Definition
An emergency condition declared by the appropriate U.S. military authority that indicates an attack against the continental United States, Alaska, Canada, or U.S. installations is considered probable, is in progress, or has occurred.
Plain English
An official military alert warning that an air attack on North America may be coming, is happening, or has just happened. When declared, special restrictions apply to civilian aircraft.
Context Anchor
A pilot may encounter this term in FAA emergency procedures, airspace security information, or instructions issued during a national defense situation.
Derivation
“Defense” comes from an older word meaning “to ward off” or “protect.” “Emergency” comes from a word meaning “to arise” or “come up.” Together, the term points to a sudden, serious situation involving the protection of airspace from attack.
Why Pilots Care
Declaration can impose immediate transponder requirements, radio monitoring, or route changes that affect flight safety and legality.
Intuition Check
Do not read this as a normal in-flight emergency like an engine problem or medical issue. An Air Defense Emergency is a military-level national defense condition involving a possible or actual hostile air or missile attack.
Example Sentence 1
When an Air Defense Emergency is declared, all civil aircraft must comply immediately with ATC instructions and any military intercept procedures.
Example Sentence 2
During the Air Defense Emergency, the pilot maintained continuous radio contact and complied with vectors away from restricted airspace.