Definition
An air traffic control service in which radar-equipped facilities provide pilots flying under visual flight rules with information on observed traffic, advised headings to avoid that traffic, and limited safety alerts. The service is workload-permitting and does not relieve the pilot of the responsibility to see and avoid other aircraft.
Plain English
A service where a controller watching radar tells you about other aircraft near you and may suggest a heading to stay clear, while you are flying by visual rules. You still have to look outside and avoid traffic yourself.
Context Anchor
You may encounter this after canceling an instrument flight plan and continuing visually, when you want to stay in contact with air traffic control for traffic help.
Derivation
Advisory comes from advise, meaning to give helpful information or counsel. That matters here because the controller is advising you, not taking over full responsibility for your flight.
Why Pilots Care
It improves situational awareness and reduces the chance of mid-air conflicts in areas where traffic may not be visible.
Analogy
It is like having someone nearby point out traffic you might not have noticed, while you are still the one driving and staying clear.
Intuition Check
Do not assume “advisory service” means air traffic control is now fully controlling or protecting your VFR flight. It means controllers provide helpful radar-based information when they can, while you remain responsible for seeing and avoiding traffic.
Example Sentence 1
After cancelling IFR ten miles from the field, the pilot requested VFR radar advisory service to help spot traffic in the busy pattern area.
Example Sentence 2
VFR radar advisory service helped the pilot spot a fast-moving jet approaching from behind before it became visible.