Definition
A type of fire extinguishing system, used primarily in aircraft engine and APU compartments, that releases its entire charge of extinguishing agent in a very short time — typically a fraction of a second — through high-pressure discharge nozzles to rapidly flood the protected area and suppress fire.
Plain English
A built-in fire extinguisher that dumps its whole load of fire-fighting chemical almost instantly into an engine bay or similar enclosed space to put out a fire fast.
Context Anchor
Seen in aircraft battery inspection, servicing, and capacity-check procedures.
Derivation
The name describes the action: 'high-rate' meaning a very fast flow, and 'discharge' meaning the release of the agent. The point is that the bottle empties almost immediately rather than metering the agent out slowly.
Why Pilots Care
A battery that fails high-rate discharge testing may not reliably start the engine or supply emergency power.
Analogy
It is like testing a water tank by opening a large valve, not just a small tap, to see whether it can supply a strong flow when demand is high.
Intuition Check
High-rate-discharge does not mean an accidental rapid loss of battery power. In this maintenance context, it means a planned and measured discharge test.
Example Sentence 1
When the crew pulled the engine fire handle and pressed the bottle discharge switch, the HRD system emptied the agent into the engine nacelle almost instantly.
Example Sentence 2
Batteries rated for high-rate discharge are essential in aircraft electrical systems for short bursts of high power demand.