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Too many toggles

Rows and rows of toggle switches

By J. Mac McClellan

Experts can know the age of a horse by counting its teeth. Pilots can identify the age of an airplane design by counting the number of toggle switches on the instrument panel.

Too many toggles
Zoomed image

I think about that every time I’m taking the runway in the recently manufactured Beechcraft King Air 350i that I fly. The King Air by toggle count wins the Methuselah design award.

There are 14 individual toggle switches to flip to ready the King Air from taxi mode to takeoff. And if the weather is cold and crappy, there are three more switches to fumble with. And all but two of the toggle switches are identical in size, shape, and color. They are lined up along the pilot’s subpanel as indistinguishable from one another as white keys on a piano.

Working from left to right the switches control engine auto ignition; engine ice protection; auto feather operation; landing lights; strobe lights; recognition lights; pitot heat; fuel vent heat; and stall warning heat. And if icing is possible for takeoff you need to flip switches for windshield and propeller heat.

Compare that to any recently designed turbine airplane where you find air data system heat controlled by a single switch, even though jets have three pitot tubes compared to the King Air’s two, and in jets the static ports are heated. Landing lights are on one switch, often a two-position switch to select taxi or takeoff/landing mode. Who wants to turn on a single landing light at a time anyway? Only King Air pilots, I guess.

The King Air panel design and multitude of toggle switches dates to the first model built in 1964. And that first King Air 90 was really a turbine conversion of the piston powered Model 88 Queen Air, so the panel design has roots even many more years in the past.

In the bad old days of airplane design human factors considerations didn’t exist, or, if thought of, received the lowest priority. The most direct and uncomplicated way to design a system was to have an individual switch control a single function. And toggle switches can also function as circuit breakers, further streamlining the design and construction of the airplane.

Cessna was among the first to give “switchology” at least some consideration when it developed the Citation. Functions were grouped into a single switch, or at least fewer switches. And Cessna located operational category switches—such as ice protection, or lighting—into logical groups on the panel. They also added color-coded covers on the switches to aid in function identification.

More recent cockpit designs use lighted pushbutton switches the show the position of the switch in plain language, or better yet, remain dark when all is normal. Before LED lighting these switches didn’t work so well because incandescent bulbs got so hot they burned pilots’ fingers.

In the newest cockpits switches of any type are few because touchscreens control nearly all systems and are smart enough to know the phase of flight and what systems need action.

The King has reigned since 1964 and has been built in greater numbers than all other twin turboprops put together, but I’d sure like to fly it with a panel designed in maybe the 1980s or 1990s.

J. Mac McClellan was an editor of Flying magazine from 1976 to 2010. He has 12,000 hours and has flown virtually every GA and business aviation airplane in production during those years. His semi-retirement job is flying a Beechcraft King Air 350i for a company based in Michigan.

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