Product Focus: Connectors

With the introduction of high-speed data communications for the cockpit and the continuing evolution of advanced in-flight entertainment systems in the cabin, avionics connector manufacturers and standards-setting bodies working to define specifications have rarely had more on their plate.

"The aerospace industry has been blessed with a lot of requests for new connector development," said Luc Kaes, multi-signal and fiber optic business development manager with Radiall, based near Paris. "We’ve been quite busy, and over the last 12 to 18 months have seen requests for new architectures, modularity, smaller form factors, and more functions, as well as new requirements linked to higher density."

Kaes described the resultant design challenges. "Electronic components are getting smaller, so the number of inputs and outputs per square inch is increasing," he said. "Our connectors need to be smaller, with a higher density. The challenge is in putting pins closer together without interfering with electrical performance or introducing interference in the signals, and in addressing rising temperatures in the connector. So we need more simulations and to master our processes."

And then there’s the issue of cost, against which everything is judged. Said Kaes: "We’ve been hit hard by the cost of raw materials — gold, silver and copper. Our customers are asking us to find solutions to alleviate those costs. Everybody is now more careful about the types of materials being used.

"The key to avoiding the use of gold or controlling the thickness of gold is in mastering your processes," he said. "Gold and metal are also heavy and weight is a big issue with the cost of oil. So most new connectors are composite connectors. The drawback there is that it is more expensive to invest in the mold. But plastics or composites are gaining ground in replacing parts that used to be metal, particularly in the back shell."

Throw in the conductivity and grounding challenges associated with more-composite aircraft like Boeing’s 787 and Airbus’ A350, as well as environmental standards such as Europe’s REACH (Registration, Evaluation and Authorization of Chemicals) program, which requires manufacturers to identify (and eventually ban) all the toxic chemicals that go into the manufacture of their products, and the industry is spinning in more directions than the electrons passing through the connectors they make.

Standardization Push

Trying to make sense of it all is ARINC and the subcommittees and working groups under its Engineering Standards for Avionics and Cabin Systems committees, which are working to bring standardization to the mish-mash of connectors that are now being employed to address high throughput needs.

For cabin applications, in particular, it is not uncommon to see connectors that were designed for one application being used in multiple other applications for which they were not designed.

"There are a lot of mixed approaches with mixed success with existing products," said Larry Paterson, principal technical designer with Boeing Airplane System Laboratories, who cited EMI problems when common connectors are used for high-speed applications.

"We’re seeing the use of Quadrax, which was developed for Ethernet, being used for digital video and low voltage differential signaling," Paterson said. "We’re seeing a problem in trying to adopt these connectors to other applications."

Paterson also is a member of the AEEC Network Infrastructure and Security (NIS) Subcommittee, which is defining ARINC 664 protocols to implement Ethernet on commercial aircraft. The concern extends beyond the application of the connector to the maintainability of the part, he said.

"As we see a mix of different connectors for different applications, repairs being made to those connectors could be to different standards for different places on the airplane," he said. "Shoehorning existing connectors into new applications has an effect on repairability. We want to limit the number of connector types in order to limit the complexity of connectors being maintained. All of this is active, and these are things we’ve been talking about for several years.

What’s needed, the standards developers agree, is defined systems, protocols, software, hardware and maintenance requirements for the present and coming generation of connectors.

It was just those issues that topped the agenda of the Technical Connector Working Group within the Cabin Systems Subcommittee, which met in Las Vegas in December. It was the third meeting for the working group, which had also met in Hamburg and Dublin over the prior six months.

The gigabit Ethernet connector is at the top of the list for standardization, as the major IFE providers — particularly Thales and Panasonic Avionics — are designing systems that will require gigabit Ethernet (over 1000BaseT) connectors. Connector manufacturers, including Deutsch, Souriau and Tri-Star Electronics International are developing products for gigabit Ethernet.

"We’ve been working in 100BaseT Ethernet up until now, which simply required use of a Quadrax contact," said David Gracey, an aerospace technical consultant who spent 35 years with Boeing and is a member of the Connector Technical Working Group and Cabin Systems Subcommittee. "It’s certainly possible in three to four years that we’ll need a 10 gigabit connector because of the speed at which these systems will be running."

Boeing’s under-development 747-8 Intercontinental, for example, will require gigabit Ethernet connectors, as will the Airbus A350XWB. The 787 Dreamliner uses Quadrax connects, but future versions of the aircraft will likely be enabled for 1000BaseT-and-up connectors.

"Boeing is working along the lines of the industry on a gigabit Ethernet solution as an alternative to Quadrax," said Paterson. "The argument is when do you migrate to fiber? At one point we thought that would be after 100BaseT, but there is still a lot of interest in copper.

"Fiber has several issues associated with it, including requiring airline mechanics to be pseudo telecom technicians. They would have to learn about optical sources. So fiber is good from a weight standpoint, but it has its own set of issues."

Members of connector-related subcommittees and working groups of the Cabin Systems Subcommittee discussed four different categories of connectors needing further definition: (1) those for IFE systems in first and business classes; (2) back-of-the-seat connectors for IFE in coach class; (3) connectors for the IFE passenger control unit; and (4) seat-to-seat connectors.

Manufacturing a connector for the IFE systems used in first- and business-class seats is a challenge because of the articulated arm that holds the video screen. This configuration is also used in the row behind the bulkhead and in emergency rows.

"What’s happening is a problem with the connector between the monitor and the arm because there is not much room in there for a wiring harness and it is difficult to do a gate replacement of that monitor," explained Gracey. "There is a real need to be able to do that, though, because they can’t sell a first-class seat if the monitor isn’t working."

IFE providers in some cases have clauses in their contracts with airlines that make them financially responsible for premium seats that go unsold because of malfunctioning IFE equipment.

"We need a rack-and-panel-type connector that makes it possible to lift the monitor off the arm and replace it with a new one," said Gracey. "You don’t have to mate the connector; just the act of screwing down the monitor means it is always fully mated and sealed against moisture."

The second category would be an improvement over the inexpensive D-sub connector used in the seatback. The connectors have latches that sometimes aren’t properly engaged by the technician, which leads to an intermittent connection when one comes loose. The solution, said Gracey, is a latch with a positive action like a twist so there is a tactile and audible indicator when the connector is fully latched.

The third connector issue is related to the passenger remote control unit that is attached to the armrest with a wire that pulls out of a cradle. Many of the connectors for this type of application have wires soldered to the connector.

"Boeing and Airbus don’t like solder in wiring," said Gracey. "It is impossible to fix at the gate, and, as per the FAA, you can’t use a heating device on an airplane with fuel. You need a crib contact that you can take out with a tool, strip it and put a new contact on without heat."

The fourth need, as defined by connector working groups, is for a seat-to-seat connector, which is expected to be a gigabit Ethernet connector. A daisy chain configuration is used today, but alternatives are desired because of cost and weight. A circular-type connector could be a solution here.

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.