intact
• •lectronic functionality is not impaired
• no biological contamination affects system reliability

The DUT remained powered during functional verification phases of the test to confirm stable operation.

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Test Setup

Testing was conducted inside a controlled environmental chamber designed for biological exposure testing.
The chamber maintained environmental conditions suitable for fungal growth, including elevated humidity and temperature. Standardized fungal cultures were introduced to simulate contamination that may occur in tropical operational environments.
The DUT was placed in the chamber in a representative installation orientation to ensure realistic exposure conditions.

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Test Conditions

Testing was conducted according to RTCA/DO-160G Section 13 – Fungus Resistance.
Typical environmental parameters include:
The procedure evaluates whether materials used in the equipment provide nutrients for fungal growth or whether protective coatings inhibit microbial contamination.

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Test Procedure

The test program followed the procedure defined in the environmental standard.

1. Pre-Test Inspection
   Before exposure, the DUT underwent:
   • visual inspection
   • functional verification
   • documentation of baseline condition
2. Biological Exposure
   The DUT was placed inside the environmental chamber where controlled fungal cultures were applied to representative surfaces.
   Environmental conditions promoted fungal growth and incubation.
3. Incubation Period
   The equipment remained in the chamber for an extended period to allow potential microbial colonization of susceptible materials.
4. Post-Test Inspection
   After completion of the incubation period, the DUT was removed from the chamber for detailed inspection and functional evaluation.

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Post-Test Inspection

Following environmental exposure, the device underwent detailed visual and functional evaluation.
Inspection activities included:

• surface contamination assessment
• inspection of seals and connectors
• verification of coatings and materials
• electrical functional testing

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Results

The avionics control unit successfully completed the fungus resistance test.
Key observations:
The materials used in the enclosure and electronic assembly did not support fungal growth.

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Conclusion

The tested avionics control module successfully passed the fungus resistance qualification according to RTCA/DO-160G Section 13.
The test confirmed that:

• materials used in the device do not support fungal growth
• coatings and sealing systems remain intact
• the electronics remain fully functional after biological exposure

These results demonstrate the suitability of the device for long-term operation in humid and tropical environments where microbial contamination may occur.

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Why Fungus Testing Matters

Fungus resistance testing plays an important role in ensuring the durability of airborne equipment operating in humid or tropical environments.
Environmental qualification according to DO-160 helps manufacturers:

• identify biological contamination risks early
• validate material selection
• ensure long-term equipment reliability
• support certification of airborne electronics

By verifying biological resistance under controlled laboratory conditions, manufacturers can ensure that avionics systems remain reliable even in the most challenging environmental conditions.

Environmental Qualification according to MIL-STD-810H – Method 508.8 (Fungus)
Fungus Resistance Testing of an Armored Vehicle Radio System

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Background

Military vehicles such as main battle tanks and armored personnel carriers frequently operate in tropical and subtropical climates, where high humidity and temperatures promote biological growth. Under such conditions, fungal organisms can colonize electronic equipment, leading to degradation of materials, insulation failure, corrosion, and functional malfunction.
A particular risk exists for vehicle communication systems, which are often installed inside enclosed hull structures where:

• humidity can accumulate
• ventilation may be limited
• temperature gradients cause condensation

Fungal growth on circuit boards, cable insulation, sealing materials, or coatings can result in:

• electrical leakage currents
• degradation of insulation resistance
• corrosion of connectors
• contamination of optical indicators or displays

Therefore, mission-critical communication equipment must demonstrate resistance to fungal contamination according to MIL-STD-810H Method 508.8 (Fungus).

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Test Objective

The objective of the test was to verify that an armored vehicle radio communication unit is resistant to fungal growth and that its performance is not degraded when exposed to fungal spores in a humid tropical environment.
The evaluation focused on:

• susceptibility of materials to fungal growth
• impact on electrical insulation
• degradation of protective coatings
• operational functionality after exposure

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Device Under Test (DUT)

Equipment:
Vehicle-mounted tactical radio unit for armored vehicles.
Application:
Internal installation in a tank communication rack.
Typical operating conditions:

• Ambient temperature: –32 °C to +55 °C
• Relative humidity: up to 95 %
• Exposure to dust, vibration, and tropical environments

Main Components

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Test Setup

Testing was conducted in a biological environmental chamber designed to maintain controlled temperature and humidity while introducing fungal spores.
Fungal cultures used (typical MIL-STD mixture):

• Aspergillus niger
• Penicillium funiculosum
• Chaetomium globosum
• Aspergillus flavus
• Aureobasidium pullulans

These organisms are selected because they represent common fungi capable of degrading organic materials used in electronics.

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Test Conditions

Testing followed the procedures defined in MIL-STD-810H Method 508.8.
The DUT was placed in the chamber and inoculated with fungal spores. The chamber maintained continuous high humidity to promote fungal growth.

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Post-Test Inspection

After the 28-day exposure period, the radio unit underwent detailed inspection and functional verification.
Inspection methods:

• Visual inspection (magnification)
• Optical microscopy
• Electrical insulation resistance measurement
• Functional operational test
• Coating integrity evaluation

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Test Results

No fungal colonization was detected on the DUT or on any internal electronic components.

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Engineering Assessment

The successful resistance to fungal growth was attributed to several design features:

• Conformal coating of printed circuit boards, preventing nutrient availability and moisture penetration
• Use of non-organic materials for internal insulation components
• Hermetically sealed aluminum housing, limiting environmental exposure
• Military-grade connectors with environmental sealing

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Conclusion

The armored vehicle radio unit successfully met the requirements of MIL-STD-810H Method 508.8 (Fungus).
Even under prolonged exposure to high humidity and fungal spores, the device demonstrated:

• complete resistance to fungal colonization
• stable electrical insulation performance
• full operational functionality

The tested radio system is therefore suitable for deployment in tropical and biologically aggressive environments, ensuring reliable battlefield communication

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Marketing Summary

Reliable communications — even in tropical environments.
Environmental qualification testing according to MIL-STD-810H Method 508.8 (Fungus) confirms that critical military communication systems remain operational even after prolonged exposure to humid and biologically active environments.
Through advanced materials, protective coatings, and sealed system design, manufacturers can ensure that tactical electronics maintain performance in jungles, tropical deployments, and high-humidity climates.