Government helicopter pilot reported a traffic conflict while crossing a runway hold line with another aircraft on short final; at a non-towered airport. The pilot stopped the helicopter short of the runway and the other aircraft landed.

Narrative

MEDEVAC flight taxiing to respond to a local call for a MEDEVAC; noted two aircraft in the pattern as we were walking out the helicopter. The active runway at the time was XX. Conducted startup and proceeded to taxi noting one on the go in the upwind and the PIC glanced at the downwind and base before turning and losing sight out of the left side of the helicopter. As we were taxiing to the runway PIC called for the SIC to clear the left side to which he cleared and immediately followed it with 'STOP STOP STOP' still keying out over CTAF. PIC stopped promptly; still on the taxiway but across the hold short line. SIC noted there was an airplane on short final. Neither the PIC or SIC heard radio calls from the airplane stating the incoming airplane's position; it wasn't until the SIC noticed the landing light that the airplane was identified. Aircraft Y continued their landing rolling past Aircraft X to the next turn off; Aircraft Y did make a call clearing the runway. After the flight PIC and SIC spoke with another Pilot conducting flight instruction who was on the ground running and heard our 'Stop' radio call and noted that he did not hear a base or final call from Aircraft Y even after our taking the runway or 'stop' call when out over CTAF. There was no further incident.