Part of the reason is the certification climb criteria:
2-engine transport aircraft, OEI (one engine inop) - min. climb gradient = 3.0%
3-engines, OEI, min. climb gradient = 2.7%
4-engines, OEI, min. climb gradient = 2.4%
I have no doubt that DLH could have climbed out faster, but they religiously use
flex thrust to
set no more than necessary for a safe TO. This lets engines run cooler & last longer.
It's a matter of running their equipment efficiently and economically.
