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Question

Looking at the 787's throttle quadrant, I noticed that the STAB control switch uses a typical red flip-up toggle switch guard safety cover while for the FUEL CONTROL there is a pull leverlock switch. What is the reason behind using one vs the other? is one "better" than the other?

(source)

Answer 1

Not that one is better than the other, but rather that they are different.

Muscle memory leads to being able to actuate one or the other without looking, and not getting the wrong one.

This is standard UI, and goes all the way down to the controls in your car. Different things and actions have different touch points.

Answer 2

Fuel control switches have integrated red lights (crosses) to warn about fuel/engine fire. The light indicates which engine is concerned and should be switched off.

From familiarization manual:

• Lights must be visible and cannot be covered contrary to stab switches.

• We want to see the switch position and prevent it to be reset to RUN by accidentally closing the cover.

• The switches are locked in a "down" position and must be pulled out before being actuated. When pulled out the switch also unlocks the fire handle that can be used to discharge the extinguisher in the engine.

Of course this can be designed differently, but this is the way which was selected. Having to pull the switch allows also to use this procedure to shutdown an engine in flight (e.g. after an engine fire):

• The first pilot puts their finger on the switch corresponding to the engine to shutdown and asks the second pilot to confirm the engine can be shutdown.

• The second pilots validates the correct switch is being used and the engine can be shutdown.

• The first pilot sets the switch to CUTOFF.

The is to reduce the risk of shutting down the wrong engine, after some mistakes in the past.

Answer 3

The run/cutoff switches are meant to stay in either position for extended periods. Cutoff = parked, run = flight

The stabilizer trim switches are meant to be temporary. Open red cover, move toggle down. When the cover is closed the toggle is automatically pushed back to “norm”.

Answer 4

There is an ergonomic principle which says that controls in a complex system should be differentiated by color, shape and placement, to prevent mistakes. Earlier cockpit designs often had controls which guaranteed mistakes, for instance the B-17 had the flap switch next to the gear switch, and they were identical switches without any differentiation at all. This caused tired pilots in sometimes shot-up airplanes to flip the wrong switch and raise the gear when the were on the ground.

This is a picture of the B-17 controls:

You can see a number of ergonomic errors on this. The gear and flaps are the two red boxes in the picture, identical switches and practically next to each other. the other switches for lights, fuel cut-off valves, boost pumps and lights were all together and identical switches. It was easy to accidentally shut off the fuel rather than turn on the boost pump by mistake, and it did happen.

This is the throttle quadrant and gear switch of a PA-28:

You can see the mixture and throttle are different colors, shapes and placements. The gear is close at hand, but also a very different shape and color. The Boeing cockpits don't use toggle switches partly to make them easily identifiable visually and by feel.