The phrase "an active line" is correct and usable in written English.
It can be used in contexts where you are referring to a line that is currently in use or operational, such as in telecommunications or project management.
Example: "The technician confirmed that there is an active line connecting the two offices, allowing for seamless communication."
Alternatives: "a live line" or "an operational line".
Foster said police were following an active line of inquiry.
"Even the Met occasionally uses psychics as an active line of inquiry".
"How he came to be in possession of that gun is an active line of inquiry for us," said DS Wallen after verdict.
The lawsuit, filed last week in a federal court in Newark, alleges that Perth Amboy cannot condemn the track because it is an active part of Conrail's Perth Amboy line, and that only the Surface Transportation Board in Washington can declare an active line abandoned.
Nonlinear optimization is an active line of research, given the wide range of scientific fields that benefit from its development.
"We're still examining exactly what data that was, how secure it was and how anonymized," he added saying "it's part of an active line of enquiry".
It presents an active lining concept based on an arrangement of electroacoustic absorbers flush mounted in the duct wall.
This has been a very active line of research.
In the context of Opportunistic Networking (OppNet), designing routing and delivery protocols is currently an open and active line of research.
In this study, we report a new Mu element, Mu13, which was identified from the UniformMu population, a derivative Mu active line from the Robertson's Mu line.
From an affective science perspective, disentangling mechanisms responsible for attending to emotional stimuli from other processes, such as those associated with the organization of autonomic or hedonic responses, is a relevant and active line of research (Pourtois, Schettino & Vuilleumier, 2012).
