Definition
A category of emergency locator transmitter (ELT) that is mounted to the aircraft's exterior and automatically ejects from the airframe upon impact or, in the case of water, when activated by a hydrostatic sensor. Once deployed, the unit operates independently of the aircraft and transmits a distress signal on the designated emergency frequencies for search and rescue.
Plain English
An emergency beacon that pops free of the aircraft during a crash or water landing and starts sending a distress signal on its own.
Context Anchor
Seen in discussions of emergency locator transmitter types and aircraft emergency equipment requirements.
Derivation
Deployable' comes from the French déployer, meaning 'to unfold or release.' Here it signals that the unit is designed to physically separate from the aircraft, rather than stay bolted in place like the more common fixed ELT.
Why Pilots Care
These transmitters increase the chance of successful rescue when the aircraft itself is damaged, submerged, or inaccessible after an accident.
Analogy
It is like a safety marker that is attached until the accident, then separates and starts calling for help by itself.
Intuition Check
Do not read automatic as meaning the pilot never needs to know about it. Automatic means it is designed to activate by itself after a crash, but the pilot still needs to know what equipment is installed and whether it is serviceable. Do not read deployable as simply hand-carried. Here it means the unit is designed to separate from the aircraft after impact.
Example Sentence 1
The aircraft was equipped with a deployable automatic type transmitter mounted on the upper fuselage, designed to eject and float clear in a water landing.
Example Sentence 2
During the preflight briefing the instructor explained how deployable automatic type transmitters release automatically on impact.