: Why do pilots say, "contact" when starting propeller planes?
Answer : Back before you could simply push a button, turn a key or flip a switch to start an airplane's engine, pilots needed a mechanic to swing the propeller to start the engine. One of the things that needs to be done is to turn off and on a switch that controls the ignition circuit which supplies a spark to each engine cylinder.
A series of verbal commands spoken back and forth were part of the starting sequence, like this:
"Switch off," says the mechanic. "Switch off," confirms the pilot. The mechanic then pulls the propeller through a few revolutions to suck the fuel/air mixture into a few of the engine's cylinders. "Contact!" commands the mechanic. "Contact," repeats the pilot, after he places the ignition switch in the correct position for engine starting. The mechanic then carefully pulls the propeller around, while making sure he stays out of the way. As he pulls the prop quickly and lets it go, the engine, when all the settings are correct, will start.
"Contact" is the word used instead of "Switch on," since that phrase could be confused with "Switch off." Using a completely different word helps eliminate possible confusion in the verbal commands.