Definition
An adverb used in NOTAMs and aeronautical publications meaning 'by turns; one after the other in sequence.' Used to describe an action, light, or operation that switches back and forth between two or more states or items.
Plain English
Taking turns. One thing happens, then the other, then back again.
Context Anchor
Seen in NOTAMs and other shortened aviation notices where space is limited.
Derivation
From Latin 'alternatus,' meaning 'one after the other.' The aviation usage keeps this original sense — items or actions taking turns in sequence.
Why Pilots Care
Reading ALTNLY correctly helps a pilot understand whether equipment, lights, routes, or procedures are taking turns rather than being available or active together.
Intuition Check
ALTNLY does not mean “as another choice” here. It means “by turns” or “one after the other.”
Example Sentence 1
The NOTAM stated that the approach lights would flash alternately white and red during the test period.
Example Sentence 2
The beacon operates ALTNLY with red and green flashes during night operations.