Oi Becker Junior -
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I see you mention 2.4% and 1.2%. These are the second and third/final segment of climb for a 2 engine turbojet aircraft, such as B-737 or MD-80...
If you study the "critical segment" (the 2nd segment) of 3 engine turbojet airplanes, such as a B-727 or a MD-11, it is 2.7%...
And the 2nd segment for a 4 engine turbojet plane, like the B-747 is 3.0%...
xxx
The SID/climb gradient you mention is the actual climb that must be observed for you to comply with a departure. Should you have an engine failure, you will not be able to comply with that departure. Your airline probably will publish engine-out (engine failure) departures routings, should you have a problem to climb on a SID.
xxx
Happy contrails