Every plane in our fleet has an intercom, so that we can talk to one another through our headsets, instead of yelling over the engine noise. The intercoms automatically pick up our voices when we speak into the headset microphone, without us having to press any buttons. The intercom control panel has two knobs on it, one for volume and one for squelch. The volume knob adjusts how loud the voices on the intercom system sound in your headset, and the squelch knob adjusts how strong sounds have to be before they are picked up by the headset microphones and transmitted by the intercom. The intercom is different from the radio, which we use to talk to air traffic controllers, not each other.
At take-off, I typically turn the radio up, so I can hear the air traffic controllers over the engine noise. I might turn it down a little bit in cruise, but I like to keep the radio volume greater than the intercom volume so that cockpit conversation doesn't drown out radio calls. I don't usually adjust the intercom volume at all, unless it's really unacceptable.
Likewise the intercom squelch: unless the intercom is picking up every breath I take and playing it back in my ears, or is so choppy that I only hear half of every word, I usually leave it alone. And seeing as everyone who flies these airplanes keeps the same engines attached to them and wears similar headsets, and they all have to breathe, the intercom controls generally stay in one place.
I wish I could say the same for the intercom control panel. It's a little thing, about the size of the face of a VOR (I guess that's about 10 centimetres across). Two knobs and a switch. Because it's an after-market add-on for the airplane (they didn't come from the factory with intercoms) it has been installed randomly whereever it fits. Different airplanes have different other equipment, so where it fits varies throughout the fleet. And I can never find it. It will be right in front of me, or right under the VOR, or just over by the circuit breakers, or sort of sideways almost by my knee. (If you don't know what a VOR is, substitute "one of those round dially sort of airplane gauge things.") And when I need to make an adjustment it's like it isn't there. I asked maintenance once how to adjust the intercom volume on the airplanes that don't have panel-mounted controls, and they assured me they all do.
You have probably seen these mind games:
Read this first one aloud.
Count the number of times the letter "F" appears, in upper or lower case in the sentence below.
sult of years of scientific
study combined with the
experience of many years.
It's easy to miss the fact that the word "the" appears twice in a row in the first one, and there's a tendency to undercount the F's, missing the ones in the word "of" (there are six F's all together). Somehow for me the intercom controls have become as elusive as F and THE. I know I'm not alone in this, as I once heard a story from a pilot who put six extra hours on an airplane taking it back to a maintenance unit because the radio didn't work. There was a master switch on the panel that he had never seen or used in a summer of flying that airplane. The mechanic had turned off the master during work on the airplane.