The role of switches is changing in the era of glass cockpits. Today's military and commercial flight decks feature fewer hard-wired, single-function switches and more "soft" switching via pull-down menus and "point-and-click" sequences.
The increasing use of software in aviation is changing almost every aspect of the cockpit, including switches. Many military, commercial and bizjet pilots now use "soft" switches--essentially choices on a computer screen--to manipulate numerous aircraft functions previously handled through single-function switches. While both switch types use a wire or cable to connect into an aircraft system or display, a "hard-wired" switch links directly to a function--and controls that function--vs. linking to a software application that controls the function. Besides consolidating space, soft interfaces allow pilots to scroll through and interact with multiple screens by using the same set of buttons and/or a cursor control device.
Avionics Magazine spoke with human factors engineers who work with military fixed- and rotary-wing aircraft about issues associated with switch use. Near the top of the list is the continuing implementation of soft switches. While computer displays are bringing more software-based functions to the pilot's fingertips, the technology has raised other issues, including pilot workload, safety and situational awareness, menu design, human factors engineering and switch placement.
Early cockpits had a multitude of switches, involving much more manual operation and physical workload. The advent of computers in the cockpit, including multifunction displays with software-driven menus, "has changed a lot of what used to be switches into choices in a computer," says Lisa Billman, a senior manager with ARINC Engineering Services (AES). This has created new issues, she explains, as designers must deal with graphical user interface (GUI) design and menu trees. A menu tree is the hierarchical layout of an entire set of menu options, or pages, for a specific aircraft function or group of functions.
While software-based functions essentially have reduced or eliminated the role of the flight engineer on many aircraft, experts say that computers haven't necessarily reduced pilot workload. Computers may have simplified the appearance of the flight deck, but they have launched an avalanche of data for the flight crew concerning flight status, weather conditions, traffic patterns and aircraft systems.
There are few cockpit switches that are still truly hard-wired, according to the experts. Most cockpit switches now involve some level of interaction with software programs. Some highly critical and emergency functions, such as a kill switch--an override button that shuts off the engine--are likely to always have a dedicated, hard-wired control interface to serve as a backup independent of the flight computers. And light switches and circuit breakers may still be controlled by hard-wired interfaces, and not linked to a software program.
But many other tasks already are linked to input devices that are controlled by software. For example, Billman says, radio on/off switches and navigation aides, most of which were previously manipulated through radio control heads, also are controllable through the soft interfaces of a multifunction display (MFD) or control display unit (CDU).
"There's nothing like going to a straight control panel that has one knob controlling one thing, and you know where it is, and it clearly indicates what state it's in," says Daniel Eksuzian, a manager for human systems engineering with AES. But, he continues, with limited space in the cockpit, designers quickly run out of room, and ever-smaller, cheaper and higher-capacity computers are making their way into several areas of the cockpit.
This creates new challenges, because only so much information can be presented on a single screen--requiring multiple screens and menus, or page trees, to be established. Menu trees represent the logical organization of the pages that a pilot scrolls through on a menu, such as the various weather, positioning, and terrain maps of an MFD. Many MFDs provide a cursor control device, such as a track ball or mouse, or a series of push-button switches on a keypad, to control functions and move back and forth between screens.
The number of software-based choices pilots have, in both the breadth and depth of menus, is significant, however, and the units essentially have become complete workstations.
"You can't just go to a dedicated panel like a flight engineer used to be able to do; you now go through the control display unit," Eksuzian says. He notes that the menu structure can be a major source of workload in the cockpit, and the design is a constant source of discussion in industry circles. Engineering and software designers, he says, generally favor grouping controls and information by system, e.g. hydraulics, engine controls or navigation aids. But pilots typically want displays oriented to specific tasks, such as landing, raising/lowering flaps or targeting.
A pilot today may use the same physical switch to perform several different tasks: the same button on an alphanumeric keypad could be used to enter numbers, letters or symbols. By contrast, in a more traditional cockpit, a single hard-wired switch may control a single aircraft function. In the earlier cockpit, pilots can press a switch and virtually forget about it. But in the computer-driven environment, "You actually have to make sure you're on the right screen and you have to read what it says," Billman explains. If the displays aren't designed correctly, then more "information processing" is required of today's pilots.
What happens if a pilot gets lost on the wrong screen or goes down an incorrect path on the display? Typically there is a "back" key that will return the pilot to the previous page. If that doesn't work, a "home" key will take the pilot to an index-type view of the page tree, which can then be used to navigate back to the desired screen. In a truly high-stress/high-risk situation, the engineers say, a pilot probably would forget about using the computer until the crisis has passed. If the situation involves information buried in a page tree on the computer, the crisis quickly could spiral out of control.
Engineers try to design switches to match pilots' mental model of the unit they are controlling. If a toggle switch is being used in an on-and-off function, like a light switch, it generally should be located such that "on" is indicated by moving the switch up or forward, because of the strong mental association with the light switch. "If a toggle switch was oriented in a way that was incompatible with the pilot's mental association, then errors would be more likely," Billman says.
Many elements are considered in deciding to place a switch in a particular area of the cockpit. Typically, if a switch controls a display, it should be located near that display. Switches also are generally grouped by function; all of the levers and switches associated with landing are typically grouped together. Varying the type or shape of a switch also can help to distinguish its function. If a series of switches is located closely together, engineers can vary the shape or the means of activation (toggle, pull and turn, key-operated, etc.). Designers must be aware of space constraints in the cockpit and consider whether the pilot is wearing gloves and how thick the gloves are. Labeling is also an issue. With limited cockpit space, having enough area to place meaningful labels can be challenging. Nighttime operations also require lighting for switch labels, or the switches themselves.
According to Eksuzian, switch placement boils down to a frequency/urgency issue. Using a broom closet as an analogy, he explains that the broom, dustpan and trash container (or controls pertaining to aircraft attitude, power, radio, navigation information, etc. in the cockpit) are likely to be near the front of the closet, as they are most often used. But the ironing board, winter jacket and other seldom-used objects may be pushed to the back of the closet, where they are easily found but a little harder to reach. Similarly, less frequently used controls, such as light switches and heating/cooling interfaces, may be placed outside the pilot's primary field of view.
A third category would include items that are not used often but that are needed in critical situations. These items are out of the way, but quickly reached in an emergency, such as furnace shutdown switch, a home "911" device or a fire extinguisher in the broom closet. In the cockpit, such items would be outside the pilot's primary field of view, but easily within reach, such as emergency and hi-jack transponder controls and switches for the engine fire extinguisher.
One interesting example of switch placement and safety, Billman says, is the cockpit of the space shuttle, which originally was designed for pilots wearing regular flight suits. After the Challenger space shuttle disaster in January 1986, NASA began requiring pilots to wear full astronaut suits, complete with a large bubble helmet. In the space shuttle, there is a wall of switches located behind the pilots, requiring them to turn completely around--an impossible task with a bubble helmet on. In order to solve that problem, Billman says, NASA installed a rear-view mirror so the pilots could see the switches behind them. For critical switches, pilots have used duct tape-mounted labels written backward to make sure they will hit the right switch in the right direction.
Although many cockpit functions are becoming computer-driven, engineers see the use of switches continuing for at least the next 50 years. But switches may not exist in their current form forever, or, for that matter, have a permanent place in the cockpit. "Why do we need a stick/control yoke, rudders and throttles to control the vehicle if they are just input devices?" Eksuzian asks.
Work currently in the early developmental stages is looking at controlling aircraft systems via pilot thought. Billman believes technology eventually will come to a point where "the airplane will read the pilot's mind and there won't be any switches at all. I really think that's where we're headed, ultimately."
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