Fire-Extinguishing System Indicating Discs on Engine Nacelles

What do the red and yellow disks on the fire-extinguishing system indicating discs indicate?

1) fuel 2) oil 3) hydraulic 4) brake


Fire-extinguishing system indicating discs on engine nacelles display whether a discharge is thermal (red disk missing) or ground (yellow disk missing).

The two fire-extinguishing system indicating discs, located on the inboard side of each engine nacelle, are designed to indicate different types of discharges. The red disk missing indicates a thermal discharge, usually related to a fire extinguishing event where the system has been deployed to quell a fire. On the other hand, the yellow disk missing indicates a ground discharge, which means the fire extinguishing system has been manually discharged on the ground, typically as part of maintenance or testing procedures.

It is important to note that these indicators are not directly related to the operational systems like fuel, oil, hydraulic, or brake systems. Instead, the NFPA 704 Hazard Identification System may also use color coding such as red and yellow to denote fire hazard and reactivity, but these are not the same as the indicator discs on engine nacelles.

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