Product Focus: Switches

Many of the small bits and pieces in the avionics world don’t change much from year to year. That’s true of a lot of technologies. But every decade or so comes a fresh new approach that shakes one of those traditionally staid businesses to its roots.

That’s been the case with avionics connectors, for example. The revolution in high-speed, high-bandwidth data transfer and the extensive use of non-conductive composite materials in aircraft like the Boeing 787 Dreamliner have inspired connector designers working on new products.

Now, a lot of brain cells are being turned on again in the aerospace switch industry, which is about to see the first solid-state switches brought to market. Korry Electronics, an Esterline Technologies Corp., subsidiary based in Seattle, is presently conducting highly accelerated lifecycle tests for what it says is the industry’s first line of solid-state switches. This comes just a decade or so after Korry introduced solid-state LED illumination on the Boeing 777.

Testing will continue into 2009, with flight tests involving an unnamed commercial aircraft manufacturer scheduled to begin in the second quarter, said Bryan Bakker, Korry systems control product manager.

Bakker explained the impetus behind the development of what Korry is calling its "Opticon" line of low-profile cockpit switches. "With mechanical switches you still have reliability problems because of the copper contacts and the actual switching," he said. "As aircraft have become more digital, their switching requirements have gone from high to lower current levels, and mechanical switches aren’t effective at low levels."

Naturally smaller than corresponding mechanical switches, solid-state switches create a number of new design possibilities for cockpit panels, particularly overhead panels where space is at a premium due to the fuselage configuration.

"The depth of a panel is set by the depth of the components," Bakker said. "We started first with push-button switches, but also now make rotary and toggle switches because it wouldn’t make sense to shrink the depth of a push button if you had to put it next to a mechanical rotary switch in a panel."

Korry can provide control panels that are two inches or less in depth, regardless of what switches are in the panel, so long as they are all from the Opticon line. Although there aren’t any new fuselage shapes under consideration today, Korry engineers would be able to take advantage of thinner overhead panels to optimize cockpit shape and fuselage profile for lower air resistance, which would improve fuel efficiency.

Thinner overhead panels could have near-term applications, however, for retrofits and follow-on versions of existing aircraft.

"There’s not a lot of space up there, and OEMs want [overhead panels] to take up less room and not to interfere with the structure or wiring," Bakker said. "We decided not to make an incremental jump but to make a bigger jump."

Korry engineers estimate the Opticon technology offers a weight savings of about 50 percent over conventional cockpit control systems now in use. Besides a direct weight reduction in the cockpit, Opticon technology’s digital interface minimizes the need for wiring and its associated weight throughout the aircraft.

There were a number of engineering challenges associated with the development of these switches, which are a new design, not a redesign.

"We had to make sure that with the method we’re using that components in proximity with each other don’t offset the performance of each other," Bakker said. "A certain field could be generated with switch one that could affect switch two."

The feel-to-touch and other human factors associated with the solid-state switches were dictated by what’s gone before. In other words, the operation of the Opticon switches had to offer no surprises to the cockpit crew.

"We looked at the ways people could design different control panels, and what the customer still wanted was human factors such as full travel for push buttons," said Bakker. "So we maintained all the human factors that pilots want in the feel and action of the switches.

"The FAA also had a lot of influence. For a particular function they want it to behave in a certain way."

In a smoke-filled cockpit, for example, FAA wants push buttons to travel the same distance that they always have so there won’t be any question in the minds of the pilots that a particular switch was activated or not, regardless of whether they could visually see the switch.

There’s always a lot of talk in the industry about bringing technology like touch screens to the cockpit, but because of those human factor considerations it is unlikely touch screens will be used any time within the next decade for safety critical activations. The same is probably true for keyboard-type switches with limited travel (such as that found on a computer keyboard), as well as voice-activated switching systems.

Old As New

For the reasons just stated, the phrase "what is old is new again" is apropos for aviation, particularly for technologies like switches.

"The yardstick in this business is making new products indistinguishable from old ones," said Loren Jensen, president and COO of Aerospace Optics, of Fort Worth, Texas, which is known for its Vivisun line of lighting products. Jensen added that the long lead times common in avionic systems development necessitate new products that at least mimic the look and feel of older products, if not much of their functionality.

"Pilots and OEMs and the military are very conscious of human factors. We could make switches as small as the switches on a Blackberry, but is that what you want a pilot in turbulence or a helicopter pilot to use? Making switches smaller doesn’t necessarily bring any more benefits to the cockpit."

In that respect, Jensen is seeing a movement away from current-carrying switches to logic-level switches that are not in the electric flow. Such a low-current switch is akin to a garage door switch on the wall in that it is not tied to the electric current but instead sends a signal to the motor to start spinning and open or close the door.

"The technology is being driven by industry always looking at space and weight and ease of installation, and logic-level switches can bring those types of benefits to bear," Jensen said.

In addition, switch design and construction have to address many of the same issues affecting other avionics components, particularly isolation from electrical events.

"One of the driving forces is the increased environmental considerations that this equipment needs to endure, like lightning strikes and severe electrical environments," said Jensen. "As OEMs go to more composite aircraft, the question of how the airplane handles the electrical environment becomes key.

"The question becomes, how do you continue to make these components less susceptible to the environment? It requires companies like ours to focus and bring resources to bear on product research and development, and to continually press the envelope on the components that are integral to the switch."

Jensen said the switch industry is experiencing a convergence of differing environmental standards from both civil and military sectors.

"What do we need these components to do? It’s not just lightning we need to address. In the military especially, there are more robust and active transmitters. The nearer these devices are to the switches the more insulated they need to be from them," he said.

Perhaps the biggest challenge for switch makers is one that every company in aerospace is now having to face — the faltering economy and its still-unknown affect on aircraft production, manufacturing jobs and airline load factors.

"We plan to put resources against product development, and take this as an opportunity to double activity in that area," Jensen said. "We’ve experienced years of higher-than-average growth, and we’ll continue to make little steps along the way and also look at new technologies to ready us for the next leap.

"At the same time, all of us need to be diligent managers of inventory."

Avionics Magazine’s Product Focus is a monthly feature that examines some of the latest developments in different market segments of the avionics industry. It does not represent a comprehensive survey of all companies and products in these markets.