[appreciatorBus]

Just an amateur av-nerd, but from what I gather the army helicopter would have had a compatible TCAS, but TCAS won't issue instructions (RA / Resolution Advisory) below 1000 ft. Unclear what happens when one aircraft is above 1000 and one is below, but video seems to imply that the plane got an RA to immediately climb and did so, while presumably the helicopter just got a Traffic advisory without any required instruction to follow.

[kevinsundar]

Ah that's really good to know. Makes sense for it not to operate under 1000 ft since you clearly can't have a "Dive" RA for the lower aircraft. I assume maybe just the higher aircraft gets the "Climb" RA then by design.