Definition
A passive safety system that works alongside the seat belt and shoulder harness to reduce occupant injury during a sudden impact. In aircraft, it typically takes the form of an inflatable airbag built into the seat belt or shoulder harness that deploys automatically when crash-level forces are sensed.
Plain English
An extra crash-protection system, usually an airbag in the seat belt, that adds to the protection the belt itself provides.
Context Anchor
Seen in aircraft equipment descriptions, maintenance information, and safety briefings for seats or seat belts that include airbags or similar added protection.
Derivation
Supplemental means 'added to' (Latin supplementum, 'something added to make complete'). Restraint means 'something that holds back.' So the term literally means an added system that helps hold the occupant in place during a crash — added to the primary restraint, which is the seat belt.
Why Pilots Care
These systems reduce the chance of injury during turbulence, hard landings, or emergencies by keeping occupants firmly secured.
Intuition Check
Supplemental does not mean the seat belt is unnecessary. It means the system adds protection to the seat belt or shoulder harness; it does not replace them.
Example Sentence 1
Before removing the shoulder harness, the mechanic disarmed the supplemental restraint system to prevent accidental airbag deployment.
Example Sentence 2
During moderate turbulence the supplemental restraint system kept the occupant from shifting forward in the seat.