What is the Weeping Wing System?
The weeping wing system—also known as a ‘running wet’ or ‘evaporative system’—marks a significant advance in aviation ice protection technology. Rather than waiting for ice to form and then mechanically breaking it apart, this system works proactively by continuously bathing critical aircraft surfaces in specialized de-icing fluid.
This technology operates by channeling specialized de-icing fluids, typically based on ethylene glycol or isopropyl alcohol, across critical surfaces. This creates Uninterrupted protection that proves invaluable during prolonged exposure to icing conditions.
The most widely recognized commercial implementation is the TKS (Thompson Kelly Services) system, which has become the industry gold standard for general aviation aircraft. This system excels at providing comprehensive, simultaneous coverage across multiple surfaces, forming a protective barrier against ice formation.
How the Weeping Wing System Works
The system operates by pumping glycol-based fluid from onboard reservoirs to ice-vulnerable surfaces—wings, stabilizers, and propellers. These critical areas feature leading-edge panels embedded with thousands of microscopic laser-drilled holes or constructed from porous metal mesh, creating an intricate distribution network for the protective fluid.
Once the fluid emerges, airflow carries, carrying the glycol solution rearward to form a thin, protective film across the surfaces. This protective film both prevents ice adhesion (anti-icing) and dissolves existing ice (de-icing): The system works continuously while fluid remains available.
Unlike cyclical mechanical systems that operate in bursts, the weeping wing provides continuous protection. Pilots maintain oversight through quantity indicators and control consumption via multiple flow settings:
Glycol Fluid Properties and Usage
The system relies on its specialized ethylene glycol-based fluids. These solutions are designed with extremely low freezing points—well below −70°F (−57°C)—essential for high-altitude flight.
Beyond their freeze resistance, these fluids are carefully formulated to be non-corrosive and completely safe for aircraft paints, metals, and composite materials. The viscosity is carefully adjusted to provide optimal surface coverage while minimizing consumption—balancing coverage with consumption.
Benefits of the Weeping Wing System
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Comprehensive Surface Coverage: Unlike de-icing boots, the fluid flows back from the leading edge to protect the entire airfoil surface, preventing hazardous run back icing.
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High Reliability: The non-mechanical design has no moving parts, leading to higher reliability, reduced maintenance, and silent operation.
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Proactive Protection: The system can be activated preventatively before entering icing, maintaining a clean airframe and avoiding performance degradation.
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FIJI Certification: It provides a pathway for aircraft to gain FAA approval for Flight Into Known Icing (FIJI) conditions, increasing operational flexibility.
Challenges and Limitations
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Finite Fluid Capacity: Limited onboard fluid capacity constrains protection duration to typically 1–3 hours, requiring careful flight planning.
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Added Weight: The complete system and its fluid payload add significant weight—often 50-100 pounds—reducing the aircraft’s useful load capacity.
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Maintenance and Cost: Those microscopic panel perforations are susceptible to clogging, while the specialized fluid commands premium prices, both factors driving up operational expenses.
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Environmental Impact: Glycol-based fluids require proper handling and disposal due to potential ecological effects.
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Activation Lead Time: The system must be activated before entering icing to be effective, demanding pilot foresight.
FAA Certification and Standards
The FAA has strict certification requirements for all ice protection systems, with weeping wing technology subject to thorough review. Manufacturers seeking approval must show full compliance with FAR Part 23 or 25, proving their systems provide adequate safety margins in severe icing scenarios.
FAA certification for weeping wing systems requires extensive testing to confirm performance and safety standards:
Pilots must follow limitations detailed in the FAA-approved Aircraft Flight Manual (AFM) or Pilot’s Operating Handbook (POH). These documents specify whether the aircraft qualifies for Flight Into Known Icing (FIJI) operations or remains limited to inadvertent encounters—an important difference, as not all TKS installations achieve full FIJI certification.
The FAA also sets maintenance standards through Airworthiness Directives (AD’s) and service bulletins. These regulatory documents mandate specific inspections, fluid replacement schedules, and functional testing protocols required to maintain the aircraft’s airworthiness certificate.
Future of Ice Protection Systems in Aviation
The future of ice protection technology expands on weeping wing technology while tackling current limitations. Progress comes from advances in aircraft design and growing environmental awareness in the aviation industry.
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Hybrid Systems: Combining fluid-based protection with electrothermal elements to reduce fluid consumption and improve effectiveness.
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Sustainable Fluids: Developing biodegradable alternatives to traditional glycol to reduce environmental impact.
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Advanced Distribution: Using smart materials and sensors to automatically adjust fluid flow based on real-time icing conditions.
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Affordable GA Systems: Creating lower-cost TKS installations for inadvertent icing encounters to make the technology more accessible.
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UAV Adaptation: Designing specialized systems for the unique endurance, weight, and autonomous operation requirements of unmanned aerial vehicles.
These developments lead to more integrated, efficient, and environmentally responsible ice protection systems. Weeping wing technology will continue as a cornerstone component of aviation safety.