It’s been a decade since wiring problems led to the crashes of TWA Flight 800 and Swissair Flight 111. Years of regulatory work to address shortcomings in aircraft electrical wiring systems has finally resulted in a FAA rule to address the problem.
FAA’s Enhanced Airworthiness Program for Airplane Systems/Fuel Tank Safety (EAPAS/FTS) "requires holders of type certificates for certain transport category airplanes to conduct analyses of their airplanes and make necessary changes to existing Instructions for Continued Airworthiness to improve maintenance procedures for wire systems." The final rule was published in 2007, and it becomes law in 2011.
The EAPAS requires airlines and repair shops, in particular, to develop new procedures that treat wires as integrated systems instead of standalone bundles.
"The big issue in industry today is the new wiring regulations related to electrical arcing and chafing that leads to the breakdown of insulation," said Ray Frelk, vice president of sales and marketing for ECS/Carlisle Interconnect Technologies, of Franklin, Wis. "The regulations are designed to reduce the risks of wire chafing."
ECS was acquired by the Carlisle Companies, of Charlotte, N.C., in October, joining the Carlisle Interconnect Technologies division.
Some industry experts estimate there are two in-flight smoke incidences somewhere in the world each day and one of those is precipitated by faulty wiring. Also, there is concern that the number of smoke incidences could rise as high-power in-flight entertainment (IFE) systems become more prevalent in aircraft.
"With IFE to every seat, there is a tremendous amount of power consumed and heat generated," Frelk said. "There is a fair amount of abuse that the wiring is exposed to that wasn’t envisioned years ago."
The FAA EAPAS/FTS addresses many of those issues by setting specific separation standards for wiring, even requiring modification and maintenance shops to go back and rewrite old supplemental type certificates (STC).
"In the past, standard wiring practices allowed some flexibility to use standard practices to install wiring onboard aircraft," Frelk said. "Now the FAA is becoming much more strict to ensure that the wiring installed on the airplane is done with the same level of integrity for every installation."
While developing plans to deal with the new FAA rule, companies are simultaneously tackling another major trend in commercial aviation, namely, the proliferation of passenger-owned electronic devices like PDAs, MP3 players and smartphones — all hungry for high throughput through smaller gauge wires.
Frelk said ECS/Carlisle Interconnect Technologies developed a STC for a European carrier to qualify a GSM telephone system on the carrier’s fleet of 737-800s. Frelk said ensuring that the dozens of personal communication devices passengers brought onboard didn’t interfere with aircraft avionics was part of the certification process.
Such regulated compliance differs substantially from the current situation where compliance consists of flight attendants telling passengers to turn off their devices. Human nature being what it is, though, it is likely that a certain number of communication devices remain turned on, potentially sending signals into aircraft wires that could lead to avionics glitches.
"Wiring does have a potential to provide a path to interference if it’s not done properly," said Frelk.
For the installation with the European carrier, ECS/Carlisle Interconnect Technologies had to ensure the avionics would not be disrupted even if all telephones on the airplane were turned on and trying to make calls simultaneously.
That had to be the case even if there was a system failure of the onboard equipment, and all the onboard telephones were attempting to interrogate the ground cellular towers.
The irony, according to Frelk, is that cell phone use once certified requires strict oversight from regulators, while the current situation allows airlines to depend on pre-flight announcements without any means of verifying passenger compliance.
"There is a big gap in perception today in terms of whether the threat is real," said Frelk. "With this installation, we had to validate that carry-on cell phones and other personal electronic devices would not cause interference on brand new 737-800s. Think about all the old 737s, MD-80s and thousands of older planes that are not built to modern EMI standards."
To provide even more guidance on wiring standards and installation procedures, organizations like standards development organization ASTM International and its Committee F39 are developing standards such as F2639 — Standard Practice for Design, Alteration and Certification of Airplane Electrical Wiring Systems.
Document F2639 is listed in the new revision to FAA Advisory Circular 43-13.2b, and reads that coax and triax cable with low-temperature dielectrics and jackets (-40°C to +85°C) such as polyethylene are not to be used.
Also, bare copper conductors are prohibited.
Committee F39 was formed in 2004 to develop standards for electrical wiring system design, fabrication, modification, inspection and maintenance procedures and processes.
"Basically a lot of cable being used is similar to what you would find with cable TV in the home, with the exception of a low-smoke jacket," said Scott Allan, marketing manager for PIC Wire & Cable, of Sussex, Wis.
"The F2639 standard eliminates the possibility of using product like that."
Most passengers, whether they’re sitting on a United 777 or a Gulfstream G550, have higher expectations about in-flight entertainment and their ability to mimic the connectivity capabilities they have in their homes and offices.
For wire manufacturers, that means a constant struggle to develop products with greater throughput that are also of smaller gauge while still eliminating crosstalk and operating over longer distances within the aircraft.
It wasn’t too long ago that state of the art in cabling was Category 5 twisted pair that operated at 100BaseT (followed by Cat 5e, which is the typical Ethernet cable for connecting a computer to the Internet).
Cat 6 cable for 1000BaseT communications, commonly referred to as gigabit Ethernet, is now the norm for most manufacturers.
"There’s a lot more emphasis in the aviation industry on connectivity, productivity and IFE, resulting in more stringent requirements from customers for better cables," said Kerry Stuckart, product manager for coaxial cable at Emteq, based in New Berlin, Wis.
Emteq, for example, manufactures a half-dozen different Cat 6 cables, including a new "Gigaflex" cable with a flexible out diameter designed for easier installation while still transferring data just as fast. The company’s products typically consist of two twisted copper wire pairs with four conductor cables, or four pairs with eight conductor cables.
Newer cables like Cat 6a and 7 provide even greater performance. Cat 6a can support 10GBaseT (10 gigabits/sec) at a distance up to 330 feet, while Cat 7 does the same with less crosstalk and noise.
Installations of such cables, as well as those designed for high-definition television, remain strong, even though aircraft sales are down.
"There’s been a drop-off in forward-fit aircraft programs like at Cessna and Hawker," Stuckart said. "But we’ve seen an increase in the aftermarket because people are holding onto their aircraft longer or buying older aircraft, and then upgrading them."
Design and manufacturing of high-speed cables provides a number of new challenges for companies compared to Cat 5 cables.
"With higher bandwidth and throughput, the issues of temperature, weight and diameter become a greater challenge, especially while maintaining quality," said Allan, adding that a desire to use more commercial off-the-shelf (COTS) technology in order to save money makes it even harder to maintain aerospace-level quality.
"There is a tremendous desire to leverage COTS technology for cost and innovation. Aircraft applications are critical, however, and we must ensure that those products meet quality and reliability standards when adapting that technology."
The continued development of seamless or smooth wire construction is an example of a small change that goes a long way to preventing wire damage that can result in arcing. In such a configuration, a Teflon/Kapton insulation is applied in a tape-wrap manner.
"Even though it has a seam, it is smooth, so when you’re pulling wire through the aircraft, there isn’t an edge to pull up," said Bob Scott, senior wire and cable product manager for A.E. Petsche, of Arlington, Texas, a supplier of wire and cable interconnect products. "It provides greater insulation integrity."
Scott said he sees the industry also moving toward aluminum conductors and hybrid connectors (made with nickel, aluminum and copper construction with composite conductors).
Such designs are finding their way into power feeder cables that carry the main power for the aircraft.
"The benefit is that you get performance in current-carrying capacity of copper, but the weight savings of aluminum," said Scott. "These power feeder cables are usually very large gauge, heavy, have long runs in the aircraft and carry a lot of amps."
Avionics Magazine’s Product Focus is a monthly feature that examines some of the latest trends in different market segments of the avionics industry. It does not represent a comprehensive survey of all companies and products in these markets.
Following are some recent developments announced by manufacturers and suppliers of wire and cable products to the aerospace industry.
* Tyco Electronics, of Harrisburg, Pa., in September introduced a 200°C wire and cable to its ElectroLoss Filterline family of EMI-filtering wires and cables for defense and aerospace applications.
The higher temperature rating allows smaller conductor gauges to be used to reduce weight in weight-sensitive applications, the company said. Additionally, the wire’s cross-linked, high temperature, "non-melting" insulation system offers resistance to the wide range of fluids in aerospace environments. It meets all mechanical and electrical requirements of M85485/9-12 and exceeds the thermal performance requirements. It also is compatible with standard 39029 contacts and associated connectors.
* SEA Wire and Cable, a wire and cable distribution company based in Madison, Ala., in June completed a 34,000-square-foot expansion to its warehouse and office facilities. The company added 8,600 square feet of office space and 25,500 square feet of warehouse space, which adds 33 percent more storage capacity to the facility. The addition also doubled truck bays for incoming and outgoing freight, and increased wire processing space by 50 percent, according to SEA Wire and Cable President Dana Town.
"SEA Wire and Cable has experienced significant growth over the past 5 years," Town said. "With the addition of our 34,000 square feet of office and warehousing space, SEA will be in a position to stock more product for our customers as well as provide additional office space for our growing sales force."
The facility’s warehousing efficiencies, including SEA’s Very Narrow Aisle (VNA) and picking technology will further increase the company’s productivity, Town said.
* In August, Emteq and Custom Control Concepts (CCC), based in Seattle, partnered to develop cables to integrate specifically with CCC’s Cabin Management and in-flight entertainment systems for business and VIP aircraft. Emteq said it tested and received approval for several cables, including those for High Definition Video, Digital Audio, Ethernet and communications, used for integration with the CCC system.
* A.E. Petsche in June signed an agreement with Airbus to supply a range of electrical components and accessories for a variety of airframes. A.E. Petsche will provide Just-In-Time delivery services to Airbus and its electrical sub-contractors worldwide. In addition, the company will provide electronic links between its systems and those of Airbus.
A.E. Petsche Co. www.aepetsche.com
AeroFlite Enterprises www.aeroflite.com
Air Harness Manufacturing www.airharness.com
AirWorks Inc. www.airworksinc.com
Ametek Aerospace www.ametek.com
Amphenol Corp. www.amphenol.com
Brand Rex www.brand-rex.com
Calmont Wire & Cable, Inc. www.calmont.com
Carlisle Interconnect Technologies www.carlisleit.com
Chippewa Aerospace www.chippewaaerospace.com
Christensen Industries www.ci-aviation.com
Cirris Systems Corp. www.cirris.com
Dallas Avionics Inc. www.dallasavionics.com
Data Bus Products www.databusproducts.com
DeCrane Aerospace www.decraneaerospace.com
DIT-MCO International www.ditmco.com
Eaton Corp. www.eaton.com
Electro Enterprises, Inc. www.electroenterprises.com
Glenair Inc. www.glenair.com
Habia Cable www.habia.se
H.S. Electronics Inc. www.hselectronics.com
InterConnect Wire www.interconnect-wiring.com
kSARIA Corp. www.ksaria.com
Marine Air Supply www.marineairsupply.com
MilesTek Corp. www.milestek.com
Phoenix Logistics www.phxlogistics.com
PIC Wire & Cable www.picwire.com
SEA Wire & Cable www.sea-wire.com
Teledyne Reynolds www.teledynereynolds.com
Thermal Memory Ltd. www.shrinkfit.co.uk
Tri-Star Electronics International www.tri-starelectronics.com
Tyco Electronics www.tycoelectronics.com
Vermillion, Inc. www.vermillioninc.com
W.L. Gore www.gore.com
Woven Electronics Corp. www.wovenelectronics.com
Zippertubing Co. www.zippertubing.com