In the UK, when receiving a basic service, sometimes the ATC unit passes traffic information. They may say it like this:
“Traffic to your three o'clock, similar level, C172 manoeuvring.”
What exactly is the word “manoeuvring” conveying? Is there a defined point where an aircraft is manoeuvring and when it is not?
To add to @HiddenWindshield's answer, it's explained in UK's CAA Radiotelephony Manual CAP 413:
Traffic Information and Avoiding Action Phraseology
5.21 Relative movement should be described by using one of the following terms as applicable:
(...)
5. 'manoeuvring' where the conflicting traffic’s flight path and/or level information is unpredictable and/or showing significant variation.
I haven't been able to find a precise definition in either the CAA or the FAA's materials. However, as I understand it, traffic that's "maneuvering" is traffic that's not going anywhere in particular.
If someone's flying in order to get somewhere, generally, they're going to be at a specific altitude flying in a specific direction. Course changes will be rare, and generally only occur at specific navigation points, such as VORs or VFR Reporting Points. Such traffic is easy to predict, so ATC can give you a specific heading and altitude for it, and you can assume that that information will be valid for a while at least.
On the other hand, someone that's flying for the sake of flying (e.g. someone doing aerial sightseeing, a student pilot building time, someone checking out a new aircraft, etc.) is going to be a lot harder to predict. They may turn, climb, or descend with little to no warning. That's what I've always understood "maneuvering" to mean: a warning that this traffic is unpredictable, so stay away if at all possible.
Traffic that's maneuvering could be doing any one of several things, ranging from flight training to a post-maintenance check flight, or someone doing aerobatic practice. It's not doing any one thing in particular and may change direction unpredictably and without warning. The alternative to maneuvering is traffic moving in a straight line, perhaps transiting to a practice area, or flying between airports. This type of traffic is much more predictable. Essentially, maneuvering traffic is traffic that can and probably will change direction often. For this reason, if possible, it's likely advisable to avoid that aircraft.
