Operability is the ability to keep a piece of equipment, a system or a whole industrial installation in a safe and reliable functioning condition, according to pre-defined operational requirements.
Design and development responsibilities include the components through which the thrust/power-producing flow passes, i.e. the intake, compressor, combustor, fuel system, turbine and exhaust.
They also include the software in the computers which control the way the engine changes its speed in response to the actions of the pilot in selecting a start, selecting different idle settings and higher power ratings such as take-off, climb and cruise.
The engine has to start to idle and accelerate and decelerate within agreed, or mandated, times while remaining within operating limits (shaft speeds, turbine temperature, combustor casing pressure) over the required aircraft operating envelope.
Operability is considered one of the ilities and is closely related to reliability, supportability and maintainability.