The older days (pre 406.25 MHz) the position of downed aircraft was with the the Doppler shift of 243MHz signal,,, if my memory serves me right... It was done by INMARSAT satellites in conjunction with Local user terminals... if a stationary crashed aircraft position can be located than why not a slow flying one?
This approach is not relevant to the current event.
Until a few years ago, 121.5/243.0 MHz ELT signals were located using doppler from the COSPAS/SARSAT satellites. On one pass, the doppler (generated from the satellite's motion) would yield two areas (one on each side of the satellite track). A second pass would determine which of the areas was the actual one in which the beacon should be found.
Doppler Processing