Definition
A term used to describe a facility, equipment, or component that is not available for use because it is broken, being repaired, being maintained, or otherwise not in a condition to perform its intended function. The term applies to navigation aids, runway lighting, airport equipment, aircraft components, and other items that pilots and controllers rely on.
Plain English
Something that should be working isn't working right now, so you can't count on it.
Context Anchor
Seen in airport notices, controller communications, and status reports for airport equipment, lighting, radio facilities, services, or procedures.
Derivation
Serviceable' comes from the Latin 'servire,' meaning 'to serve' or 'be useful.' Adding 'un-' reverses it: not able to serve its purpose. So 'unserviceable' simply means 'not currently able to do its job.'
Why Pilots Care
Using an out-of-service aid can cause navigation errors or create unsafe situations during takeoff, landing, or en route flight.
Intuition Check
Do not read this as merely inconvenient or temporarily busy. In this context, it means the item is not available or not dependable for aviation use right now.
Example Sentence 1
The ATIS reported that the ILS for runway 27 was out of service, so we briefed the RNAV approach instead.
Example Sentence 2
A NOTAM listed the runway lights as unserviceable until maintenance was completed.