British reporters aboard the Royal Navy ship Ocean said that both helicopters returned safely after missions lasting less than two hours.
The Australian ship Ocean Shield left Perth to head for the search zone on Monday, equipped with a US black box detector and an underwater drone.
The Australian Navy ship Ocean Shield is heading to the region and has equipment for detecting the plane's "black-box" flight recorder.
Experts are still urging caution at this stage, but if these "pings" detected by the Australian ship Ocean Shield are confirmed a recovery operation could at last get under way.
The initial search area - roughly in the region where "pings" were detected by Australia's naval support ship Ocean Shield on 6 April - covers some 40 sq km (15 sq miles).
Marine pollution, destruction of critical habitats, entanglements in fishing gear, collisions with high-speed ships, ocean noise pollution, and global warming remain dangerous hazards.
A pinger locator lent by the U.S. Navy was being towed by the Australian ship Ocean Shield, trying to pick up signals from the Boeing 777's flight data recorder.
In October, Reuters described an incident involving an oil and gas exploration ship, Ocean Rig Poseidon, which was able to thwart an attack with the assistance of on-board security personnel and with the support of the Tanzanian Navy.
These ships were called Ocean ships with each ship's name starting with Ocean.
