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Aviation terminology, in my understanding of it, makes a useful distinction between something being "selected" or "commanded" and "indicated."

For example, if I flip the lever for landing gear from "up" to "down," I've "selected" landing gear down or "commanded" it to be down. This doesn't, of course, mean that the gear is actually down and locked into position so that it's in a suitable state for landing.

Thus there will often be a light or other indicator connected to sensors that determines through means other than the lever position that the landing gear is in the desired state; when this light goes on (or is the correct colour or whatever) it's said that the gear is "indicated" down, giving me some confirmation that the command has been correctly executed.

This, too, doesn't mean that the landing gear actually is in the commanded state; there could be an error or malfunction in the system such that the landing gear is indicated in that state but is not, or vice versa.

There is surely a third word used to say what the true state is (even if this state may not be easily detectable by the pilots). What is this word?

(If I've got my terminology wrong here, or there are multiple terms used for these things, please correct me in your answer.)

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    $\begingroup$ Perhaps "confirmed"? $\endgroup$
    – quiet flyer
    Jul 21, 2022 at 17:12

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The word is "actual".

"Selection" refers to the interface between the human and the hardware. Finger or hand, and switch, or selector handle. A selection is a human choice.

A "Command" refers to the signal resulting from the selection, within the hardware or software system, that initiates the actions to get the final result . Switch moved to position A, results in signals to a controller that tell the controller to do this or that, to get the result intended by the human. The controller received a command from the switch, when the pilot made the selection.

"Indication" tells the human that the final result was what he/she wanted.

The true state resulting is the "actual" state. Hopefully it matches the indication, or if the indication circuit is lying to you because of a malfunction, it doesn't.

So, if gear is only halfway down even though you have a down and locked indication, you'd say halfway down is its actual position after visually looking at it yourself, and Houston, we have a problem.

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  • $\begingroup$ Depending on design, an "indication" can be based off either the selected or the actual state. "Talkback" is a useful word sometimes used for the latter. Gear indicators are usually talkbacks. (Of course talkbacks can still fail in a way that they no longer reflect the actual state!) $\endgroup$
    – TypeIA
    Jul 21, 2022 at 17:31
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    $\begingroup$ Was in the aerospace business 40+ years and have never heard the word "talkback". That sounds like something from another industry. You just say "downlock indication", "in transit" indication, etc. Or maybe it's a Boeing thing? $\endgroup$
    – John K
    Jul 21, 2022 at 17:40
  • $\begingroup$ It's not specific to gear indicators. From poking around in the Google, it seems this term may be mostly limited to spacecraft. $\endgroup$
    – TypeIA
    Jul 21, 2022 at 19:02
  • $\begingroup$ +1 for actual. Another sub-type of indicated + actual is verified $\endgroup$
    – Jim
    Jul 21, 2022 at 21:53
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    $\begingroup$ "Verified" or "confirmed" refers to something the pilot has done. The actual state is the true state, whether or not the verification/confirmation (whatever that entails for a given system) has been performed. $\endgroup$
    – Ralph J ♦
    Jul 22, 2022 at 4:44

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