ENG FIRE on ground is performed after a rejected take off in the worst case scenario, or after landing ? . Anyway we are talking about an aircraft stopped , parking brake set and affected engine in fire already at idle. This is when the ECAM ENG FIRE on ground is performed , with an aircraft stopped. If you think about it , a long time has elapsed since you rejected take off , from the moment thrust levers are set to idle and the moment you initiated ECAM actions . That might even be more than the "in flight countdown".
In flight it's different, you would have to wait for a spool down of the engine , as you will go from high thrust to idle ,hence the timing indicated on ECAM in order to increase the efficiency of the Agent , and avoir just discharging an Agent that would be thrown out.
For info , FCOM states for the inflight ENG FIRE : " The 10 sec delay allows N1 to decrease , reducing nacelle ventilation and thereby increasing the effect of the agent". From the moment you call "Stop" decelerate , set park brake , call for ECAM actions , more than 10 seconds have elapsed and engine N1 should be near 20 % .
Last edited by Citation2; 29th September 2019 at 19:27.