Down to the wire

A University of Dayton Research Institute (UDRI) chemist who identified a plausible cause of the explosion that downed TWA flight 800 in 1996 has developed a self-healing wire designed to prevent that kind of explosion from recurring.

Bob Kauffman also made an accidental secondary discovery that could prove equally lifesaving: damaged aircraft wires exposed to moisture emit radio frequencies just before they short out - a phenomenon that could allow them to be readily located with a simple 'listening' device before they cause any damage.
  
Kauffman and his colleagues at UDRI were part of a team hired by the FAA in 1999 to determine the cause of the centre-wing fuel tank explosion that brought down TWA 800.

The Boeing 747 crashed into the Atlantic Ocean shortly after takeoff from New York City's Kennedy Airport in 1996, killing all 230 passengers and crew. The researchers determined that frayed fuel-sensor wiring likely played a significant role in the explosion.

During his research, Kauffman also showed that frayed wires exposed to moisture in a fuel tank cause conductive fuel residues to form. He said: 'If those residues are exposed to current from faulty wiring, they become red hot and can ignite the surrounding fuel.

'Ageing aircraft wire is a major challenge to the aerospace industry. Over time, bending, chafing and brittleness cause insulation to wear or break away, which can lead to arcing of the bare copper conductor. The results can range from maintenance headaches to a catastrophic event.'

But locating faulty wiring is a daunting task at best, because much of it is not easily accessible. Kauffman's solution is a PATCH - Power-Activated Technology for Coating and Healing - for wire insulation. The non-toxic formula draws on water and electricity to chemically transform it into a permanent coating.

The PATCH system comes in two forms, both based on polyvinyl alcohol. One is a water-based liquid, similar to a contact lens solution, which can be misted into hard-to-reach compartments. The other is a solid, water-soluble material, much like coatings used on vitamins and pain relief tablets, to be used as an inner layer of coating during wire manufacture.

Kauffman added: 'The liquid can be sprayed directly onto wire bundles. If it comes into contact with any live wire with damaged insulation, the electrical current will transform the spray into an insoluble polymer coating. Any solution not coming into contact with exposed wire will wash away, preventing weight build-up.'

The solid PATCH can be built into the wiring between the copper wire and its insulation. Already in contact with electrical current, the chemical coating needs only water to transform into a permanent repair - which takes place when the insulation is breached.
 
Condensation occurs when an aircraft descends from freezing, high-altitude temperatures to warmer low-altitude temperatures. Kauffman explained: 'So if there is a break in the outer insulation, moisture inside the aircraft activates the chemical process that transforms the soluble inner coating into a permanent seal.'

Kauffman is working to commercialise both products. He said: 'The self-healing coating is so inexpensive, it could easily be used in many electrical applications ranging from home repair to industrial power boxes.'

Kauffman has been awarded $200,000 (£102,550) in FAA funding to further develop and test the PATCH technologies, which are patent pending.

Some of the funds will also be used to develop a new technique designed to find faulty wires before they cause harm. Kauffman discovered that damaged aircraft wires exposed to moisture emit radio frequencies just before they short out and believes that technicians could use hand-held listening devices to locate faulty wires.