Johnson bar (vehicle)
A Johnson bar is a hand lever with several distinct positions and a positive latch to hold the lever in the selected position. The latch is typically activated with a spring-loaded squeeze handle on the lever so that only one hand is needed to release the latch, move the lever, then re-engage the latch in a different position. This is an American English term; in British English, the lever is named for its function.
Many steam locomotives have valve gear controls which are set using a Johnson bar as referenced in Fred Eaglesmith's Back There: Hey Porter, tell that engineer, tell him this train's too slow. Tell him to let go that Johnson bar. I got places I got to go.
Many trucks and buses use a hand brake which is controlled with a Johnson bar. These are sometimes called "Johnson bar brakes".
Truck drivers call the lever control for air-operated trailer brakes "Johnson bars".
On Caterpillar tractors, the forward/reverse lever is also called a Johnson bar.
Some light general aviation aircraft (including Piper Cherokees, Beech Musketeers, and some early model Cessnas) use Johnson bars to actuate flaps and wheel brakes. The Cessna 162 Skycatcher uses a Johnson bar for flap operation. A small number of older aircraft (including the Mooney M-18 and some older M20s) also have landing gear actuated by Johnson bars.
On the Boeing 707/720 aircraft, the Johnson bar was used to manually extend the nose landing gear. This was only used if the normal gear extension failed.