Definition
An ATC instruction that allows the pilot to comply with a clearance or instruction at the pilot's earliest convenience, once aircraft handling, workload, or operational conditions permit. The pilot is expected to comply as soon as practical and to advise ATC if compliance becomes impossible. Once compliance is achieved, the pilot reports it to ATC.
Plain English
Do this as soon as you reasonably can. You don't have to do it right this second, but do it at the next sensible opportunity, and tell ATC once it's done.
Context Anchor
Heard in radio instructions from air traffic control when the controller wants an action completed soon but does not need it immediately.
Why Pilots Care
Prevents pilots from attempting an immediate change that could compromise safety or traffic separation.
Intuition Check
Do not treat “when able” as optional or as “whenever you feel like it.” It means the action is expected, but you may wait until you can do it safely and practically.
Example Sentence 1
"Cessna 5732B, when able, climb and maintain seven thousand."
Example Sentence 2
The controller said to turn right heading one eight zero when able, and we executed the turn once we had passed the traffic.