Airplane condition lever

Answer 1

Condition levers are used on turbo-prop aircraft, that is, an aircraft in which a gas turbine powers a propeller which provides thrust to make the aircraft move. The condition levers govern the amount of fuel that enters the gas turbine - as levers are advanced, more fuel is added and the engines provide more power. Most aircraft condition levers have two settings, "high," which is used for takeoff and flight, and "low," which is used for taxi or situations in which less power is needed. Some also have "cutoff" settings, which intentionally starve the engines of fuel to the point of shutdown.

More specifically, these levers set the power of aircraft idle - that is, when 0% power is applied while engines are running. Thus these levers are also known as "idle condition levers." "High" idle is necessary for takeoff or situations that require access to more immediate power (such as landing approach when the pilot may need to abort the landing, immediately apply full thrust, and climb back to a safe altitude quickly), however a higher idle is inefficient for taxi when only a small amount of power is needed to overcome the aircraft's inertia and move it down the taxiway.

"Condition" setting is similar in concept to "mixture" setting in a piston engine, however they should not be confused as they are quite dissimilar in practice. "Mixture" governs the ratio of air to fuel as it's aspirated into a combustion chamber. It therefore enables the engines to operate more efficiently in flight by reducing the fuel in the aspirated mixture commensurate with the lower oxygen level in the atmosphere at higher altitudes. Since turbo-prop aircraft inject fuel into compressed, high-velocity air already in a continuous combustion state, they have no carburetors (and no aspiration), and therefore no "mixture" per se can be set. It is also worth noting that unlike "mixture" in piston engines, "condition" is not an infinitely scalable setting. High," (flight) "low," (taxi) and "cutoff" (shutdown) are the only three positions that can be utilized on most turbo-prop condition levers, whereas "mixture" levers can be moved to govern any level of mixture between full and cutoff.