Cardiff City's new signing disappeared with pilot David Ibbotson over the English Channel on 21 January.
The Air Accidents Investigation Branch (AAIB) said its Geo Ocean III vessel arrived on Sunday morning to the search area.
Together with a privately-funded vessel, it is conducting sonar surveys off Guernsey.
The AAIB said its search was expected to last three days, while the private search will continue "until the plane is located".
Cushions believed to be from the plane were found on a beach near Surtainville, on France's Cotentin Peninsula, on Monday.
Argentine Sala, 28, and Mr Ibbotson, 59, from Crowle, North Lincolnshire, were travelling from Nantes, where Sala previously played, when the flight was lost.
Speaking from Guernsey harbour, Mr Mearns said his team would work jointly with the AAIB's vessel.
They plan to search an area covering four square miles about 24 nautical miles north of Guernsey.
The location has been based on the flight path before it lost radar contact, said Mr Mearns, a shipwreck hunter.
An official search following the plane's disappearance was called off after three days with Guernsey officials saying there was little chance those on board survived.
It prompted a privately-funded search to be set-up, with £324,000 was raised in an online appeal.
Sala's family arrived on Guernsey following his disappearance and were taken to see the area, circling the island of Alderney.
Mr Mearns said both vessels would divide their search area in half, looking for "wreckage" and a "debris field" in a depth of 60-120m (196-390ft).
"We will continue to work until the plane is located," he said.
More about: plane