Malaysian authorities revealed later that military radar had tracked the plane as it turned back to the west and flew across the Malaysian Peninsula, up the Strait of Malacca, before flying out of radar range at 2:14 a.m. and vanishing once again.

CNN: Pilot spots large object off Reunion Island

Each Global Hawk has infra-red and radar sensors, and a surveillance range of 100 miles.

ECONOMIST: Unmanned aircraft

Controlling planes over oceans presents all kinds of challenges because aircraft are out of normal radio and radar range.

WSJ: How New Air-Traffic Control Systems Operate Over Oceans